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)

DNA repeat expansion is the genetic basis for a growing number of neurological disorders. While the largest subset of these diseases results in an increase in the length of a polyglutamine tract in the protein encoded by the affected gene, the most common form of inherited mental retardation, fragile X syndrome, and the most common inherited ataxia, Friedreich's ataxia, are both caused by expansions that are transcribed but not translated. These expansions both decrease expression of the gene in which the expanded repeat is located, but they do so by quite different mechanisms. In fragile X syndrome, CGG. CCG expansion in the 5' untranslated region of the FMR1 gene leads to hypermethylation of the repeats and the adjacent CpG-rich promoter. Methylation prevents the binding of the transcription factor alpha-Pal/NRF-1, and may indirectly affect the binding of other factors via the formation of transcriptionally silent chromatin. In Friedreich's ataxia, GAA. TTC expansion in an intron of the FRDA gene reduces expression by interfering with transcription elongation. The model that best describes the available data is transcription-driven formation of a transient purine. purine. pyrimidine DNA triplex behind an advancing RNA polymerase. This structure lassoes the RNA polymerase that caused it, trapping the enzyme on the template.
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PMID:Fragile X syndrome and Friedreich's ataxia: two different paradigms for repeat induced transcript insufficiency. 1171 74

An extended 5-generation family has been investigated in which 32 of the 111 family members were diagnosed as having retinitis pigmentosa (RP). The proband was a 58-year old male in whom night-blindness was first observed in early childhood, with almost loss of vision by 52 years of age. The symptoms observed in other family members included night-blindness, impaired vision and visual field loss. Dementia, digital abnormalities, deaf-mutism and mental retardation were variously diagnosed in a number of individuals with RP. The affected and unaffected family members were tested for mutations in a range of candidate genes. The 8 exons of three candidate genes have been analyzed by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and DNA sequencing techniques. A novel mutation was identified in the rhodopsin gene at codon 52 of exon 1 (TTC-TAC) that resulted in a substitution of Phe to Tyr.
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PMID:Mutation identification in a 5-generation pedigree with autosomal dominant retinitis pigmentosa. 1452 23

Friedreich ataxia, myotonic dystrophy type 1 and 3 forms of intellectual disability, fragile X syndrome, FRAXE mental retardation, and FRA12A mental retardation are repeat expansion diseases caused by expansion of CTG.CAG, GAA.TTC, or CGG.CCG repeat tracts. These repeats are transcribed but not translated. They are located in different parts of different genes and cause symptoms that range from ataxia and hypertrophic cardiomyopathy to muscle wasting, male infertility, and mental retardation, yet recent reports suggest that, despite these differences, the repeats may share a common property, namely the ability to initiate repeat-mediated epigenetic changes that result in heterochromatin formation.
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PMID:Chromatin remodeling in the noncoding repeat expansion diseases. 1895 31