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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

X-linked forms of mental retardation (MR) affect approximately 1 in 600 males and are likely to be highly heterogeneous. They can be categorized into syndromic (MRXS) and nonspecific (MRX) forms. In MRX forms, affected patients have no distinctive clinical or biochemical features. At least five MRX genes have been identified by positional cloning, but each accounts for only 0.5%-1.0% of MRX cases. Here we show that the gene TM4SF2 at Xp11.4 is inactivated by the X breakpoint of an X;2 balanced translocation in a patient with MR. Further investigation led to identification of TM4SF2 mutations in 2 of 33 other MRX families. RNA in situ hybridization showed that TM4SF2 is highly expressed in the central nervous system, including the cerebral cortex and hippocampus. TM4SF2 encodes a member of the tetraspanin family of proteins, which are known to contribute in molecular complexes including beta-1 integrins. We speculate that through this interaction, TM4SF2 might have a role in the control of neurite outgrowth.
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PMID:A new gene involved in X-linked mental retardation identified by analysis of an X;2 balanced translocation. 1065 63

X-linked forms of mental retardation (XLMR) include a variety of different disorders and may account for up to 25% of all inherited cases of mental retardation. So far, seven X-chromosomal genes mutated in nonspecific mental retardation (MRX) have been identified: FMR2, GDI1, RPS6KA3, IL1RAPL, TM4SF2, OPHN1 and PAK3 (refs 2-9). The products of the latter two have been implicated in regulation of neural plasticity by controlling the activity of small GTPases of the Rho family. Here we report the identification of a new MRX gene, ARHGEF6 (also known as alphaPIX or Cool-2), encoding a protein with homology to guanine nucleotide exchange factors for Rho GTPases (Rho GEF). Molecular analysis of a reciprocal X/21 translocation in a male with mental retardation showed that this gene in Xq26 was disrupted by the rearrangement. Mutation screening of 119 patients with nonspecific mental retardation revealed a mutation in the first intron of ARHGEF6 (IVS1-11T-->C) in all affected males in a large Dutch family. The mutation resulted in preferential skipping of exon 2, predicting a protein lacking 28 amino acids. ARHGEF6 is the eighth MRX gene identified so far and the third such gene to encode a protein that interacts with Rho GTPases.
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PMID:Mutations in ARHGEF6, encoding a guanine nucleotide exchange factor for Rho GTPases, in patients with X-linked mental retardation. 1101 88

Mental retardation (MR) is a group of heterogeneous clinical conditions. There are more than 900 genetic disorders associated with MR and it affects around 3% of the general population. MR can be subdivided into syndromic, if it is characterized by consistent and distinctive clinical findings, and nonspecific, if mental retardation is the only primary symptom among affected individuals. Many MR conditions described are syndromic, fragile X syndrome being the most common clinical entity among them. In the past years, knowledge of the molecular basis of mental retardation has increased remarkably. Eight genes involved in nonspecific X-linked MR have been identified so far, including FMR2, OPHN1, GDI1, PAK3, IL1RAPL, TM4SF2, VCX-A, and ARHGEF6. Two other genes also located on the X chromosome have been involved both in syndromic and in MRX forms (RSK2 and XNP/ATR-X). New insights into the pathogenesis of mental retardation are being provided by the discovery of these genes involved in different cellular signaling pathways in the central nervous system although many others remain to be identified.
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PMID:Genes responsible for nonspecific mental retardation. 1116 35

X-linked forms of non-specific mental retardation are complex disorders, for which mutations in several genes have recently been identified. These include OPHN1, GDI1, PAK3, IL1RAPL, TM4SF2, FMR2 and RSK2. To investigate the mechanisms through which alterations of these gene products could result in cognitive impairment, we analyzed their expression using quantitative PCR technique in two in vitro models of activity-dependent gene regulation: kainate-induced seizures and long-term synaptic potentiation (LTP). We found that the level of expression of four genes, PAK3, IL1RAPL, RSK2 and TM4SF2, was significantly up-regulated following kainate treatment. Furthermore we observed a significant increase in mRNA levels of PAK3 and IL1RAPL following LTP induction. These results suggest a possible role for these four genes in activity-dependent brain plasticity.
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PMID:Activity-dependent regulation of genes implicated in X-linked non-specific mental retardation. 1220 50

Nonspecific X-linked mental retardation (MRX) patients are characterized by mental retardation, without additional distinguishing features. Consequently, MRX families can only be distinguished by mapping studies; yet, due to imprecise mapping studies performed in the past, the number of genes causing MRX is debatable, and a more precise localization for families is necessary to estimate this number. MRX 9 has been mapped to the pericentromeric region Xp21-q13. We refined the mapping of the MRX9 family to Xp11.22-Xp11.4. A sequencing analysis of three likely candidate genes in Xp11, SREB3, synapsin I, and TM4SF2, revealed no mutations.
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PMID:Family MRX9 revisited: further evidence for locus heterogeneity in MRX. 1223 14

The TM4SF2 gene (localized at Xp11.4 between the loci DXS564 and DXS556) has been found to be mutated in one MRX family. In order to define the corresponding behavioral phenotype, global IQ and specific cognitive skills were assessed in seven males and three females of this family, independent of subject status. Mental retardation (MR) was mild in three patients and moderate in three others. Despite the broad variability of severity of MR, a cognitive profile specific to the MR in this family was documented. It was characterized by language disorder that was more marked in the articulatory component and spatial/verbal short-term memory dissociation with larger mnemonic span for spatial than for verbal cues. Linkage analysis was then performed on the basis of the cognitively determined status. Recombinations were observed with the loci DXS556 at Xp11.4 and DXS441 at Xq13.2 (maximum LOD score = 2.23 at theta = 0 for ALAS2). This localization region does not include the TM4SF2 gene that has been found mutated in both patients with MR and in one non-MR male subject of this family. The present results suggest two main hypotheses. First, TM4SF2 gene mutation could be involved in MR in this family, therefore representing accentuated intra familial phenotypic variability. Second, the structural particularity detected in the TM4SF2 gene might reflect a rare polymorphism rather than a pathogenic mutation, with the gene responsible for MR in this family being therefore more likely to be searched for in the pericentromeric region of the X chromosome.
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PMID:TM4SF2 gene involvement reconsidered in an XLMR family after neuropsychological assessment. 1237 45

Mental retardation (MR) is a symptom in a large group of clinical conditions and affects around 3% of the population. MR is divided into syndromic, if it is characterized by distinctive clinical features and nonspecific when mental retardation is the only defining manifestation. Although genetic causes of X-linked mental retardation (XLMR) are heterogenous and complex, recent findings have led to the identification of an increasing number of genes involved in these conditions. Eight genes involved in nonspecific X-linked mental retardation have been identified so far, including FMR2, GDI1, OPHN1, PAK3, ARHGEF6, IL1RAPL, TM4SF2, and FACL4. Four other MECP2, RSK2, ARX, ATR-X are involved in syndromic and nonspecific forms of MR. Recent research has shown that these genes encode for proteins involved in signaling pathways which regulate cytoskeleton organization, synaptic vesicle transport and establishment of connections between neuronal cells. These findings provide insight into the molecular mechanisms of crucial processes for the development of intellectual and cognitive functions.
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PMID:[Monogenic causes of nonspecific X-linked mental retardation molecular aspects]. 1281 Sep 81

In an ongoing study human X chromosomal mental retardation genes (MRX) were mapped in the chicken genome. Up to now the homologs of 13 genes were localized by FISH techniques. Four genes from HSAXp (TM4SF2, RSK2/RPS6KA3, NLGN4, ARX) map to GGA1q13-->q31, and seven genes from HSAXq (OPHN1, AGTR2, ARHGEF6, PAK3, FACL4/ACS4, FMR2, ATRX) to GGA4p. The gene-rich region of HSAXq28 proved to be much less conserved. GDI1 localized to GGA1pter and SLC6A8 to a mid-sized microchromosome. The order of the genes was determined from the newly available genome sequence data from chicken, which reveals exact colinearity between the genes in HSAXp and GGA1q13-->q31, but completely scrambled gene order between the genes with common synteny from HSAXq and GGA4p. This result supports the hypothesis that the human X chromosome is a real ancient autosomal linkage group.
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PMID:Localization of human X chromosomal mental retardation (MRX) genes in chicken and comparison with the chicken genome sequence data. 1562 55

Mental retardation is more common in males than females in the population, assumed to be due to mutations on the X chromosome. The prevalence of the 24 genes identified to date is low and less common than expansions in FMR1, which cause Fragile X syndrome. Systematic screening of all other X linked genes in X linked families with mental retardation is currently not feasible in a clinical setting. The phenotypes of genes causing syndromic and non-syndromic mental retardation (NLGN3, NLGN4, RPS6KA3(RSK2), OPHN1, ATRX, SLC6A8, ARX, SYN1, AGTR2, MECP2, PQBP1, SMCX, and SLC16A2) are first discussed, as these may be the focus of more targeted mutation analysis. Secondly, the relative prevalence of genes causing only non-syndromic mental retardation (IL1RAPL1, TM4SF2, ZNF41, FTSJ1, DLG3, FACL4, PAK3, ARHGEF6, FMR2, and GDI) is summarised. Thirdly, the problem of recurrence risk where a molecular genetics diagnosis has not been made and what proportion of the male excess of mental retardation is due to monogenic disorders of the X chromosome are discussed.
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PMID:X linked mental retardation: a clinical guide. 1611 46

Duplications of the short arm of the X chromosome in male patients are rare. We report on the clinical features of mentally retarded patients in two families with different interstitial duplications of Xp and their characterization by tiling path array comparative genomic hybridization (array CGH). In Family A, we detected a duplication of 9.3 Mb in Xp11p21 in a male with severe mental retardation [karyotype 46,XY,dup(X)(p11.3p21.1)] and his healthy mother. The clinical features of this patient--severe mental retardation, obesity, macrocephaly--are in accordance with those of a previously reported patient with a similar duplication. In Family B, a duplication of 8.5 Mb was diagnosed in Xp22 in three male patients with mental retardation [karyotype 46,XY,dup(X)(p22.11p22.2)] and two healthy females. Characterization of the duplications by array CGH enabled the identification of the genes within these intervals. These comprise known mental retardation genes such as MAOA, NDP, TM4SF2, NDP, RSK2, and CDKL5. Duplication of MAOA will be discussed as a possible cause of obesity.
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PMID:Characterization of interstitial Xp duplications in two families by tiling path array CGH. 1807 17


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