Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mutations at FRAXA and FRAXE loci are due to expansions of a CGG trinucleotide repeat and are characterized by mental retardation. Here we report a pilot screening survey by means of cytogenetic and molecular methods of 433 unrelated retarded individuals and their parents of Hellenic origin coming from various parts of Greece and Cyprus. The purpose of the study was to estimate the frequency of FRAXA mutation in individuals with nonspecific mental retardation without family history and phenotypic stigmata in the Hellenic population. Five FRAXA-positive children (1.15%) were identified, of whom four were found to carry a full mutation and one a premutation. Furthermore we present preliminary data on a screening of FRAXE mutation frequency. We screened 257 male patients with nonspecific mental retardation, finding none positive for FRAXE mutation.
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PMID:FRAXA and FRAXE prevalence in patients with nonspecific mental retardation in the Hellenic population. 952 14

Fragile X (FraX) syndrome is the most common cause of inherited mental retardation. To see whether FRAXA or FRAXE can account for the etiology of some unexplained neurodevelopmental disorders in children, we screened for trinucleotide repeat expansion in a consecutive cohort of 73 Chinese children and their mothers seen in 1995 (group 1) referred for developmental assessment due to developmental delay, language delay, attention deficit hyperactivity disorder, autistic spectrum disorder, mental retardation and/or learning disability. We also screened DNA samples of all five previously diagnosed cytogenetically-positive FraX boys, their mothers and sisters (group 2). A control group of unrelated teenagers and adults were recruited from the community (group 3). In group 1, 3 families (2 mothers and a mother and her son) were found to carry a small premutation allele at FRAXA (premutation frequency = 2%, 3/153 independent X chromosomes), but none had any expansion at FRAXE. In group 2, all 5 FraX boys had full mutation at FRAXA and normal repeat length at FRAXE. In group 3, 1 male has a premutation allele out of 18 males and 59 females tested (premutation frequency of control = 0.7%, 1 out of 136 X chromosomes). For FRAXE screening in group 3, 2 females were carriers (1.5%, 2 out of 136 X chromosomes). Thus, FRAXA and FRAXE cannot account for the etiology of neurodevelopmental disorders in our cohort of Chinese children, and the prevalence of FRAXE mutation in normal Chinese population appears to be higher than reported in the Caucasians.
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PMID:DNA diagnosis of FRAXA and FRAXE in Chinese children with neurodevelopmental disorders and fragile X syndrome. 963 71

FRAXA, FRAXE, and FRAXF are folate-sensitive fragile sites originally discovered in patients with X-linked mental retardation. The FMR1 gene, whose first exon includes the FRAXA site on Xq27.3, accounts for 15-20% of all X-linked forms of mental retardation. Loss of expression of FMR2, a gene adjacent to the FRAXE site on Xq28, is correlated with FRAXE expansion in some mild mentally retarded patients. FRAXF is a fragile site whose expression has not been associated with any pathological phenotype. The fragility in all three sites is caused by expansions of CGG repeats adjacent to hypermethylated CpG islands. The prevalence of FRAXA, FRAXE, and FRAXF remains uncertain because of the lack of a simple and cost-effective test allowing wide screening programs. For the same reason, the real phenotype-genotype correlations in FRAXE and FRAXF are uncertain as well. We have developed a rapid multiplex polymerase chain reaction (PCR) assay in which hypermethylated CpG islands adjacent to FRAXA, FRAXE, and FRAXF are displayed. The test is very simple and cost-effective, requires only 30 microl of peripheral blood, and can be used for performing diagnoses, postnatal and prenatal, and for screening large groups of control and mentally retarded males and newborn boys.
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PMID:A simple multiplex FRAXA, FRAXE, and FRAXF PCR assay convenient for wide screening programs. 1009 54

FMR2 is the gene associated with FRAXE fragile site non-specific mental retardation (FRAXE MRX). Previously a male patient was identified with developmental delay and speech problems who had a deletion within intron 3 of FMR2. No known FMR2 exonic sequences were missing in this patient. Detailed northern blot analysis revealed existence of a new large isoform of FRM2 in foetal brain. This isoform was characterised and found to be due entirely to an addition of an extra 4.9 kb of the 3' UTR to the previously characterised 8.755 kb FMR2 transcript. This excluded involvement of the large FMR2 isoform in the MRX phenotype of three individuals now known to have the same deletion of intron 3 FMR2 sequences. Expression studies on the new 13.7 kb FMR2 isoform show that it is expressed predominantly in foetal brain and adult pituitary gland, whilst the expression of the shorter previously characterised 8.755 kb isoform is broader, including testis, thymus and placenta. Possible consequences of the alternative processing and expression of FMR2 for the molecular pathology of FRAXE MRX are discussed.
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PMID:Characterisation and expression of a large, 13.7 kb FMR2 isoform. 1019 98

The folate sensitive fragile site FRAXE is located in Xq28, 600 kb distal to the fragile X syndrome (FRAXA) fragile site. An unstable GCC triplet repeat responsible for FRAXE exists in the 5' untranslated region of FMR2 gene. Normal alleles range from 10-35 repeats and more frequently 15-20 GCCs. An expanded GCC repeat over 200 is methylated, inactivates FMR2, and results in FRAXE mental retardation. Affected individuals show mild mental retardation and/or autistic symptoms FMR2 is a large gene consisting of 21 exons spanning about 600 kb. FMR2 mRNA is about 9.5 kb and is expressed in the brain(especially in the hippocampus and the amygdala) in adults and also in placenta. The FMR2 protein is 1311 amino acids, contains nuclear localization signals, and is a putative transcription factor.
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PMID:[FRAXE mental retardation]. 1022 96

This study presents the first large, population-based molecular investigation of the fragile X (FRAXA) and FRAXE mental retardation syndromes in the Hellenic populations of Greece and Cyprus. The aims of this population screening were to determine the prevalence of FRAXA and FRAXE syndromes among idiopathic mentally retarded (IMR) individuals, to estimate the incidence in the general population, and to investigate the molecular mechanism of instability and expansion of the FMR1-repeat. Ten FRAXA patients were identified to have either the full mutation (eight) or premutation (two) from a Hellenic population of 866 unrelated IMR individuals (611 males and 255 females, age range 3-25 years). No FRAXE patients were identified among the 611 IMR males. The incidence of FRAXA in the Hellenic population of Cyprus is estimated at 1 in 4,246 males. The repeat sites from the FMR1 and FMR2 alleles were accurately determined and showed similar distribution and frequencies with other population studies. The analysis of AGG interspersion within the FMR1-repeat in normal males revealed long, pure CGG repeats within the "gray zone" as well as variation within the 3' end showing polarity of instability. This finding supports the hypothesis that the AGG interspersion and the length of the pure repeat are major factors in determining allele stability. Analysis of FRAXAC1, DXS548, and FRAXAC2 identified particular alleles and haplotypes to have a significant association with either gray zone alleles or alleles >15 pure CGG repeats. We hypothesize that this subgroup of alleles and haplotypes are associated with long pure CGGs (>15 CGG) or 35 repeats and, having shared an evolutionary past, would have the tendency to expand.
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PMID:Molecular screening of fragile X (FRAXA) and FRAXE mental retardation syndromes in the Hellenic population of Greece and Cyprus: incidence, genetic variation, and stability. 1033 87

The transcriptional silencing of the FMR2 gene has been implicated in FRAXE mental retardation. FRAXE individuals have been shown to exhibit learning deficits, including speech delay, reading and writing problems. FMR2 encodes a large protein of 1311 amino acids and is a member of a gene family encoding proline-serine-rich proteins that have properties of nuclear transcription factors. To characterize the expression of the fragile X mental retardation 2 (FMR2) protein, polyclonal antibodies were raised against two regions of the human FMR2 protein and used in immunofluorescence experiments on mouse brain cryosections. Our results demonstrate for the first time that the FMR2 protein is localized in neurons of the neocortex, Purkinje cells of the cerebellum and the granule cell layer of the hippocampus. FMR2 staining is shown to colocalize with the nuclear stain 4,6-diamidino-2-phenylindole (DAPI) confirming that FMR2 is a nuclear protein. The localization of FMR2 protein to the mammalian hippocampus and other brain structures involved with cognitive function is consistent with the learning deficits seen in FRAXE individuals.
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PMID:Localization of the fragile X mental retardation 2 (FMR2) protein in mammalian brain. 1065 94

Fragile X syndrome is the most common inherited form of mental retardation. The syndrome is associated with a CGG repeat expansion in the 5'UTR of the first exon of the FMR1 gene. This gene maps to Xq27.3 and coincides with the cytogenetic fragile site (FRAXA). The present study deals with the prevalence of fragile X syndrome among individuals with mental retardation of unknown cause from institutions and special schools from the Spanish Basque Country. Results of cytogenetic and molecular studies, performed in a group of 134 unrelated individuals (92 males and 42 females) are presented. The cytogenetic marker at Xq27.3 was identified in 12 patients. Other chromosomal abnormalities were found in two cases that this and previous studies confirmed as Angelman and Prader-Willi syndromes. Two males, in whom the cytogenetic marker was identified, were found negative for FRAXA and FRAXE expansion at the molecular level. The present study shows that the frequency of the FRAXA full mutation in individuals of Spanish non-Basque origin is in the range of other Spanish populations. In the sample of Spanish Basque origin we have not found cytogenetic FRAXA site expression, and the CGG repeat size of FMR1 gene is in the normal range. The significance of these results are discussed.
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PMID:A survey of fragile X syndrome in a sample from Spanish Basque country. 1067 58

The FRAXE fragile site, 600 kb distal to the more common FRAXA, has been reported to be expressed in subjects with mild non-syndromal mental retardation (MR). Amplification of more than 200 GCC repeats, associated with methylation of the adjacent CpG island at Xq28, leads to the expression of the fragile site. In 1996 a large gene, FMR2, transcribed distally from the CpG island and downregulated by repeat expansion and methylation, was identified. Among 232 mentally retarded patients, tested FRAXA negative, we identified an Italian family segregating a hypermethylated expansion at the FRAXE locus in two dizygotic twin brothers, their sister and their mother. The index case was referred at 23 years of age with severe MR, epilepsy, a dysmorphic face with a high arched palate, marfanoid habitus and hyperreflexia of the lower limbs. His brother was referred to as normal and psychometric tests confirmed he is not mentally retarded. All members of the family underwent FRAXE molecular analysis, after cytogenetic expression of the fraX site and negative FRAXA test. Interestingly, an expansion and a hypermethylation at the FRAXE locus were found in all of them. Fibroblasts from the clinically normal brother were assayed for FMR2 expression and the transcription of the gene was found to be silenced. The presence of a phenotypically normal male with absent FMR2 expression in fibroblasts suggests that the relationship between the FRAXE mutation, FMR2 expression and MR needs to be further investigated.
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PMID:FRAXE mutation in a mentally retarded subject and in his phenotypically normal twin brother. 1078 Jul 79

The fragile X syndrome (Fra-X) is the most common cause of inherited mental retardation with X-linked semi-dominant inheritance. The prevalence of Fra-X in the Mexican population is unknown. The aim of this population screening study was to determine if Fra-X or FRAXE mutations are the cause of a number of cases of mental retardation in a sample of Mexican children with mental retardation of unknown cause (MRUC) and to stress the importance of performing molecular analysis of the FMR-1 gene in all patients with MRUC. We report here the direct analysis of CGG and GCC repeats within the FMR-1 and FMR-2 genes, respectively, in 62 unrelated patients with MRUC. Two male index cases had the CGG expansion, although they did not express the Xq27.3 fragile site cytogenetically. Fra-X diagnosis was highly suspected on a clinical basis in one of the patients, but not in the other. Both mothers were found to be premutation carriers. The molecular studies of FMR-1 showed that the proportion of MRUC patients with Fra-X is 3.2%. This frequency was not significantly different to that reported in most populations. As reported in other series, no patients with FRAXE were found in our sample. Our findings confirm that the molecular analysis of the FMR-1 gene is necessary in MRUC patients to achieve unequivocal diagnosis of fragile X syndrome, carrier premutation detection and for accurate genetic counseling.
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PMID:Molecular diagnosis of the fragile X and FRAXE syndromes in patients with mental retardation of unknown cause in Mexico. 1081 18


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