SMART MODE:

NORMAL GENOMIC

• Lambert de Rouvroit C, Goffinet AM
• Neuronal migration.
• Mech Dev. 2001; 105: 47-56
• Display abstract

• Like other motile cells, neurons migrate in three schematic steps, namely leading edge extension, nuclear translocation or nucleokinesis, and retraction of the trailing process. In addition, neurons are ordered into architectonic patterns at the end of migration. Leading edge extension can proceed at the extremity of the axon, by growth cone formation, or from the dendrites, by formation of dendritic tips. Among both categories of leading edges, variation seems to be related to the rate of extension of the leading process. Leading edge extension is directed by microfilament polymerization following integration of extracellular cues and is regulated by Rho-type small GTPases. In humans, mutations of filamin, an actin-associated protein, result in heterotopic neurons, probably due to defective leading edge extension. The second event in neuron migration is nucleokinesis, a process which is critically dependent on the microtubule network, as shown in many cell types, from slime molds to vertebrates. In humans, mutations in the PAFAH1B1 gene (more commonly called LIS1) or in the doublecortin (DCX) gene result in type 1 lissencephalies that are most probably due to defective nucleokinesis. Both the Lis1 and doublecortin proteins interact with microtubules, and two Lis1-interacting proteins, Nudel and mammalian NudE, are components of the dynein motor complex and of microtubule organizing centers. In mice, mutations of Cdk5 or of its activators p35 and p39 result in a migration phenotype compatible with defective nucleokinesis, although an effect on leading edge formation is also likely. The formation of architectonic patterns at the end of migration requires the integrity of the Reelin signalling pathway. Other known components of the pathway include members of the lipoprotein receptor family, the intracellular adaptor Dab1, and possibly integrin alpha 3 beta 1. Defective Reelin leads to poor lamination and, in humans, to a lissencephaly phenotype different from type 1 lissencephaly. Although the action of Reelin is unknown, it may trigger some recognition-adhesion among target neurons. Finally, pattern formation requires the integrity of the external limiting membrane, defects of which lead to overmigration of neurons in meninges and to human type 2 lissencephaly.

• Matsumoto N et al.
• Mutation analysis of the DCX gene and genotype/phenotype correlation in subcortical band heterotopia.
• Eur J Hum Genet. 2001; 9: 5-12
• Display abstract

• Subcortical band heterotopia (SBH) comprises part of a spectrum of phenotypes associated with classical lissencephaly (LIS). LIS and SBH are caused by alterations in at least two genes: LIS1 (PAFAH1B1) at 17p13.3 and DCX (doublecortin) at Xq22.3-q23. DCX mutations predominantly cause LIS in hemizygous males and SBH in heterozygous females, and we have evaluated several families with LIS male and SBH female siblings. In this study, we performed detailed DCX mutation analysis and genotype-phenotype correlation in a large cohort with typical SBH. We screened 26 sporadic SBH females and 11 LIS/SBH families for DCX mutations by direct sequencing. We found 29 mutations in 22 sporadic patients and 11 pedigrees, including five deletions, four nonsense mutations, 19 missense mutations and one splice donor site mutation. The DCX mutation prevalence was 84.6% (22 of 26) in sporadic SBH patients and 100% (11 of 11) in SBH pedigrees. Maternal germline mosaicism was found in one family. Significant differences in genotype were found in relation to band thickness and familial vs sporadic status.

• Sheen VL et al.
• Mutations in the X-linked filamin 1 gene cause periventricular nodular heterotopia in males as well as in females.
• Hum Mol Genet. 2001; 10: 1775-83
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• Periventricular heterotopia (PH) is a human neuronal migration disorder in which many neurons destined for the cerebral cortex fail to migrate. Previous analysis showed heterozygous mutations in the X-linked gene filamin 1 (FLN1), but examined only the first six (of 48) coding exons of the gene and hence did not assess the incidence and functional consequences of FLN1 mutations. Here we perform single-strand conformation polymorphism (SSCP) analysis of FLN1 throughout its entire coding region in six PH pedigrees, 31 sporadic female PH patients and 24 sporadic male PH patients. We detected FLN1 mutations by SSCP in 83% of PH pedigrees and 19% of sporadic females with PH. Moreover, no PH females (0/7 tested) with atypical radiographic features showed FLN1 mutations, suggesting that other genes may cause atypical PH. Surprisingly, 2/24 males analyzed with PH (9%) also carried FLN1 mutations. Whereas FLN1 mutations in PH pedigrees caused severe predicted loss of FLN1 protein function, both male FLN1 mutations were consistent with partial loss of function of the protein. Moreover, sporadic female FLN1 mutations associated with PH appear to cause either severe or partial loss of function. Neither male could be shown to be mosaic for the FLN1 mutation in peripheral blood lymphocytes, suggesting that some neurons in the intact cortex of PH males may be mutant for FLN1 but migrate adequately. These results demonstrate the sensitivity and specificity of DNA testing for FLN1 mutations and have important functional implications for models of FLN1 protein function in neuronal migration.

• Demelas L et al.
• Incomplete penetrance with normal MRI in a woman with germline mutation of the DCX gene.
• Neurology. 2001; 57: 327-30
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• X-linked isolated lissencephaly sequence (ILS) and subcortical band heterotopia are allelic human disorders associated with mutations of the DCX gene in both familial and sporadic forms. The authors describe a large Sardinian family in which three brothers with ILS have a missense mutation of the DCX gene. Their mother, a nonmosaic carrier, has a normal phenotype and cranial MRI. Skewed X-inactivation in the lymphocytes was also ruled out. This is the first report of an asymptomatic carrier of a DCX mutation likely due to apparent nonpenetrance.

• Gleeson JG
• Classical lissencephaly and double cortex (subcortical band heterotopia): LIS1 and doublecortin.
• Curr Opin Neurol. 2000; 13: 121-5
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• Classical lissencephaly and double cortex are genetic neuronal migration disorders associated with mental retardation and epilepsy. In classical lissencephaly, the six-layered cortex is replaced by a four layered structure lacking normal gyri or sulci. In double cortex, a second layer of cortical neurons underlies a normal cortex. A mutation in LIS1 or doublecortin can lead to either classical lissencephaly or double cortex, but because LIS1 is autosomal and doublecortin is X-linked (on the X chromosome), the disease inheritance pattern and risk of recurrence for the two genes are distinct. Mutation analysis for LIS1 and doublecortin is essential in determining the etiology of the disease in patients and may be helpful in determining the recurrence risk in families.

• Orrico A et al.
• MECP2 mutation in male patients with non-specific X-linked mental retardation.
• FEBS Lett. 2000; 481: 285-8
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• In contrast to the preponderance of affected males in families with X-linked mental retardation, Rett syndrome (RTT) is a neurological disorder occurring almost exclusively in females. The near complete absence of affected males in RTT families has been explained by the lethal effect of an X-linked gene mutation in hemizygous affected males. We report here on a novel mutation (A140V) in the MECP2 gene detected in one female with mild mental retardation. In a family study, the A140V mutation was found to segregate in the affected daughter and in four adult sons with severe mental retardation. These results indicate that MECP2 mutations are not necessarily lethal in males and that they can be causative of non-specific X-linked mental retardation.

• Haque J, Boger S, Li J, Duncan SA
• The murine Pes1 gene encodes a nuclear protein containing a BRCT domain.
• Genomics. 2000; 70: 201-10
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• Pescadillo was originally identified in the zebrafish Danio rerio as a site of a retrovirus-insertion mutation that caused severe defects during embryogenesis. In particular, growth of the fetal zebrafish liver was significantly affected by loss of pescadillo function. To begin to understand the role of pescadillo during mammalian hepatogenesis we identified the murine homologue of pescadillo and named it Pes1. A single gene localized to chromosome 11 on the mouse genome encodes Pes1. Although Pes1 mRNA was detected in all tissues examined it was present at the highest levels in both adult and fetal liver. Analysis of the predicted amino acid sequence of Pes1 found it to contain a BRCT domain, which has previously been found in several proteins involved in cell-cycle checkpoints and DNA repair. Consistent with a putative role in these processes we found that when recombinant Pes1 protein was expressed in HepG2 cells it localized to the nucleus.

• Fukami M et al.
• A member of a gene family on Xp22.3, VCX-A, is deleted in patients with X-linked nonspecific mental retardation.
• Am J Hum Genet. 2000; 67: 563-73
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• X-linked nonspecific mental retardation (MRX) has a frequency of 0.15% in the male population and is caused by defects in several different genes on the human X chromosome. Genotype-phenotype correlations in male patients with a partial nullisomy of the X chromosome have suggested that at least one locus involved in MRX is on Xp22.3. Previous deletion mapping has shown that this gene resides between markers DXS1060 and DXS1139, a region encompassing approximately 1.5 Mb of DNA. Analyzing the DNA of 15 males with Xp deletions, we were able to narrow this MRX critical interval to approximately 15 kb of DNA. Only one gene, VCX-A (variably charged, X chromosome mRNA on CRI-S232A), was shown to reside in this interval. Because of a variable number of tandem 30-bp repeats in the VCX-A gene, the size of the predicted protein is 186-226 amino acids. VCX-A belongs to a gene family containing at least four nearly identical paralogues on Xp22.3 (VCX-A, -B, -B1, and -C) and two on Yq11.2 (VCY-D, VCY-E), suggesting that the X and Y copies were created by duplication events. We have found that VCX-A is retained in all patients with normal intelligence and is deleted in all patients with mental retardation. There is no correlation between the presence or absence of VCX-B1, -B, and VCX-C and mental status in our patients. These results suggest that VCX-A is sufficient to maintain normal mental development.

• Raynaud M et al.
• Systematic analysis of X-inactivation in 19XLMR families: extremely skewed profiles in carriers in three families.
• Eur J Hum Genet. 2000; 8: 253-8
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• It has been demonstrated in several X-linked disorders, both with and without mental retardation, that the X-inactivation process plays a significant role in the expression of X-linked diseases in females. Moreover, in some disorders extremely skewed inactivation of the X chromosome is constant in carriers, and this is thought to result from a proliferation or a survival advantage for cells expressing the normal allele at this locus over cells expressing the mutated allele. X-linked mental retardation (XLMR) is heterogeneous, and cloning and characterization of the mutated genes are in progress. XLMR can be expressed in carrier females but often with milder manifestations. We report the systematic study of the X-inactivation profile of obligate carriers and other females in 19 multiplex XLMR pedigrees, using leucocyte-extracted DNA. Extremely skewed profiles were observed in carriers in three of 19 families.

• Laugier-Anfossi F, Villard L
• Molecular characterization of a new human T-box gene (TBX22) located in xq21.1 encoding a protein containing a truncated T-domain.
• Gene. 2000; 255: 289-96
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• We are conducting a systematic transcriptional mapping of the Xq12-q21 region of the human X chromosome in order to identify new genes potentially involved in X-linked mental retardation phenotypes. In silico analysis using the sequence of the genomic clones originating from this region of the human X chromosome allowed us to characterize a new gene belonging to the T-box family of transcriptional regulators. These genes were shown to be critical for proper development of both vertebrates and invertebrates. We show here that this new gene, called TBX22, is composed of seven exons spanning 8.7 kilobases of genomic DNA in Xq21.1. The TBX22 mRNA is 2099 base pairs long and encodes a 400-amino-acids protein containing a T-domain in its NH(2)-terminal region which has the unique feature of missing 20 amino-acids relative to the other known T-domains. TBX22 transcripts were exclusively found in a human fetal cDNA library and no homologous gene could be detected in the mouse genome. In addition, phylogenetic studies performed using all the known T-domain-containing proteins show that TBX22 is not directly related to any of them. These data indicate that TBX22 may be the first identified member of a new family of T-domain-containing proteins.

• Fryns JP et al.
• 9th international workshop on fragile X syndrome and X-linked mental retardation.
• Am J Med Genet. 2000; 94: 345-60

• Hamel BC, Chiurazzi P, Lubs HA
• Syndromic XLMR genes (MRXS): update 2000.
• Am J Med Genet. 2000; 94: 361-3

• Taylor Clelland CL, Levy B, McKie JM, Duncan AM, Hirschhorn K, Bancroft C
• Cloning and characterization of human PREB; a gene that maps to a genomic region associated with trisomy 2p syndrome.
• Mamm Genome. 2000; 11: 675-81
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• We have isolated the human homolog of a novel rodent gene that may be involved in the regulation of pituitary gene transcription. The human PREB gene encodes a predicted protein of 417 amino acids, exhibiting several sequences characteristic of the WD-motif protein family. PREB transcripts were detected in every human fetal and adult tissue examined, although a great variation in levels of expression was observed. PREB was mapped to human Chromosome 2p23, a region of the genome associated with partial trisomy 2p syndrome. Although variable, the common duplication phenotype includes facial abnormalities, skeletal defects, growth and mental retardation, congenital heart and neural tube defects, and abnormalities of the genitalia. We propose that PREB has a role during human development and that abnormal dosage of this transcription factor may be involved in some of the developmental abnormalities observed in patients with partial trisomy 2p.

• Buchner G et al.
• Identification of a new EGF-repeat-containing gene from human Xp22: a candidate for developmental disorders.
• Genomics. 2000; 65: 16-23
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• Epidermal growth factor (EGF) repeat-containing proteins constitute an expanding family of proteins involved in several cellular activities such as blood coagulation, fibrinolysis, cell adhesion, and neural and vertebrate development. By using a bioinformatic approach, we have identified a new member of this family named MAEG (MAM- and EGF-containing gene; HGMW-approved gene symbol and gene name). Sequence analysis indicates that MAEG encodes a secreted protein characterized by the presence of five EGF repeats, three of which display a Ca(2+)-binding consensus sequence. In addition, a MAM domain is also present at the C-terminus of the predicted protein product. The human and murine full-length cDNAs were identified and mapped to human Xp22 and to the mouse syntenic region. Northern analysis indicates that MAEG is expressed early during development. Taken together, these data render MAEG a candidate for human and murine developmental disorders.

• Chelly J
• MRX review.
• Am J Med Genet. 2000; 94: 364-6

• Taylor KR, Holzer AK, Bazan JF, Walsh CA, Gleeson JG
• Patient mutations in doublecortin define a repeated tubulin-binding domain.
• J Biol Chem. 2000; 275: 34442-50
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• Doublecortin (DCX) missense mutations are found in two clusters in patients with defective cortical neuronal migration. Although DCX can function as a microtubule-associated protein (MAP), the potential relationship between its MAP activity and neuronal migration is not understood. Here we show that the two clusters of patient mutations precisely define an internal tandem repeat. Each repeat alone binds tubulin, whereas neither repeat is sufficient for co-assembly with microtubules. The two tandem repeats are sufficient to mediate microtubule polymerization, and representative patient missense mutations lead to impaired polymerization both in vitro and in vivo as well as impaired microtubule stabilization. Furthermore, each repeat is predicted to have the secondary structure of a beta-grasp superfold motif, a motif not found in other MAPs. The patient mutations are predicted to disrupt the structure of the motif, suggesting that the motif may be critical for the DCX-tubulin interaction. These data provide both genetic and biochemical evidence that the interaction of DCX with microtubules is dependent upon this novel repeated tubulin-binding motif.

• Zhai L, Mu J, Zong H, DePaoli-Roach AA, Roach PJ
• Structure and chromosomal localization of the human glycogenin-2 gene GYG2.
• Gene. 2000; 242: 229-35
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• Glycogenin-2 is one of two self-glucosylating proteins involved in the initiation phase of the synthesis of the storage polysaccharide glycogen. Cloning of the human glycogenin-2 gene, GYG2, has revealed the presence of 11 exons and a gene of more than 46 kb in size. The structure of the gene explains much of the observed diversity in glycogenin-2 cDNA sequences as being due to alternate exon usage. In some cases, there is variation in the splice junctions used. Over regions of protein sequence similarity, the GYG2 gene structure is similar to that of the other glycogenin gene, GYG. A genomic GYG2 clone was used to localize the gene to Xp22.3 by fluorescence in-situ hybridization. Localization close to the telomere of the short arm of the X chromosome is consistent with mapping information obtained from glycogenin-2 STS sequences. Glycogenin-2 maps between the microsatellite anchor markers AFM319te9 (DXS7100) and AFM205tf2 (DXS1060), and its 3' end is 34.5 kb from the 3' end of the arylsulphatase gene ARSD. GYG2 is outside the pseudoautosomal region PAR1 but still in a region of X-Y shared genes. As is true for several other genes in this location, an inactive remnant of GYG2, consisting of exons 1-3, may be present on the Y chromosome.

• Aigner L, Fluegel D, Dietrich J, Ploetz S, Winkler J
• Isolated lissencephaly sequence and double-cortex syndrome in a German family with a novel doublecortin mutation.
• Neuropediatrics. 2000; 31: 195-8
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• Isolated Lissencephaly Sequence (ILS) and Double-Cortex Syndrome (DC) are neuronal heterotopias caused by developmental defects in neuronal precursor cell migration. We report on the clinical and genetic assessment of a German pedigree with DCIILS. Affected males showed clinical symptoms typical of lissencephaly, i.e. seizures, severe mental retardation and extensive physical disability starting in the early postnatal period. Females, however, displayed a milder phenotype with epileptic seizures being the only clinical symptom of note. The MR imaging of a male ILS patient showed a smooth cortex with pachygyria, hydrocephalus and a diffuse, broad distribution of grey matter throughout the brain. In the affected female, a double cortex syndrome in the form of a subcortical bilateral band of grey matter was evident by MR imaging. The molecular and genetic basis of DC/ILS is associated with mutations in the X-linked doublecortin gene (DCX). The genetic assessment of the family revealed a novel missense mutation 211 G-->T in DCX exon 2 in affected family members. This mutation cosegregated with the clinical symptoms and resulted in a non-conservative amino acid substitution A71S. DCX is a microtubule-associated phosphoprotein and mutations in DCX might affect cytoskeletal dynamics and the regulation of cell migration.

• Costanzi E, Beccari T, Stinchi S, Bibi L, Hopwood JJ, Orlacchio A
• Gene encoding the mouse sulphamidase: cDNA cloning, structure, and chromosomal mapping.
• Mamm Genome. 2000; 11: 436-9
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• Sulphamidase is an exoglycosidase involved in the degradation of heparan sulfate. Lack of sulphamidase activity leads to the lysosomal storage disorder Mucopolysaccharidosis type IIIA (Sanfilippo type A OMIM No. 252900). At present there are no naturally occurring small animal models of this disease that could be of fundamental importance to study the pathophysiology of the disease and to try therapeutic strategies. Cloning of the mouse gene is an important step to create a mouse model for this common mucopolysaccharidosis. We have isolated and sequenced the gene encoding mouse sulphamidase. Comparison of the deduced amino acid sequences of human and mouse sulphamidase showed 88% identity and 93% similarity. The exon-intron structure of the gene has been determined with the mouse 10-kb gene divided in 8 exons. The mouse sulphamidase gene (Sgsh) was mapped to the distal end of Chromosome (Chr) 11, in a region that is homologous with a segment of human Chr 17 containing the orthologous human gene.

• Ramakers GJ
• Rho proteins and the cellular mechanisms of mental retardation.
• Am J Med Genet. 2000; 94: 367-71
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• The biological basis of mental retardation is poorly understood. Mental retardation is associated with an immature morphology of synaptic spines, structures involved in neurotransmission and memory processes, suggesting that mental retardation is due to a deficiency in neuronal network formation. Recently, several genes involved in X-linked mental retardation (MRX) have been cloned. Investigation of the roles of these genes in neuronal development and function should lead to a better understanding of the cellular mechanisms underlying mental retardation. A significant number of MRX genes is directly involved in signal transduction through Rho proteins. These Rho proteins act as molecular switches which integrate extracellular and intracellular signals to regulate rearrangement of the actin cytoskeleton. Since the actin cytoskeleton mediates neuronal motility and morphogenesis, one can envision how mutations in proteins involved in Rho-dependent signaling result in mental retardation by altering neuronal network formation.

• Langnaese K, Colleaux L, Kloos DU, Fontes M, Wieacker P
• Cloning of Z39Ig, a novel gene with immunoglobulin-like domains located on human chromosome X.
• Biochim Biophys Acta. 2000; 1492: 522-5
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• The cDNA sequence and expression profile of a novel human gene, encoding a new member of the immunoglobulin superfamily, is reported. The gene is localized in the pericentromeric region of human X chromosome between the markers DXS1213 and DXS1194. Abundant expression of transcripts was detected in several human fetal tissues, whereas among adult tissues lung and placenta express highest levels of Z39Ig mRNA.

• Russo S et al.
• Mapping to distal Xq28 of nonspecific X-linked mental retardation MRX72: linkage analysis and clinical findings in a three-generation Sardinian family.
• Am J Med Genet. 2000; 94: 376-82
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• Families with mentally retarded males found to be negative for FRAXA and FRAXE mutations are useful in understanding the genetic basis of X-linked mental retardation. According to the most recent data (updated to 1999), 69 MRX loci have been mapped and 6 genes cloned. Here we report on a linkage study performed on 20 subjects from a 4-generation Sardinian family segregating a non-specific X-linked recessive mental retardation (XLMR)(MRX72) associated with global delay of all psychomotor development. Five of 8 affected males have been tested for mental age, verbal and performance skills and behavioral anomalies; mental impairment ranged from mild to severe. Only minor anomalies were present in the affected subjects. Two-point linkage analysis based on 28 informative microsatellites spanning the whole X chromosome demonstrated linkage between the disorder and markers DXS1073 and F8c in Xq28 (maximum Lod score of 2. 71 at straight theta = 0.00). Multipoint linkage analysis confirmed the linkage with a Z(max) of 3.0 at straight theta = 0.00 at DXS1073 and F8c. Recombination in an affected male at DXS1073 and F8c allowed us to delimit centromerically and telomerically the region containing the putative candidate gene. The region, where MRX72 maps, overlaps that of another MRX families previously mapped to Xq28, two of which harbored mutations in GDI. Involvement of this gene was excluded in our family, suggesting another MRX might reside in Xq28.

• Bohne J et al.
• Expression analysis and mapping of the mouse and human transcriptional regulator CA150.
• Mamm Genome. 2000; 11: 930-3

• Stevenson RE, Abidi F, Schwartz CE, Lubs HA, Holmes LB
• Holmes-Gang syndrome is allelic with XLMR-hypotonic face syndrome.
• Am J Med Genet. 2000; 94: 383-5

• Lossi AM et al.
• Exclusion of nine candidate genes for their involvement in X-linked FG syndrome (FGS1) in three families.
• Am J Med Genet. 2000; 94: 386-8

• Cardoso C et al.
• The location and type of mutation predict malformation severity in isolated lissencephaly caused by abnormalities within the LIS1 gene.
• Hum Mol Genet. 2000; 9: 3019-28
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• Lissencephaly is a cortical malformation secondary to impaired neuronal migration resulting in mental retardation, epilepsy and motor impairment. It shows a severity spectrum from agyria with a severely thickened cortex to posterior band heterotopia only. The LIS1 gene on 17p13.3 encodes a 45 kDa protein named PAFAH1B1 containing seven WD40 repeats. This protein is required for optimal neuronal migration by two proposed mechanisms: as a microtubule-associated protein and as one subunit of the enzyme platelet-activating factor acetylhydrolase. Approximately 65% of patients with isolated lissencephaly sequence (ILS) show intragenic mutations or deletions of the LIS1 gene. We analyzed 29 non-deletion ILS patients carrying a mutation of LIS1 and we report 15 novel mutations. Patients with missense mutations had a milder lissencephaly grade compared with those with mutations leading to a shortened or truncated protein (P = 0.022). Early truncation/deletion mutations in the putative microtubule-binding domain resulted in a more severe lissencephaly than later truncation/deletion mutations (P < 0.001). Our results suggest that the lissencephaly severity in ILS caused by LIS1 mutations may be predicted by the type and location of the mutation. Using a spectrum of ILS patients, we confirm the importance of specific WD40 repeats and a putative microtubule-binding domain for PAFAH1B1 function. We suggest that the small number of missense mutations identified may be due to underdiagnosis of milder phenotypes and hypothesize that the greater lissencephaly severity seen in Miller-Dieker syndrome may be secondary to the loss of another cortical development gene in the deletion of 17p13.3.

• Yoshiura K, Noda Y, Kinoshita A, Niikawa N
• Colocalization of doublecortin with the microtubules: an ex vivo colocalization study of mutant doublecortin.
• J Neurobiol. 2000; 43: 132-9
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• Doublecortin (DCX) plays an important role in neuronal migration and development, and the participation of DCX in neuronal migration has been demonstrated by intensive mutational analysis for patients with X-linked or sporadic lissencephaly, and/or subcortical laminar heterotopia. Although a previous search for protein similarity showed that DCX has a region homologous to the putative Ca(2+)/calmodulin-dependent protein kinase, the function of the DCX gene (DCX) has remained unknown. We show here that mouse DCX colocalizes with the microtubules and provide evidence that its conformational structure is important for its subcellular localization by means of mutant doublecortin expression study. The results of our study may suggest that the cytoskeleton involving DCX mediates the neuronal migration during brain development.

• Jin H, Gardner RJ, Viswesvaraiah R, Muntoni F, Roberts RG
• Two novel members of the interleukin-1 receptor gene family, one deleted in Xp22.1-Xp21.3 mental retardation.
• Eur J Hum Genet. 2000; 8: 87-94
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• X-linked mental retardation is estimated to affect approximately 1 in 600 males. Although numerous genes responsible for syndromic mental retardation have been identified, the study of non-syndromic mental retardation suffers from intrinsic issues of genetic heterogeneity. During the investigation of three brothers with a contiguous gene deletion syndrome of Becker muscular dystrophy, glycerol kinase deficiency, congenital adrenal hypoplasia, and mental retardation, we found their dystrophin gene to be fused tail-to-tail with a gene encoding a novel member of the interleukin-1 receptor family, IL1RAPL1. This gene has a close relative in Xq22, which we call IL1RAPL2. Both IL1RAPL1 and IL1RAPL2 have novel C-terminal sequences not present in other related proteins, and are encoded by very large genes. The 1.8-megabase deletion in these patients removes not only the last exon of the dystrophin gene, the entire glycerol kinase and DAX-1 genes, and the MAGE-B gene cluster, but also three exons encoding the intracellular signalling domain of IL1RAPL1. The literature contains multiple reports of patients with non-syndromic mental retardation in association with an Xp22.1-Xp21.3 microdeletion of a marker which lies within the IL1RAPL1 gene. The gene is also wholly or partially deleted in patients with mental retardation as part of a contiguous deletion syndrome. We suggest that IL1RAPL1, and perhaps IL1RAPL2, are strong candidates for X-linked non-syndromic mental retardation loci, and that molecules resembling IL-1 and IL-18 play a role in the development or function of the central nervous system.

• Sakamoto M, Ono J, Okada S, Nakamura Y, Kurahashi H
• Genetic alteration of the DCX gene in Japanese patients with subcortical laminar heterotopia or isolated lissencephaly sequence.
• J Hum Genet. 2000; 45: 167-70
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• We examined mutations of the doublecortin (DCX) gene, which is responsible for X-linked subcortical laminar heterotopia (SCLH) and lissencephaly, in eight unrelated Japanese patients, four with SCLH and four with isolated lissencephaly sequence (ILS). Polymerase chain reaction (PCR) disclosed a deletion of part of the DCX gene in one male ILS patient. Single-strand conformational polymorphism analysis and subsequent sequence analysis were carried out in the remaining seven patients. One male ILS patient had a nonsense mutation in exon V, which would result in premature termination of the gene product. One female SCLH patient had a missense mutation in exon IV. Our results indicate that in the Japanese, as has been seen elsewhere, abnormality of the DCX gene is the common cause of SCLH and ILS.

• van Kuilenburg AB, Meinsma R, Vreken P, Waterham HR, van Gennip AH
• Identification of a cDNA encoding an isoform of human CTP synthetase.
• Biochim Biophys Acta. 2000; 1492: 548-52
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• A full-length cDNA clone encoding an isoform of human CTP synthetase (type II) was isolated. A 1761-nucleotide open reading frame which corresponds to a protein of 586 amino acids with a predicted molecular mass of 65678 Da was identified. The predicted protein sequence showed 74% identity with the translation product of a previously identified human CTP synthetase cDNA clone (type I). The function of the human cDNA encoding type II CTP synthetase was verified by successful complementation of the cytidine-requiring CTP synthetase deficient mutant JF618 of Escherichia coli. The gene encoding type II CTP synthetase has been localized on chromosome Xp22.

• Gleeson JG et al.
• Genetic and neuroradiological heterogeneity of double cortex syndrome.
• Ann Neurol. 2000; 47: 265-9
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• Mutations in the X-linked doublecortin gene appear in many sporadic cases of double cortex (DC; also known as subcortical band heterotopia), a neuronal migration disorder causing epilepsy and mental retardation. The purpose of this study was to examine why a significant percentage of sporadic DC patients had been found not to harbor doublecortin mutations and to determine whether clinical features or magnetic resonance imaging scan appearance could distinguish between patients with and without doublecortin mutations. Magnetic resonance imaging scan analysis differentiated patients into the following four groups: anterior biased/global DC with doublecortin mutation (16 of 30; 53%), anterior biased/global DC without mutation (8 of 30; 27%), posterior biased DC without mutation (3 of 30; 10%), and limited/unilateral DC without mutation (3 of 30; 10%). The presence of these atypical phenotypes suggests that other genetic loci or mosaicism at the doublecortin locus may be responsible for this diversity of DC cases.

• Seki N, Azuma T, Yoshikawa T, Masuho Y, Muramatsu M, Saito T
• cDNA cloning of a new member of the Ras superfamily, RAB9-like, on the human chromosome Xq22.1-q22.3 region.
• J Hum Genet. 2000; 45: 318-22
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• Members of the RAB protein family regulate vesicular trafficking and reside in specific intercellular compartments. A new member of the RAB family was identified through a public database search, and its full-length cDNA was isolated from a human fetal brain cDNA library. The predicted protein product of the gene consists of 201 amino acid residues, and the protein has 86% similarity to human RAB9 at the amino acid level. We designated the new gene RAB9-like. Northern blot analysis showed that the gene was transcribed ubiquitously in various human tissues. A database search revealed that the gene is divided into three exons and spans approximately 7.2kb of the genome DNA of chromosome Xq22.1-q22.3 region.

• DeLisi LE et al.
• Investigation of a candidate gene for schizophrenia on Xq13 previously associated with mental retardation and hypothyroidism.
• Am J Med Genet. 2000; 96: 398-403
• Display abstract

• Weak support for linkage of schizophrenia to proximal Xq has previously been reported. In addition, an increased prevalence of thyroid disorder has been noted in families of individuals with schizophrenia. Recently, a gene mapped to Xq13 termed HOPA has been found to be associated with mental retardation, hypothyroidism, and depression and to function as a coactivator for the thyroid receptor. We therefore examined the HOPA gene in a group of 111 probands from a larger cohort of multiplex families with schizophrenia, several of whom (n = 53) also had a family history of hypothyroidism. Four males and two females were found with an alteration in exon 42 of the HOPA gene compared with 8/492 males and 18/471 females (942 X chromosomes) compared with consecutively screened newborns (chi(2) = 3.92, P < 0.05). However, when available family members of each of the probands with an exon 42 variation were subsequently screened, the mutation did not segregate with schizophrenia in three of five families, although all 6 probands with an exon 42 variation did have hypothyroidism in either themselves (n = 3) or their mothers (n = 3) (P < 0.008). These findings replicate prior findings demonstrating an association between HOPA polymorphisms and hypothyroidism. In addition, the increased frequency of HOPA variants in this population may also provide a genetic basis for the familial association of thyroid disease and schizophrenia.

• Lappalainen I et al.
• Structural basis for SH2D1A mutations in X-linked lymphoproliferative disease.
• Biochem Biophys Res Commun. 2000; 269: 124-30
• Display abstract

• X-linked lymphoproliferative disease (XLP) is a rare and severe immune deficiency, characterized by abnormal immune responses to the Epstein-Barr virus. Recently, the gene responsible for XLP, SH2D1A, has been identified and shown to code for a small cytoplasmic protein with an SH2 domain that interacts with SLAM and 2B4, two receptorial molecules involved in signal transduction in T and NK cells, respectively. A variety of SH2D1A gene mutations have been reported thus far in XLP males. Here we describe a single-strand conformation polymorphism assay for mutation analysis in XLP. Four novel patients with SH2D1A mutations are described. These mutants, and the others previously reported in the literature, have been included in a Registry (SH2D1Abase) that is fully accessible on the World Wide Web. A three-dimensional model of the SH2 domain of the SH2D1A protein has been developed, based on homology with other SH2 domains. The structural consequences of disease-causing SH2D1A mutations are discussed.

• Jin DY, Jeang KT
• Isolation of full-length cDNA and chromosomal localization of human NF-kappaB modulator NEMO to Xq28.
• J Biomed Sci. 1999; 6: 115-20
• Display abstract

• NEMO is an essential component of the IkappaB kinase complex. Others have shown that expression of mouse NEMO can complement the lack of responsiveness to NF-kappaB stimuli in two NEMO-deficient cell lines. Here we report the isolation of a full-length human NEMO cDNA. Virtual translation of human NEMO cDNA predicts a 48-kD coiled-coil protein which shares 87.9% identity and 90.5% similarity with the mouse homolog. By sequence alignment, we mapped the human NEMO gene to chromosome Xq28. We note that the NEMO and the G6PD (glucose-6-phosphate dehydrogenase) loci are arranged in a head-to-head orientation separated by no more than 800 bp. This map location is further supported by the sequence of an alternatively spliced variant of human NEMO mRNA. Thus, human NEMO is an X-linked gene closely adjacent to the G6PD locus.

• Gaines P, Woodard CT, Carlson JR
• An enhancer trap line identifies the Drosophila homolog of the L37a ribosomal protein.
• Gene. 1999; 239: 137-43
• Display abstract

• A gene identified from an enhancer trap screen is shown to encode the Drosophila melanogaster homolog of the L37a ribosomal protein. The predicted 92 amino-acid sequence of this protein is 78% identical to mammalian L37a proteins, and contains a conserved Cys-X2 Cys-X14-Cys-X2-Cys zinc finger motif that may be involved in interactions with ribosomal RNA. The Drosophila L37a homolog is a single copy gene comprised of four exons and is ubiquitously expressed throughout the animal. Cytological localization reveals that Drosophila L37a maps to position 25C1-3, very near the previously described Minute mutation M(2)25C.

• Allen KM, Walsh CA
• Genes that regulate neuronal migration in the cerebral cortex.
• Epilepsy Res. 1999; 36: 143-54
• Display abstract

• Malformations of cortical development are increasingly recognized as causes of mental retardation and epilepsy. However, little is known about the molecular and biochemical signals that control the proliferation, migration, and organization of the cells involved in normal cerebral cortical development. Analysis of genes required for cortical development will help elucidate the pathogenesis of some epilepsies. In humans, two striking examples of abnormal cortical development, with varying degrees of epilepsy and mental retardation, are 'double cortex' and lissencephaly. Double cortex (DC), also known as subcortical band heterotopia, shows an abnormal band of neurons in the white matter underlying a relatively normal cortex. In pedigrees, DC often occurs in females, whereas affected males show more severe lissencephaly (XLIS), i.e. an abnormally thick cortex with decreased or absent surface convolutions. We and others have identified a novel brain specific gene, doublecortin, that is mutated in Double Cortex/X-linked lissencephaly (DC/XLIS) patients. Although the cellular function of doublecortin (DCX) is unknown, sequence analysis reveals a cytoplasmic protein with potential MAP kinase phosphorylation sites, as well as a site that is likely to be phosphorylated by c-Abl, suggesting that doublecortin functions as an intracellular signaling molecule critical for the migration of developing neurons. Interestingly, the scrambler mouse mutant demonstrates abnormal lamination with some similarity to lissencephaly and reflects a mutation in the murine homolog of the Drosophila disabled gene, mdab1, which binds c-Abl. Although a direct interaction between doublecortin and mDab1 has not been demonstrated, it is plausible that these two proteins may be part of a common signaling pathway. Therefore, abnormalities in signal transduction may be an underlying mechanism for the neuronal migration defects in DC/XLIS and the scrambler mouse, but further research is necessary to determine how such abnormalities give rise to cortical malformations and epilepsy.

• Agulnik AI, Longepied G, Ty MT, Bishop CE, Mitchell M
• Mouse H-Y encoding Smcy gene and its X chromosomal homolog Smcx.
• Mamm Genome. 1999; 10: 926-9

• Shrimpton AE, Daly KM, Hoo JJ
• Mapping of a gene (MRXS9) for X-linked mental retardation, microcephaly, and variably short stature to Xq12-q21.31.
• Am J Med Genet. 1999; 84: 293-9
• Display abstract

• Three boys from two families were identified as having a syndrome of X-linked mental retardation (XLMR) with microcephaly and short stature, clinically resembling Renpenning syndrome but with normal size of testicles in affected men. When the effort to map the gene for the above condition was initiated, it was realized that the two families were actually related to each other. Over 50 polymorphic markers of known locations along the X chromosome were scored in this family in a study to map the disease gene. Nine affected and four unaffected males were genotyped to produce a maximum LOD score of 4.42 at zero recombination with markers in proximal Xq. The results indicate that the gene responsible for this disorder is located in the cytogenetic Xq12 to Xq21.31 interval of the X chromosome within a section of chromosome of about 17 cM between the AR and DXS1217 loci over some 25 mb. Since the gene for the X-linked mental retardation from the original Saskatchewan family described by Renpenning [Renpenning et al., 1962: Can Med Assoc J 87:954-956; Fox and Gerrard, 1980: Am J Med Genet 7:491-495] was recently mapped to a different nonoverlapping region [Stevenson et al., 1998: Am J Hum Genet 62:1092-1101] this would appear to be a separate disorder.

• Neri G, Chiurazzi P
• X-linked mental retardation.
• Adv Genet. 1999; 41: 55-94

• Christianson AL et al.
• X linked severe mental retardation, craniofacial dysmorphology, epilepsy, ophthalmoplegia, and cerebellar atrophy in a large South African kindred is localised to Xq24-q27.
• J Med Genet. 1999; 36: 759-66
• Display abstract

• To date over 150 X linked mental retardation (XLMR) conditions have been documented. We describe a five generation South African family with XLMR, comprising 16 affected males and 10 carrier females. The clinical features common to the 16 males included profound mental retardation (100%), mutism despite apparently normal hearing (100%), grand mal epilepsy (87.5%), and limited life expectancy (68.8%). Of the four affected males examined, all had mild craniofacial dysmorphology and three were noted to have bilateral ophthalmoplegia and truncal ataxia. Three of 10 obligate female carriers had mild mental retardation. Cerebellar and brain stem atrophy was shown by cranial imaging and postmortem examination. Linkage analysis shows the gene to be located between markers DXS424 (Xq24) and DXS548 (Xq27.3), with a maximum two point lod score of 3.10.

• Villard L et al.
• Evaluation of a mutation screening strategy for sporadic cases of ATR-X syndrome.
• J Med Genet. 1999; 36: 183-6
• Display abstract

• We report on the evaluation of a strategy for screening for XNP/ATR-X mutations in males with mental retardation and associated dysmorphology. Because nearly half of the mutations in this gene reported to date fall into a short 300 bp region of the transcript, we decided to focus in this region and to extend the mutation analysis to cases with a negative family history. This study includes 21 mentally retarded male patients selected because they had severe mental retardation and a typical facial appearance. The presence of haemoglobin H or urogenital abnormalities was not considered critical for inclusion in this study. We have identified six mutations which represents a mutation detection rate of 28%. This figure is high enough for us to propose this strategy as a valid first level of screening in a selected subset of males with mental retardation. This approach is simple, does not require RNA preparation, does not involve time consuming mutation detection methods, and can thus be applied to a large number of patients at a low cost in any given laboratory.

• Shimizu K et al.
• The autocrine motility factor receptor gene encodes a novel type of seven transmembrane protein.
• FEBS Lett. 1999; 456: 295-300
• Display abstract

• Autocrine motility factor receptor (AMFR) is a cell surface glycoprotein of molecular weight 78,000 (gp78), mediating cell motility signaling in vitro and metastasis in vivo. Here, we cloned the full-length cDNAs for both human and mouse AMFR genes. Both genes encode a protein of 643 amino acids containing a seven transmembrane domain, a RING-H2 motif and a leucine zipper motif and showed a 94.7% amino acid sequence identity to each other. Analysis of the amino acid sequence of AMFR with protein databases revealed no significant homology with all known seven transmembrane proteins, but a significant structural similarity to a hypothetical protein of Caenorhabditis elegans, F26E4.11. Thus, AMFR is a highly conserved gene which encodes a novel type of seven transmembrane protein.

• Kato M et al.
• A novel mutation of the doublecortin gene in Japanese patients with X-linked lissencephaly and subcortical band heterotopia.
• Hum Genet. 1999; 104: 341-4
• Display abstract

• The doublecortin (DCX) gene was recently found to be involved in patients with X-linked lissencephaly and subcortical band heterotopia or double cortex syndrome. We have studied the coding regions of the DCX gene in 11 Japanese patients with cortical dysplasia and have identified three different mutations (R186C in exon 3, R272X and R303X in exon 5) in four sporadic female cases. R272X, which has been detected in two unrelated cases, is a novel mutation. Although the number of cases studied remains limited, exon 5 may be a common mutational site in Japanese patients in contrast to many previous reports concerning exons 2 and 3.

• Bruyere H, Lewis ME, Wood S, MacLeod P, Langlois S
• Increasing evidence for a new X-linked mental retardation/epilepsy gene localized to Xp21.3-Xp22.1.
• Am J Med Genet. 1999; 86: 401-401

• Mears AJ et al.
• Protein-truncation mutations in the RP2 gene in a North American cohort of families with X-linked retinitis pigmentosa.
• Am J Hum Genet. 1999; 64: 897-900

• Illarioshkin SN et al.
• Studies of the candidate genes in X-linked congenital cerebellar hypoplasia.
• J Neurol. 1999; 246: 1177-80
• Display abstract

• A gene for X-linked congenital cerebellar hypoplasia was recently localized to chromosome Xp11.21-q24. This region comprises several brain-specific genes responsible for various neurological disorders, including the proteolipid protein (PLP), doublecortin, and PAK3 genes. We screened these genes for mutations in patients with X-linked congenital cerebellar hypoplasia and found no pathogenic nucleotide changes or gene dose alterations. These findings allow the ruling out of PLP, doublecortin, and PAK3 as the disease-causing genes in this hereditary neurological syndrome.

• Chelly J
• Breakthroughs in molecular and cellular mechanisms underlying X-linked mental retardation.
• Hum Mol Genet. 1999; 8: 1833-8
• Display abstract

• Although genetic causes of X-linked mental retardation (XLMR) are heterogeneous and complex, recent concerted actions between physicians and biologists have allowed some major difficulties to be overcome and led to the identification of an increasing number of genes involved in these conditions. Indeed, over the past 2 years significant progress has been made in understanding the molecular basis underlying not only XLMR, where there are distinguishing phenotypic or genetic markers (syndromal forms of XLMR), but also non-specific (or idiopathic) mental retardation (MRX). Recent breakthroughs have shown that genes responsible for these latter conditions encode for proteins involved in signalling pathways which regulate cytoskeleton organization, synaptic vesicle transport and, maybe, other cellular functions. Also, they suggest a provacative picture that conceptualizes MRX as disorders resulting from a dysfunctioning of genes required for processes such as the remodelling, establishment and stabilization of connections between neuronal cells. Such processes are crucial for the development of intellectual and cognitive functions. As these functions begin to evolve mainly in post-natal stages through contact with diverse stimuli and environments, a potential therapeutic approach would be the development of drugs that target cellular signalling pathways shown to be implicated in MRX.

• Bieganski T, Dawydzik B, Kozlowski K
• Spondylo-epimetaphyseal dysplasia: a new X-linked variant with mental retardation.
• Eur J Pediatr. 1999; 158: 809-14
• Display abstract

• A new X-linked variant of spondylo-epimetaphyseal dysplasia with distinctive phenotype and severe mental retardation in three boys of one family is reported. The children were normal at birth. After several months of normal development progressive physical disability and slow mental deterioration were observed. Extensive biochemical tests were normal. CONCLUSION: These patients represent a new form of X-linked spondylo-epimetaphyseal dysplasia.

• Tackels D, Schwartz CE, Carpenter NJ, Miles JH
• Refined gene localization for the Miles-Carpenter syndrome (MCS)
• Am J Med Genet. 1999; 85: 221-2

• Carrie A et al.
• Construction of a highly annotated cosmid contig spanning 550Kb within the X-linked nonspecific mental retardation candidate region at Xp21.3-22.1.
• Am J Med Genet. 1999; 85: 252-4

• des Portes V et al.
• X-linked nonspecific mental retardation (MRX) linkage studies in 25 unrelated families: the European XLMR consortium.
• Am J Med Genet. 1999; 85: 263-5

• Hane B, Stevenson RE, Arena JF, Lubs HA, Simensen RJ, Schwartz CE
• Gene for apparently nonsyndromic X-linked mental retardation (MRX32) maps to an 18-Mb region of Xp21.2-p22.
• Am J Med Genet. 1999; 85: 271-5
• Display abstract

• We studied a family with 11 males having X-linked mental retardation (XLMR) using microsatellite markers. Aside from the mental retardation, the affected males do not appear to differ from their unaffected brothers or uncles. The gene for this XLMR condition has been linked to DXS451 in Xp22.13 with a lod score of 5.18 at straight theta = 0. Recombination was detected at DXS992 (Xp21.3) and DXS1053 (Xp22.2), thereby defining the limits of the localization. This family is considered to have nonsyndromic XLMR and has been assigned the designation MRX32.

• Tackels D, Schwartz CE, Thibodeau SN, Michels VV
• Refined gene localization for MRX7.
• Am J Med Genet. 1999; 85: 288-9

• Hamel BC et al.
• Four families (MRX43, MRX44, MRX45, MRX52) with nonspecific X-linked mental retardation: clinical and psychometric data and results of linkage analysis.
• Am J Med Genet. 1999; 85: 290-304
• Display abstract

• Four families are described in which mental retardation segregates in an X-linked fashion. Mental retardation was the only consistent clinical finding in all affected males. The degree of retardation varied from mild to profound both between and within families. Linkage analysis localized the genetic defect of MRX43 to Xp22. 31-p21.2, MRX44 to Xp11.3-p11.21, MRX45 to Xp11.3-p11.21, and MRX52 to Xp11.21-q21.33 with LOD scores of >2 at straight theta = 0.0 in all four families.

• Tackels D, Schwartz CE
• Refined gene localization for MRX8.
• Am J Med Genet. 1999; 85: 309-10

• Mizuguchi M, Qin J, Yamada M, Ikeda K, Takashima S
• High expression of doublecortin and KIAA0369 protein in fetal brain suggests their specific role in neuronal migration.
• Am J Pathol. 1999; 155: 1713-21
• Display abstract

• The X-linked subcortical laminar heterotopia and lissencephaly syndrome is a disorder of neuronal migration caused by a mutation in XLIS, a recently cloned gene on chromosome Xq22.3-q23. The predicted protein product for XLIS, doublecortin (DC), shows high homology to a putative calcium calmodulin-dependent kinase, KIAA0369 protein (KI). Here we identified DC and KI in the brains of human and rat fetuses by immunochemical and immunohistochemical means. In this study, Western blotting demonstrated that both DC and KI are specific to the nervous system and are abundant during the fetal period, around 20 gestational weeks in humans and embryonic days 17 to 20 in rats. Immunostaining of the developing neocortex disclosed localization of DC and KI immunoreactivities in neuronal cell bodies and processes in the zones of ongoing neuronal migration. Although KI showed a somewhat wider distribution than DC, the temporal and spatial patterns of their expression were similar. These results suggest that DC and KI participate in a common signaling pathway regulating neuronal migration.

• FitzGerald KT, Diaz MO
• MLL2: A new mammalian member of the trx/MLL family of genes.
• Genomics. 1999; 59: 187-92
• Display abstract

• We have identified a gene at chromosome band 19q13.1, which is closely related to MLL. MLL is located in a region of chromosome 11q23 that has partial synteny with chromosome 19q. We have named this gene at 19q13.1, MLL2. MLL2 encodes a protein that exhibits a high level of similarity to MLL over several important protein domains. MLL2 is also ubiquitously expressed among adult human tissues, as is MLL. MLL is a homologue of the Drosophila gene trithorax (trx), which encodes a regulator of homeotic gene expression. MLL is involved in chromosome rearrangements associated with leukemia in mammals. However, no MLL2 rearrangements associated with leukemia have been recorded.

• Zhang M et al.
• Cloning and mapping of the XRN2 gene to human chromosome 20p11.1-p11.2.
• Genomics. 1999; 59: 252-4
• Display abstract

• The Dhm1 gene is the mouse homologue of the dhp1(+) gene of Schizosaccharomyces pombe, which is involved in homologous recombination and RNA metabolism, such as RNA synthesis and RNA trafficking, in S. pombe. Complementation analysis showed the Dhm1 gene on a multicopy plasmid can rescue the temperature-sensitivity mutation of dhp1(ts) and the lethality of the dhp1 null mutation. This finding suggests that Dhm1 has a function in mouse similar to that of dhp1(+). The human homologue of this gene, XRN2, has been identified. A 3.6-kb transcript of XRN2 was detected in 16 tissues examined and was more abundant in testis. By radiation hybrid panel mapping, the XRN2 gene was localized to chromosome 20p11.1-p11.2 between markers D20S180 and D20S871.

• Gehrig AE, Warneke-Wittstock R, Sauer CG, Weber BH
• Isolation and characterization of the murine X-linked juvenile retinoschisis (Rs1h) gene.
• Mamm Genome. 1999; 10: 303-7
• Display abstract

• X-linked juvenile retinoschisis (RS) is a vitreoretinal degeneration affecting only males. Recently, the RS1 gene underlying this common cause of early vision loss was identified and shown to encode a 224-amino acid precursor protein including a 23-residue leader sequence as well as a highly conserved discoidin motif at the C-terminus. Functional studies in other proteins with discoidin motifs have implicated this domain in phospholipid binding and cell-cell interactions on membrane surfaces. Thus, similar functional properties may exist for RS1 and may be related to the histopathological findings in RS. In order to further pursue the pathophysiology of RS and to understand RS1 function in early eye development, we now report the identification and characterization of the complete murine Rs1h gene. The full-length Rs1h cDNA was isolated by RT-PCR with degenerate oligonucleotide primers designed from human RS1 cDNA sequences. Subsequently, the exon/intron structure was determined in genomic DNA from mouse strain 129/SvJ. We show that human and murine RS1 coding sequences, exon/intron boundaries, as well as retina-specific expression, are highly conserved between the two species. The conceptual human and murine protein sequences reveal 96% amino acid identity with no amino acid changes within the discoidin domain. In addition, alignment of 5'-flanking sequences upstream of the human and mouse RS1 translation initiation sites identified putative binding sites for several transcription factors including CRX, a homeodomain transcription factor known to activate the transcription of several photoreceptor-specific genes.

• Ahmad W et al.
• Linkage mapping of a new syndromic form of X-linked mental retardation, MRXS7, associated with obesity.
• Eur J Hum Genet. 1999; 7: 828-32
• Display abstract

• A new syndromic form of X-linked mental retardation associated to obesity, MRXS7, has been localised to Xp11.3-Xq23 in a large Pakistani family. The ten affected males show clinical manifestations of mental retardation, obesity and hypogonadism. The family was genotyped by a set of microsatellite markers spaced at approximately 10 cM intervals on the X chromosome. Linkage to five adjacent microsatellite markers, mapping in the pericentromeric area, was established and a maximum two-point lod score of 3.86 was reached at zero recombination with marker DXS1106. Reduced recombination events around the centromere prevented precise mapping of the gene.

• Sumegi J, Gross TG, Seemayer TA
• The molecular genetics of X-linked lymphoproliferative (Duncan's) disease.
• Cancer J Sci Am. 1999; 5: 57-62

• Sossey-Alaoui K, Srivastava AK
• DCAMKL1, a brain-specific transmembrane protein on 13q12.3 that is similar to doublecortin (DCX).
• Genomics. 1999; 56: 121-6
• Display abstract

• Mutations in the human doublecortin (DCX), a brain-specific putative signaling protein, cause X-linked lissencephaly and subcortical band heterotopia. A predicted 740-amino-acid protein from human brain has two distinct regions, an N-terminal 345-amino-acid region 78% similar to the DCX protein and a C-terminal 427-amino-acid region that contains two transmembrane domains and is 98% homologous to a rat Ca2+/calmodulin-dependent protein kinase. We have designated this protein DCAMKL1. It maps to chromosome 13q12.3-q13, within a 540-kb YAC clone containing markers D13S805 and D13S1164. Northern analysis detected three major transcript isoforms of the DCAMKL1 gene expressed differentially and predominantly in human fetal and adult brain and during mouse embryogenesis (11-17 dpc). These results and its homology with the DCX and Ca2+/calmodulin dependent kinase proteins suggest a likely role for DCAMKL1 transmembrane protein in developing and adult brain, possibly in a pathway of cortical development.

• Gecz J et al.
• Characterization of the human glutamate receptor subunit 3 gene (GRIA3), a candidate for bipolar disorder and nonspecific X-linked mental retardation.
• Genomics. 1999; 62: 356-68
• Display abstract

• The X-chromosome breakpoint in a female patient with a balanced translocation t(X;12)(q24;q15), bipolar affective disorder and mental retardation was mapped within the glutamate receptor 3 (GRIA3) gene by fluorescence in situ hybridization. The GRIA3 cDNA of 5894 bp was cloned, and the gene structure and pattern of expression were determined. The most abundant GRIA3 transcript is composed of 17 exons. An additional 5 exons (2a, 2b, 5a, 5b, and 5c) from the 5' end of the GRIA3 open reading frame were identified by EST analysis (ESTs AI379066 and AA947914). Two new polymorphic microsatellite repeats, (TC)(n=12-26) and (AC)(n=15-19), were identified within GRIA3 5' and 3'UTRs. No mutations were detected in families segregating disorders mapping across GRIA3, one with X-linked bipolar affective disorder (BP) and one with a nonspecific X-linked mental retardation (MRX27). To assess the possibility of the involvement of the GRIA3 gene in familial cases of complex BP, a large set of 373 individuals from 40 pedigrees segregating BP were genotyped using closely linked (DXS1001) and intragenic (DXS1212 and GRIA3 3' UTR (AC)(n))) GRIA3 STR markers. No evidence of linkage was found by parametric Lod score analysis (the highest Lod score was 0. 3 at DXS1212, using the dominant transmission model) or by affected sib-pair analysis.

• Prakash SK, Van den Veyver IB, Franco B, Volta M, Ballabio A, Zoghbi HY
• Characterization of a novel chromo domain gene in xp22.3 with homology to Drosophila msl-3.
• Genomics. 1999; 59: 77-84
• Display abstract

• The Drosophila male-specific lethal (MSL) genes regulate transcription from the male X chromosome in a dosage compensation pathway that equalizes X-linked gene expression in males and females. The members of this gene family, including msl-1, msl-2, msl-3, mle, and mof, encode proteins with no sequence homology. However, mutations in each of these genes produce a similar phenotype: sex-specific lethality of male embryos caused by the failure of mutants to increase transcription from the single male X chromosome. The MSL gene products assemble into a multiprotein transcriptional activation complex at hundreds of sites along the chromatin of the X chromosome. Here we report the isolation and characterization of a human gene, named MSL3L1, that encodes a protein with significant homology to Drosophila MSL-3 in three distinct regions, including two putative chromo domains. MSL3L1 was identified by database queries with genomic sequence from BAC GS-590J6 (GenBank AC0004554) in Xp22.3 and was evaluated as a candidate gene for several developmental disorders mapping to this region, including OFD1 and SED tarda, as well as Aicardi syndrome and Goltz syndrome.

• Gendrot C et al.
• X-linked nonspecific mental retardation (MRX16) mapping to distal Xq28: linkage study and neuropsychological data in a large family.
• Am J Med Genet. 1999; 83: 411-8
• Display abstract

• A genetic linkage study was performed on a large four-generation family with variable nonspecific X-linked mental retardation (MRX16), speech abnormalities, and retardation of all milestones. Significant linkage was found in the Xq28 region with loci DXS52, DXS15, BGN, and DXS1108 with maximum LOD scores of 4.86, 4.01, 4.83, and 5.43, respectively, at theta = 0.00. Recombination was observed at the locus DXS1113, thus mapping the gene in an 8-Mb interval between this marker and the Xq telomere. Linkage intervals of three other MRX families overlap with this interval in Xq28 where the RABGDIA gene, mutated in the MRX41 and MRX48 families, is also located. In MRX3, MRX28, but also in MRX16, no alteration of RABGDIA has been found, thus suggesting the existence of at least two MRX genes in distal Xq28.

• Banfi S et al.
• Identification and characterization of AFG3L2, a novel paraplegin-related gene.
• Genomics. 1999; 59: 51-8
• Display abstract

• We recently identified a gene responsible for an autosomal recessive form of hereditary spastic paraplegia (HSP). This gene encodes paraplegin, a mitochondrial protein highly homologous to the yeast mitochondrial ATPases Afg3p and Rcalp, which have both proteolytic and chaperone-like activities at the inner mitochondrial membrane. By screening the Expressed Sequence Tag database, we identified and characterized a novel human cDNA, ATPase family gene 3-like 2 (AFG3L2, Human Gene Nomenclature Committee-approved symbol), which is closely related to paraplegin. This cDNA encodes a 797-amino-acid predicted protein highly similar to paraplegin as well as to yeast Afg3p and Rca1p. Immunofluorescence studies revealed that AFG3L2 and paraplegin share a similar expression pattern and the same subcellular localization, the mitochondrial compartment. We subsequently mapped AFG3L2 to chromosome 18p11 by radiation hybrid analysis. AFG3L2 may represent a candidate gene for other forms of HSPs and possibly for other neurodegenerative disorders.

• Brown AL, Kay GF
• Bex1, a gene with increased expression in parthenogenetic embryos, is a member of a novel gene family on the mouse X chromosome.
• Hum Mol Genet. 1999; 8: 611-9
• Display abstract

• Parthenogenetic and normal blastocysts were compared using differential display analysis as a means to identify new imprinted genes. A single gene was identified with increased expression in parthenogenetic blastocysts, suggesting it might be an imprinted gene expressed from the maternally inherited allele. The gene, named Bex1 (brainexpressedX-linked gene), maps near Plp on the mouse X chromosome and to Xq22 in humans. Database homology searches revealed two additional uncharacterized cDNAs similar to Bex1 that were named Bex2 and Bex3. Allele-specific expression analysis of Bex1 using F1 blastocysts indicated an excess of transcript expressed from the maternally inherited allele compared with the paternally inherited allele. This excess level of transcript derived from the maternally inherited allele may be due to imprinted X inactivation of the paternally inherited allele in the extraembryonic lineages of female embryos rather than a result of genomic imprinting.

• Gleeson JG et al.
• Characterization of mutations in the gene doublecortin in patients with double cortex syndrome.
• Ann Neurol. 1999; 45: 146-53
• Display abstract

• Mutations in the X-linked gene doublecortin, which encodes a protein with no dear structural homologues, are found in pedigrees in which affected females show "double cortex" syndrome (DC; also known as subcortical band heterotopia or laminar heterotopia) and affected males show X-linked lissencephaly. Mutations in doublecortin also cause sporadic DC in females. To determine the incidence of doublecortin mutations in DC, we investigated a cohort of eight pedigrees and 47 sporadic patients with DC for mutations in the doublecortin open reading frame as assessed by single-stranded conformational polymorphism analysis. Mutations were identified in each of the eight DC pedigrees (100%), and in 18 of the 47 sporadic DC patients (38%). Identified mutations were of two types, protein truncation mutations and single amino acid substitution mutations. However, pedigrees with DC displayed almost exclusively single amino acid substitution mutations, suggesting that patients with these mutations may have less of a reproductive disadvantage versus those patients with protein truncation mutations. Single amino acid substitution mutations were tightly clustered in two regions of the open reading frame, suggesting that these two regions are critical for the function of the Doublecortin protein.

• Tamari M, Daigo Y, Nakamura Y
• Isolation and characterization of a novel serine threonine kinase gene on chromosome 3p22-21.3.
• J Hum Genet. 1999; 44: 116-20
• Display abstract

• Through large-scale DNA sequencing of a genomic region on chromosome 3p22-p21.3, we isolated a novel gene encoding a 527-amino-acid protein. Its 18 exons spanned a genomic region of about 90 kilobases, and the 4536-nucleotide cDNA contained an open reading frame of 1581 base pairs. The gene was expressed in all 16 human tissues examined by Northern blotting. The amino acid sequence of the predicted protein was 39% identical to that of human SOK1 (Ste20/oxidant stress response kinase-1), a molecule that is activated by oxidative stress. In view of its significant similarity to SOK1, we suspect that the novel gene, which we named OSR1, is a member of the SOK family of kinases in terms of function.

• Patzak D, Zhuchenko O, Lee CC, Wehnert M
• Identification, mapping, and genomic structure of a novel X-chromosomal human gene (SMPX) encoding a small muscular protein.
• Hum Genet. 1999; 105: 506-12
• Display abstract

• Reciprocal probing has been used to identify a cDNA clone (xh8H11) representing a gene preferentially expressed in striated muscle. The gene maps close to DXS7101 31.9 cM from the short arm telomere of the X-chromosome at Xp22.1. On searching expressed and genomic databases, 21 expressed sequence tags were found that allowed the assignment of a human extended consensus sequence of 887 bp, suggesting a completely expressed gene symbolized as SMPX. By using the human consensus sequence, the orthologous mouse Smpx and rat SMPX genes could be aligned and confirmed by complete sequencing of additional SMPX-related clones obtained by library screening. An open reading frame was identified encoding a peptide of 88-86 and 85 amino acids in human and rodents, respectively. The predicted peptide had no significant homologies to known structural elements. The human consensus cDNA sequence was used to define the genomic structure of the human SMPX that had been missed by a previous large scale sequencing approach. The gene consists of five exons (> or =172, 57, 84, 148, > or =422 bp) and four introns (3639, 10410, 6052, 31134 bp) comprising together 52.1 kb and is preferentially and abundantly expressed in heart and skeletal muscle. Thus, a novel human gene encoding a small muscular protein that maps to Xp22.1 (SMPX) has been identified and structurally characterized as a basis for further functional analysis.

• Yoshimura K, Hamada F, Tomoda T, Wakiguchi H, Kurashige T
• Focal pachypolymicrogyria in three siblings.
• Pediatr Neurol. 1998; 18: 435-8
• Display abstract

• The malformation of focal pachypolymicrogyria might be the manifestation of an X-linked recessive disorder according to the results of this study. Three siblings revealed focal pachypolymicrogyria on magnetic resonance imaging (MRI) and had a strong family history of epilepsy and mental retardation. All three siblings had the same mother; the father of Patient 1 was not related to the mother, but the father of Patients 2 and 3 was related to her. The MRI of the father of Patients 2 and 3 demonstrated focal pachypolymicrogyria. The mother's MRI was normal. In this family, epilepsy or mental retardation was found mainly in the males (Patient 3 was an exception), and they were all born to female members of this family, not male. Patient 3 was probably a homozygote with an X-linked recessive inheritance, and therefore, she demonstrated the most severe clinical findings.

• Omori Y et al.
• Expression and chromosomal localization of KIAA0369, a putative kinase structurally related to Doublecortin.
• J Hum Genet. 1998; 43: 169-77
• Display abstract

• Neuropathy in vertebrates can be a consequence of failure of genes involved in the nervous system to be expressed at the correct times and levels during embryonic life. Recently, a brain specific gene, Doublecortin, was cloned and was shown to have mutations in X-linked lissencephaly and double cortex syndrome. KIAA0369 is a putative kinase that is structurally related to Doublecortin. We compared the expression of KIAA0369 with that of Doublecortin, both of which were expressed specifically or predominantly in fetal brain among 20 different tissues examined. The deduced products of both genes contain a unique domain (the Doublecortin [DC] domain), but KIAA0369 also contains a calmodulin-dependent kinase (CaM kinase)-like domain following the DC domain. We found at least four splicing variants of KIAA0369: KIAA0369-AS (type A, short version), KIAA0369-AL (type A, long version), KIAA0369-BS (type B, short version), and KIAA0369-BL (type B, long version). KIAA0369-B, which lacked the DC domain and maintained the kinase domain, was expressed in adult as well as fetal brain, but the variants that included the DC domain, KIAA0369-A, were expressed predominantly in fetal brain. These results suggest that the DC domain plays an important role in the development of the nervous system. In the adult brain, KIAA0369 was expressed in all 15 different regions examined, more intensely in cerebral cortex, occipital pole, frontal lobe, amygdala, and hippocampus, and less intensely in corpus callosum and thalamus. The murine homologs of Doublecortin and KIAA0369 were not detectable in 7-day mouse embryos, but both genes were expressed extensively in 11-day embryos. Human KIAA0369 was mapped by fluorescence in situ hybridization (FISH) to chromosome 13q13-q14.1. The presence of genes related to neuropathy has been reported in this locus.

• Monteiro de Pina-Neto J, de Molfetta GA
• The X-linked mental retardation, macrosomia, macrocephaly and obesity syndrome (Baraitser syndrome): a Brazilian case.
• Clin Dysmorphol. 1998; 7: 233-4

• Matsuo N, Kawamoto S, Matsubara K, Okubo K
• Cloning and developmental expression of the murine homolog of doublecortin.
• Biochem Biophys Res Commun. 1998; 252: 571-6
• Display abstract

• While analyzing active genes in neonatal mouse hippocampus by quantitative 3'-cDNA collection, we identified a highly conserved murine homolog of doublecortin, the causative gene of X-linked lissencephaly (XLIS) and subcortical laminar heterotopia (SCLH) syndrome. The m-doublecortin cDNA contains nearly 8 kb 3' UTR homologous to hs-doublecortin and it was mapped to the X chromosome. The expression of m-doublecortin is limited to the developing CNS, especially the cortical plate, supporting that XLIS/SCLH syndrome is associated with an arrest of neuronal migration in the cerebral cortex. The m-doublecortin mRNA was absent in the ventricular zone where neuronal precursors proliferate, and interestingly it was found in various brain structures that are not typically affected in patients with this syndrome.

• Fernandez MP, Copeland NG, Gilbert DJ, Jenkins NA, Morgan RO
• Mouse annexin III cDNA, genetic mapping and evolution.
• Gene. 1998; 207: 43-51
• Display abstract

• Mouse annexin III cDNA was characterized from I.M.A.G.E. Consortium (LLNL) expressed sequence tag clones by molecular sequencing, chromosomal mapping and systematic analysis. cDNA sequences extended the known 5' and 3' untranslated regions and confirmed the location of intron 7 with respect to the human gene. The Anx3 locus mapped to the middle of mouse chromosome 5 between Areg and Fgf5. Protein-coding regions were compared with homologous annexins to establish subfamily identity, structural conservation and divergence pattern. Annexin III exhibited low functional constraint against structural change and weak phylogenetic association with known annexins. The rapid, constant divergence of human and rodent annexins III from each other and from other annexin subfamilies was used to estimate gene separation times. Phylogenetic, phenetic and structural data suggested a possible direct or indirect separation of annexin III from XI approximately 317 million years ago.

• Lakaye B, Minet A, Zorzi W, Grisar T
• Cloning of the rat brain cDNA encoding for the SLC-1 G protein-coupled receptor reveals the presence of an intron in the gene.
• Biochim Biophys Acta. 1998; 1401: 216-20
• Display abstract

• In order to isolate new G protein-coupled receptors expressed in the cerebral cortex, a set of degenerate oligonucleotides corresponding to the third and seventh transmembrane segment were synthetized. Their use in PCR on rat brain cortex mRNA amplified several cDNA fragments. One of them, a 526 bp sequence, encoded for what was at that time an unknown G protein-coupled receptor. An oligonucleotide derived from the sequence was then used as a probe to isolate the receptor cDNA from a rat brain cDNA library. It encodes for a 353aa protein with seven transmembrane segments, three consensus N-glycosylation sites at the amino terminus and several potential phosphorylation sites in the intracellular loops. This protein shares 91% overall identity with a recently cloned human somatostatin-like receptor of 402aa named SLC-1. This suggests that we have cloned the rat orthologue of the human SLC-1. However, the extracellular N-terminus of the human receptor is 49 amino acids longer and shows 50% identity with the rat one. Because the human sequence was deduced from genomic DNA, we suspected the presence of an intron in the gene. This was confirmed by PCR using primers spanning the intron. On the basis of the sequence of a 128 kb fragment of chromosome 22 encompassing the SLC-1 gene, we were able to deduce a corrected amino acids sequence for the human receptor. So both rat and human SLC-1 receptors are 353aa long, with three consensus N-glycosylation sites. They share 96% identity at the amino acid level and are encoded by a gene containing one intron in the coding sequence.

• Puche A, Rodriguez T, Domingo R, Casas C, Vicente T, Martinez-Lage JF
• X-linked subcortical laminar heterotopia and lissencephaly: a new family.
• Neuropediatrics. 1998; 29: 276-8
• Display abstract

• Magnetic resonance imaging (MRI) has enabled the identification of neuronal migration disorders in living subjects. This represents an important achievement in the diagnosis of patients with these anomalies. At least five affected families with coexistent subcortical laminar heterotopia and lissencephaly have been reported recently. This association suggests an X-linked pattern of inheritance. In the family that we report, the mother suffered from epilepsy and the oldest daughter from epilepsy and mental retardation. Both patients showed subcortical laminar heterotopia on MRI. The youngest son presented a severe encephalopathy with early onset seizures, and was found to show lissencephaly on MRI. The other two siblings, a boy and a girl, had no neurological abnormalities. The severity of these patients' clinical symptoms were clearly related to MRI findings.

• Toyama J, Kasuya H, Higuchi S, Kondo H, Naganuma Y, Uchiyama M
• Familial neuronal migration disorder: subcortical laminar heterotopia in a mother and pachygyria in the son.
• Am J Med Genet. 1998; 75: 481-4
• Display abstract

• We describe clinical manifestations and magnetic resonance imaging (MRI) findings in a man and his mother who were diagnosed as having a neuronal migration disorder. The son had severe psychomotor retardation and the mother had intractable seizures and mild psychomotor retardation. MRI demonstrated moderate pachygyria in the son and subcortical heterotopia in the mother. In both patients, the frontal parts of the brain were characteristically more affected than any other areas. A dominant pattern of inheritance in the family suggests a genetic role in the underlying cause of the migration disorder. The difference in severity between the two patients also suggests an X-linked dominant inheritance. Our family fits the condition of X-linked lissencephaly.

• Chelly J
• Doublecortin: the latest breakthrough in neuronal migration and cortical development.
• Mol Psychiatry. 1998; 3: 290-2

• Schultz DC, Balasara BR, Testa JR, Godwin AK
• Cloning and localization of a human diphthamide biosynthesis-like protein-2 gene, DPH2L2.
• Genomics. 1998; 52: 186-91
• Display abstract

• Sequence analysis of the candidate tumor suppressor OVCA1 revealed extensive sequence identity and similarity to proteins from a diverse number of species, including the yeast diphthamide biosynthesis protein-2, dph2, which suggested that OVCA1 may be the human homologue to this yeast gene. However, searches of the translated EST database for sequences in common with dph2 and OVCA1 uncovered an EST, h52976, with significant amino acid conservation with dph2. Isolation of a cDNA clone encompassing the EST by RACE methodologies and sequence analysis indicate the identification of a previously unidentified gene that is ubiquitously expressed and maps to chromosome 1p34. Based on amino acid sequence analysis, the 489-amino-acid protein encoded by this novel gene is distinct from OVCA1 and is more closely related to the yeast dph2 gene product. Therefore, we refer to this novel gene as DPH2L2, which constitutes one member of a novel gene family that may be involved in diphthamide biosynthesis in humans.

• Berg MJ et al.
• X-linked female band heterotopia-male lissencephaly syndrome.
• Neurology. 1998; 50: 1143-6
• Display abstract

• We report a family with band heterotopia in a mother and daughter and lissencephaly in a son (X-linked inheritance pattern). Postmortem examination of the boy revealed classical lissencephaly and, among other findings, simplified and discontinuous inferior olives without inferior olivary heterotopia. The absence of inferior olivary heterotopia may distinguish X-linked lissencephaly from other conditions with classic lissencephaly such as Miller-Dieker syndrome.

• Hayes MW, Ouvrier RA, Evans W, Somerville E, Morris JG
• X-linked Dystonia-Deafness syndrome.
• Mov Disord. 1998; 13: 303-8
• Display abstract

• We report a family with early-onset deafness and progressive dystonia exclusively involving males over two successive generations. There is also evidence of cognitive impairment and corticospinal tract involvement. The pedigree suggests an X-linked inheritance. A similar family was originally described by Scribanu and Kennedy. Tranebjaerg et al. have recently reported two other families with linkage to Xq22 and also proposed a novel X-linked candidate gene. These findings support the existence of a distinct neurodegenerative syndrome principally characterized by early-onset deafness and progressive dystonia. Neuropathology of one case showed a mosaic pattern of neuronal loss and gliosis in the caudate and putamen suggesting that this pattern is not restricted to XDP or Lubag.

• Nilden F, Backstrom A, Bark C
• Molecular cloning and characterisation of a mouse gene encoding an isoform of the neuronal cyclin-dependent kinase 5 (CDK5) activator.
• Biochim Biophys Acta. 1998; 1398: 371-6
• Display abstract

• We have isolated and characterised the mouse gene for the p39 activator, designated p39is, which encodes a protein of 369 amino acids. The mouse p39 protein exhibits 95% amino acid identity to a previously characterised human p39 cDNA and the novel gene sequence corresponds to a single genomic locus in mouse. The p39is mRNA is highly expressed in the mouse central nervous system.

• Warneke-Wittstock R, Marquardt A, Gehrig A, Sauer CG, Gessler M, Weber BH
• Transcript map of a 900-kb genomic region in Xp22.1-p22.2: identification of 12 novel genes.
• Genomics. 1998; 51: 59-67
• Display abstract

• The Xp22.1-p22.2 interval is a focus of interest as a number of hereditary disease loci have been mapped to this region, including X-linked nonsyndromic sensorineural deafness (DFN6), X-linked juvenile retinoschisis (RS), and several X-linked mental retardation syndromes. In the course of cloning the RS gene we have assembled YAC and PAC contigs of the 900-kb candidate region delimited by DXS418 and DXS999. In this study, we now report the construction of a first transcript map of this chromosomal interval by combining exon trapping, EST mapping, and computational gene identification methods. Overall, this strategy has led to the assembly of at least 12 novel transcripts positioned within the DXS418-DXS999 region, one of these encoding a putative protein kinase motif with significant homology to the rat p58/GTA protein kinase domain and another a putative neuronal protein with strong homology to a Drosophila transcriptional repressor.

• Yntema HG et al.
• Localisation of a gene for non-specific X linked mental retardation (MRX46) to Xq25-q26.
• J Med Genet. 1998; 35: 801-5
• Display abstract

• We report linkage data on a new large family with non-specific X linked mental retardation (MRX), using 24 polymorphic markers covering the entire X chromosome. We could assign the underlying disease gene, denoted MRX46, to the Xq25-q26 region. MRX46 is tightly linked to the markers DXS8072, HPRT, and DXS294 with a maximum lod score of 5.12 at theta=0. Recombination events were observed with DXS425 in Xq25 and DXS984 at the Xq26-Xq27 boundary, which localises MRX46 to a 20.9 cM (12 Mb) interval. Several X linked mental retardation syndromes have been mapped to the same region of the X chromosome. In addition, the localisation of two MRX genes, MRX27 and MRX35, partially overlaps with the linkage interval obtained for MRX46. Although an extension of the linkage analysis for MRX35 showed only a minimal overlap with MRX46, it cannot be excluded that the same gene is involved in several of these MRX disorders. On the other hand, given the considerable genetic heterogeneity in MRX, one should be extremely cautious in using interfamilial linkage data to narrow down the localisation of MRX genes. Therefore, unless the underlying gene(s) is characterised by the analysis of candidate genes, MRX46 can be considered a new independent MRX locus.

• Pilz DT et al.
• LIS1 and XLIS (DCX) mutations cause most classical lissencephaly, but different patterns of malformation.
• Hum Mol Genet. 1998; 7: 2029-37
• Display abstract

• Classical lissencephaly (LIS) is a neuronal migration disorder resulting in brain malformation, epilepsy and mental retardation. Deletions or mutations of LIS1 on 17p13.3 and mutations in XLIS ( DCX ) on Xq22.3-q23 produce LIS. Direct DNA sequencing of LIS1 and XLIS was performed in 25 children with sporadic LIS and no deletion of LIS1 by fluorescence in situ hybridization. Mutations of LIS1 were found by sequencing ( n = 8) and Southern blot ( n = 2) in a total of 10 patients (40%) of both sexes and mutations of XLIS in five males (20%). Combined with previous data, deletions or mutations of these two genes account for approximately 76% of isolated LIS. These data demonstrate that LIS1 and XLIS mutations cause the majority of, though not all, human LIS. The mutations in LIS1 were predicted to result in protein truncation in six of eight patients and splice site mutations in two, all of which disrupt one or more of the seven WD40 repeats contained in the LIS1 protein. Point mutations in XLIS identified the C-terminal serine/proline-rich region as potentially important for protein function. The patients with mutations were included in a genotype-phenotype analysis of 32 subjects with deletions or other mutations of these two genes. Whereas the brain malformation due to LIS1 mutations was more severe over the parietal and occipital regions, XLIS mutations produced the reverse gradient, which was more severe over the frontal cortex. The distinct LIS patterns suggest that LIS1 and XLIS may be part of overlapping, but distinct, signaling pathways that promote neuronal migration.

• Page DC
• Save the males!
• Nat Genet. 1997; 17: 3-3

• Musumeci SA et al.
• A new family with periventricular nodular heterotopia and peculiar dysmorphic features. A probable X-linked dominant trait.
• Arch Neurol. 1997; 54: 61-4
• Display abstract

• OBJECTIVE: To describe 3 sisters with brain periventricular heterotopia and peculiar dysmorphic features as a probable X-linked dominant trait. DESIGN: Clinical, laboratory, neurophysiological, and brain imaging data were studied. SETTING: Research institute for mental retardation. PATIENTS: The 3 sisters had mental retardation, drug-resistant epilepsy, gray matter heterotopia, and peculiar malformations (low nasal bridge, upslanting palpebral fissures, palpebral edema, attached hypoplastic earlobes, thickened calvaria, rectal fibrovascular polyps, urinary tract anomalies, and increased foot length). The patients were 35, 30, and 25 years old and belonged to a sibship of 6, born of nonconsanguineous healthy parents. CONCLUSION: The 3 patients constitute a well-defined clinical entity not previously described of a probable X-linked dominant nature.

• Ryan SG, Chance PF, Zou CH, Spinner NB, Golden JA, Smietana S
• Epilepsy and mental retardation limited to females: an X-linked dominant disorder with male sparing.
• Nat Genet. 1997; 17: 92-5
• Display abstract

• Several X-linked disorders affect females disproportionately or exclusively. These including focal dermal hypoplasia, oral-facial-digital syndrome type I (ref. 3) and epilepsy with bilateral periventricular heterotopias. X-linked dominant inheritance with male lethality is probably responsible for sex-limited expression of these disorders, as affected women have frequent spontaneous abortions and the sex ratio of their live offspring is often skewed. The same inheritance pattern has been proposed for Rett syndrome, Aicardi syndrome and microphthalmia with linear skin defects, but in these sporadic conditions, evidence of male lethality is lacking. We investigated an unusual family with epilepsy and mental retardation limited to females (EFMR, #121250 in ref. 9); this disorder is transmitted both by females and by completely unaffected carrier males. Assignment of the EFMR disease locus (EFMR) to the X chromosome indicates that selective involvement of females in X-linked disease may in some instances result from male sparing rather than male lethality.

• des Portes V et al.
• Dominant X linked subcortical laminar heterotopia and lissencephaly syndrome (XSCLH/LIS): evidence for the occurrence of mutation in males and mapping of a potential locus in Xq22.
• J Med Genet. 1997; 34: 177-83
• Display abstract

• X linked subcortical laminar heterotopia and lissencephaly syndrome (XSCLH/ LIS) is an intriguing disorder of cortical development, which causes classical lissencephaly with severe mental retardation and epilepsy in hemizygous males, and subcortical laminar heterotopia (SCLH) associated with milder mental retardation and epilepsy in heterozygous females. Here we report an exclusion mapping study carried out in three unrelated previously described families in which males are affected with lissencephaly and females with SCLH, using 38 microsatellite markers evenly distributed on the X chromosome. Most of the X chromosome was excluded and potential intervals of assignment in Xq22.3-q23 or in Xq27 are reported. Although the number of informative meioses did not allow a decision between these two loci, it is worth noting that the former interval is compatible with the mapping of a breakpoint involved in a de novo X;autosomal balanced translocation 46,XX,t(X;2)(q22;p25) previously described in a female with classical lissencephaly. In addition, haplotype inheritance in two families showed a grandpaternal origin of the mutation and suggested in one family the presence of mosaicism in germline cells of normal transmitting males.

• Fink JM, Dobyns WB, Guerrini R, Hirsch BA
• Identification of a duplication of Xq28 associated with bilateral periventricular nodular heterotopia.
• Am J Hum Genet. 1997; 61: 379-87
• Display abstract

• Bilateral periventricular nodular heterotopia (BPNH) is a malformation of neuronal migration and is characterized by nodules of heterotopic gray matter lining the lateral ventricles of the brain. The majority of BPNH patients are female and have epilepsy as a sole clinical manifestation of their disease. Familial BPNH has been mapped to Xq28 by linkage analysis. A multiple congenital anomaly-mental retardation syndrome (BPNH/MR) was recently delineated in three unrelated boys with BPNH, cerebellar hypoplasia, severe mental retardation, epilepsy, and syndactyly. High-resolution chromosome analysis revealed a subtle abnormality of Xq28 in one of the boys with BPNH/MR syndrome. FISH with cosmids and YACs from Xq28 further characterized this abnormality as a 2.25-3.25-Mb inverted duplication. No abnormality of Xq28 was detected by G-banding or FISH in the other two boys. These data support the linkage assignment of BPNH to band Xq28 and narrow the critical region to the distal 2.25-3.25 Mb of Xq28.

• Shastry BS, Hejtmancik JF, Trese MT
• Identification of novel missense mutations in the Norrie disease gene associated with one X-linked and four sporadic cases of familial exudative vitreoretinopathy.
• Hum Mutat. 1997; 9: 396-401
• Display abstract

• X-linked Familial Exudative Vitreoretinopathy (XLFEVR) is a hereditary eye disorder that affects both the retina and the vitreous body. It is characterized by an abnormal vascularization of the peripheral retina. It has been previously shown by linkage and candidate gene analysis that XLFEVR and Norrie disease are allelic. In this report we describe four novel mutations (R41K, H42R, K58N, and Y120C) in the Norrie disease gene associated with one X-linked and four sporadic cases of FEVR. One mutation (H42R) was found to be segregating with the disease in three generations (X-linked family), and the others are sporadic. These sequence alterations changed the encoded amino acids in the Norrie disease protein and were not found in 17 unaffected family members or in 36 randomly selected normal individuals. This study provides additional evidence that mutations in the same gene can result in FEVR and Norrie disease. It also demonstrates that it may be beneficial for clinical diagnosis to screen for mutations in the Norrie disease gene in sporadic FEVR cases.

• Ross ME et al.
• Linkage and physical mapping of X-linked lissencephaly/SBH (XLIS): a gene causing neuronal migration defects in human brain.
• Hum Mol Genet. 1997; 6: 555-62
• Display abstract

• While disorders of neuronal migration are associated with as much as 25% of recurrent childhood seizures, few of the genes required to establish neuronal position in cerebral cortex are known. Subcortical band heterotopia (SBH) and lissencephaly (LIS), two distinct neuronal migration disorders producing epilepsy and variable cognitive impairment, can be inherited alone or together in a single pedigree. Here we report a new genetic locus, XLIS, mapped by linkage analysis of five families and physical mapping of a balanced X;2 translocation in a girl with LIS. Linkage places the critical region in Xq21-q24, containing the breakpoint that maps to Xq22.3-q23 by high-resolution chromosome analysis. Markers used for somatic cell hybrid and fluorescence in situ hybridization analyses place the XLIS region within a 1 cM interval. These data suggest that SBH and X-linked lissencephaly are caused by mutation of a single gene, XLIS, that the milder SBH phenotype in females results from random X-inactivation (Lyonization), and that cloning of genes from the breakpoint region on X will yield XLIS.

• Trivier E et al.
• Mutations in the kinase Rsk-2 associated with Coffin-Lowry syndrome.
• Nature. 1996; 384: 567-70
• Display abstract

• The Coffin-Lowry syndrome (CLS), an X-linked disorder, is characterized by severe psychomotor retardation, facial and digital dysmorphisms, and progressive skeletal deformations. Genetic linkage analysis mapped the CLS locus to an interval of 2-3 megabases at Xp22.2. The gene coding for Rsk-2, a member of the growth-factor-regulated protein kinases, maps within the candidate interval, and was tested as a candidate gene for CLS. Initial screening for mutations in the gene for Rsk-2 in 76 unrelated CLS patients revealed one intragenic deletion, a nonsense, two splice site, and two missense mutations. The two missenses affect sites critical for the function of Rsk-2. The mutated Rsk-2 proteins were found to be inactive in a S6 kinase assay. These findings provide direct evidence that abnormalities in the MAPK/RSK signalling pathway cause Coffin-Lowry syndrome.

• Dobyns WB et al.
• X-linked malformations of neuronal migration.
• Neurology. 1996; 47: 331-9
• Display abstract

• Malformations of neuronal migration such as lissencephaly (agyria-pachygyria spectrum) are well-known causes of mental retardation and epilepsy that are often genetic. For example, isolated lissencephaly sequence and Miller-Dieker syndrome are caused by deletions involving a lissencephaly gene in chromosome 17p13.3, while many other malformation syndromes have autosomal recessive inheritance. In this paper, we review evidence supporting the existence of two distinct X-linked malformations of neuronal migration. X-linked lissencephaly and subcortical band heterotopia (XLIS) presents with sporadic or familial mental retardation and epilepsy. The brain malformation varies from classical lissencephaly, which is observed in males, to subcortical band heterotopia, which is observed primarily in females. The XLIS gene is located in chromosome Xq22.3 based on the breakpoint of an X-autosomal translocation. Bilateral periventricular nodular heterotopia (BPNH) usually presents with sporadic or familial epilepsy with normal intelligence, primarily in females, although we have evaluated two boys with BPNH and severe mental retardation. The gene for BPNH has been mapped to chromosome Xq28 based on linkage studies in multiplex families and observation of a subtle structural abnormality in one of the boys with BPNH and severe mental retardation.

• Jin H et al.
• A novel X-linked gene, DDP, shows mutations in families with deafness (DFN-1), dystonia, mental deficiency and blindness.
• Nat Genet. 1996; 14: 177-80
• Display abstract

• In 1960, progressive sensorineural deafness (McKusick 304,700, DFN-1) was shown to be X-linked based on a description of a large Norwegian pedigree. More recently, it was shown that this original DFN-1 family represented a new type of recessive neurodegenerative syndrome characterized by postlingual progressive sensorineural deafness as the first presenting symptom in early childhood, followed by progressive dystonia, spasticity, dysphagia, mental deterioration, paranoia and cortical blindness. This new disorder, termed Mohr-Tranebjaerg syndrome (referred to here as DFN-1/MTS) was mapped to the Xq21.3-Xq22 region2. Using positional information from a patient with a 21-kb deletion in chromosome Xq22 and sensorineural deafness along with dystonia, we characterized a novel transcript lying within the deletion as a candidate for this complex syndrome. We now report small deletions in this candidate gene in the original DFN-1/MTS family, and in a family with deafness, dystonia and mental deficiency but not blindness. This gene, named DDP (deafness/ dystonia peptide), shows high levels of expression in fetal and adult brain. The DDP protein demonstrates striking similarity to a predicted Schizosaccharomyces pombe protein of no known function. Thus, is it likely that the DDP gene encodes an evolutionarily conserved novel polypeptide necessary for normal human neurological development.

• Izumoto S et al.
• A new mutation of the L1CAM gene in an X-linked hydrocephalus family.
• Childs Nerv Syst. 1996; 12: 742-7
• Display abstract

• X-linked hydrocephalus is a genetic form of hydrocephalus that frequently occurs in females. It is characterized by ventricular dilatation, mental retardation, deformity of the thumb and spastic paraparesis. Recently, 23 different mutations of the gene for the neural cell adhesion molecule, L1CAM, located at chromosome region Xq28, have been reported, 16 of which were detected in families with X-linked hydrocephalus. We sequenced the coding region of the L1CAM gene of patients from two different families with X-linked hydrocephalus and found a novel mutation at nucleotide residue 1963 in one family. This mutation from adenine to guanine results in an amino acid change from lysine to glutamic acid at residue 655 of the L1CAM protein, which belongs to the fibronectin type III domain. We report another method of the rapid identification of the mutation based on the polymerase chain reaction. This mutation was not detected among 70 X chromosomes from a healthy population. Ours is the first report demonstrating this gene mutation in X-linked hydrocephalus in an Asian population. Our findings further emphasize the evolving genotypic heterogeneity in X-linked hydrocephalus.

• Pinard JM, Motte J, Chiron C, Brian R, Andermann E, Dulac O
• Subcortical laminar heterotopia and lissencephaly in two families: a single X linked dominant gene.
• J Neurol Neurosurg Psychiatry. 1994; 57: 914-20
• Display abstract

• Neuronal migration disorders can now be recognised by MRI. This paper reports two families in which the mothers had subcortical laminar heterotopia and four of their children had either similar heterotopia (two girls) or severe pachygyria or lissencephaly (two boys). Laminar heterotopia was more evident on MRI T2 weighted images. The patients had mild to severe epilepsy and mental retardation depending on the extent of cortical abnormalities. In these families, subcortical laminar heterotopia, pachygyria, and lissencephaly seem to share the same X linked or autosomal dominant gene. No chromosomal abnormalities, especially of chromosome 17, could be identified. For appropriate genetic counselling of the family of a child with lissencephaly or subcortical laminar heterotopia, MRI should be performed in parents or siblings with mental retardation or epilepsy.

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