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

We describe a family with two male members showing an X/Y translocation (karyotype: 46,Y,der(X)t(X;Y)(p22;q11]. At physical examination both patients showed ichthyosis, mental retardation and dysmorphic features. Chondrodysplasia punctata and short stature were present in one case. Direct DNA analysis, using a steroid sulphatase cDNA probe, was performed in one patient, his mother and sister, both carriers of the translocation. We found that the translocated region of the Y chromosome includes the steroid sulphatase pseudogene. These results suggest that in our patients the X/Y translocation may be derived from a recombinational event between homologous regions located on the short arm of the X chromosome and the long arm of the Y chromosome. Clinical and molecular studies on the present family add further information for the construction of a tentative physical map of the distal Xp.
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PMID:X/Y translocation in a family with X-linked ichthyosis, chondrodysplasia punctata, and mental retardation: DNA analysis reveals deletion of the steroid sulphatase gene and translocation of its Y pseudogene. 316 28

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder. To date, a relatively small number of NF1 mutations have been characterized, thus precluding genotype-phenotype correlations. By genotyping 75 NF1 families, we have detected six hemizygous patients (two of whom are members of the same family). The five presumed deletions were confirmed by two quantitative methods of analysis of NF1 copy number: Southern hybridization with cDNA probes and a single-strand conformation polymorphism analysis that discriminates between the NF1 gene and the pseudogene sequences. The five deletions remove most of the NF1 gene, at least 225 kb, from exon 9 to the 3' end of the coding sequence. The origin of de novo mutations in the NF1 gene has been reported to be mainly paternal but we have determined that four of the de novo deletions involved the maternal chromosome and one the paternal chromosome. The six patients with deletions exhibited precocious, multiple clinical features of the disease. The incidence of tumor complications, particularly plexiform neurofibromas and intracranial tumors, among this group of patients is higher than the observed incidence in our NF1 population, suggesting that NF1 haploinsufficiency may cause a more severe phenotype with regard to tumor development. In contrast to other reports that associated large deletions with mildly dysmorphic facies, mental retardation and a large number of cutaneous neurofibromas, only one out of our six patients presented this phenotype.
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PMID:Identification of de novo deletions at the NF1 gene: no preferential paternal origin and phenotypic analysis of patients. 918 63

The human Xq11-Xq21.3 region has been implicated in several inherited disorders including dystonia-parkinsonism (DYT3), sideroblastic anemia and several specific and non-specific forms of mental retardation (MR) syndromes. As part of a positional cloning effort to identify MR genes, we have generated a YAC-based transcript map. We first constructed a YAC/STS framework by extending previously published contigs. This framework map consists of a minimal set of 119 clones, covering approximately 20 Megabases (Mb) and allowing the precise ordering of 71 STSs between DXS136 and DXS472. This YAC contig was then used to define the positions of genes and expressed sequence tags (ESTs) assigned to the Xcen-Xq21.3 region. In addition to the genes previously localized to this part of the X chromosome, 18 transcription units corresponding to additional known genes or gene family members, one pseudogene and 15 novel transcripts were mapped. This transcriptional map incorporates 51 transcription units and provides a useful resource of candidate genes for some of the disorders assigned to this region of the X chromosome.
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PMID:Transcript map of the human chromosome Xq11-Xq21 region: localization of 33 novel genes and one pseudogene. 1041 31

The EZH2 gene is a homolog of the Drosophila Polycomb group (PcG) gene enhancer of zest, a crucial regulator of homeotic gene expression. Several lines of evidence suggest a critical role for the EZH2 protein during normal and perturbed development of the haematopoietic and central nervous systems. Indeed, the EZH2 protein has been shown to associate with the Vav proto-oncoprotein and with the XNP protein, the product of a mental retardation gene. The EZH2 gene was previously reported to be located on chromosome 21q22 and was proposed as a candidate gene for some characteristics of the Down syndrome phenotype. We report here the genomic structure and fine mapping of the EZH2 gene. We demonstrate that the functional gene actually maps to chromosome 7q35 and that the sequence previously isolated from a chromosome 21 cosmid corresponds to a pseudogene. Finally, the nature of the EZH2 protein and its mapping to the critical region for malignant myeloid disorders lead us to propose the EZH2 gene is involved in the pathogenesis of 7q35-q36 aberrations in myeloid leukaemia.
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PMID:The human EZH2 gene: genomic organisation and revised mapping in 7q35 within the critical region for malignant myeloid disorders. 1078 Jul 82

Williams syndrome (WMS) is a most compelling model of human cognition, of human genome organization, and of evolution. Due to a deletion in chromosome band 7q11.23, subjects have cardiovascular, connective tissue, and neurodevelopmental deficits. Given the striking peaks and valleys in neurocognition including deficits in visual-spatial and global processing, preserved language and face processing, hypersociability, and heightened affect, the goal of this work has been to identify the genes that are responsible, the cause of the deletion, and its origin in primate evolution. To do this, we have generated an integrated physical, genetic, and transcriptional map of the WMS and flanking regions using multicolor metaphase and interphase fluorescence in situ hybridization (FISH) of bacterial artificial chromosomes (BACs) and P1 artificial chromosomes (PACs), BAC end sequencing, PCR gene marker and microsatellite, large-scale sequencing, cDNA library, and database analyses. The results indicate the genomic organization of the WMS region as two nested duplicated regions flanking a largely single-copy region. There are at least two common deletion breakpoints, one in the centromeric and at least two in the telomeric repeated regions. Clones anchoring the unique to the repeated regions are defined along with three new pseudogene families. Primate studies indicate an evolutionary hot spot for chromosomal inversion in the WMS region. A cognitive phenotypic map of WMS is presented, which combines previous data with five further WMS subjects and three atypical WMS subjects with deletions; two larger (deleted for D7S489L) and one smaller, deleted for genes telomeric to FZD9, through LIMK1, but not WSCR1 or telomeric. The results establish regions and consequent gene candidates for WMS features including mental retardation, hypersociability, and facial features. The approach provides the basis for defining pathways linking genetic underpinnings with the neuroanatomical, functional, and behavioral consequences that result in human cognition.
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PMID:VI. Genome structure and cognitive map of Williams syndrome. 1095 36

Two healthy sisters with a familial history of mental retardation were referred to our centre for preimplantation genetic diagnosis (PGD). Their two brothers showed severe mental retardation. The molecular basis for their disorder could not be identified, but one of the sisters and the mother presented a highly skewed pattern of X-inactivation reinforcing the likelihood of an X-linked mode of inheritance. Both sisters requested PGD to avoid the abortion of potentially affected male fetuses. PGD for sex by fluorescent in-situ hybridization was carried out for the first sister and resulted in the birth of a female child. The second sister and her partner, whose niece had cystic fibrosis (CF), were tested for CF mutations, and were both found to be deltaF508 heterozygous. We developed an efficient single cell PCR protocol for the simultaneous amplification of the CF (deltadeltaF508) locus as well as the X-linked amelogenin gene and its highly homologous pseudogene on the Y chromosome. Two PGD cycles were carried out to screen against male and deltaF508 homozygous deleted embryos. In each case several embryos could be selected for transfer and the second cycle resulted in a twin pregnancy followed by the birth of two healthy female infants.
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PMID:Birth of healthy female twins after preimplantation genetic diagnosis of cystic fibrosis combined with gender determination. 1208 85

Detailed analyses of 20 patients with sporadic neurofibromatosis type 1 (NF1) microdeletions revealed an unexpected high frequency of somatic mosaicism (8/20 [40%]). This proportion of mosaic deletions is much higher than previously anticipated. Of these deletions, 16 were identified by a screen of unselected patients with NF1. None of the eight patients with mosaic deletions exhibited the mental retardation and facial dysmorphism usually associated with NF1 microdeletions. Our study demonstrates the importance of a general screening for NF1 deletions, regardless of a special phenotype, because of a high estimated number of otherwise undetected mosaic NF1 microdeletions. In patients with mosaicism, the proportion of cells with the deletion was 91%-100% in peripheral leukocytes but was much lower (51%-80%) in buccal smears or peripheral skin fibroblasts. Therefore, the analysis of other tissues than blood is recommended, to exclude mosaicism with normal cells in patients with NF1 microdeletions. Furthermore, our study reveals breakpoint heterogeneity. The classic 1.4-Mb deletion was found in 13 patients. These type I deletions encompass 14 genes and have breakpoints in the NF1 low-copy repeats. However, we identified a second major type of NF1 microdeletion, which spans 1.2 Mb and affects 13 genes. This type II deletion was found in 8 (38%) of 21 patients and is mediated by recombination between the JJAZ1 gene and its pseudogene. The JJAZ1 gene, which is completely deleted in patients with type I NF1 microdeletions and is disrupted in deletions of type II, is highly expressed in brain structures associated with learning and memory. Thus, its haploinsufficiency might contribute to mental impairment in patients with constitutional NF1 microdeletions. Conspicuously, seven of the eight mosaic deletions are of type II, whereas only one was a classic type I deletion. Therefore, the JJAZ1 gene is a preferred target of strand exchange during mitotic nonallelic homologous recombination. Although type I NF1 microdeletions occur by interchromosomal recombination during meiosis, our findings imply that type II deletions are mediated by intrachromosomal recombination during mitosis. Thus, NF1 microdeletions acquired during mitotic cell divisions differ from those occurring in meiosis and are caused by different mechanisms.
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PMID:High frequency of mosaicism among patients with neurofibromatosis type 1 (NF1) with microdeletions caused by somatic recombination of the JJAZ1 gene. 1525 18

Recent studies and advances in high-density oligonucleotide arrays have shown that microdeletions and microduplications occur at a high frequency in the human genome, causing various genetic conditions including mental retardation. Thus far little is known about the pathways leading to this disease, and implementation of microarrays is hampered by their increasing cost and complexity, underlining the need for new diagnostic tools. The aim of this study was to introduce a new targeted platform called "chromosome X exon-specific array" and to apply this new platform to screening of 20 families (including one blind positive control) with suspected X-linked mental retardation, to identify new causative X-linked mental retardation genes. The new microarray contains of 21,939 oligonucleotides covering 92.9% of all exons of all genes on chromosome X. Patient screening resulted in successful identification of the blind positive control included in the sample of 20 families, and one of the remaining 19 families was found to carry a 1.78-kilobase deletion involving all exons of pseudogene BRAF2. The BRAF2 deletion segregated in the family and was not found in 200 normal male samples, and no copy number variations are reported in this region. Further studies and focused investigation of X-linked disorders have the potential to reveal the molecular basis of human genetic pathological conditions that are caused by copy-number changes in chromosome X genes.
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PMID:A new chromosome x exon-specific microarray platform for screening of patients with X-linked disorders. 1977 34