title: [Pathology of unstable sequence of genome: fragile-X-syndrome].
abstract: Fragile X syndrome is the most frequent form of inherited mental retardation and is associated with a fragile site at Xq27-3. This fragile site is an unstable microsatellite repeat, p(CCG). In fragile X syndrome families, this sequence exhibits variable amplification, the length of which correlates with phenotype. Affected persons have both a "full mutation" and abnormal DNA methylation. Subjects with smaller increase of this sequence, called "premutation", have little or no risk retardation, but are at high risk of having affected children or grandchildren. The passage from "premutation" to "full mutation" status occurs only with transmission from the mother. The unusual segregation patterns in fragile X pedigrees is referred to as the Sherman paradox, now elucidated by genotypic analysis. We present here a brief review of this pathology and illustrate the use of this new diagnostic test in our laboratory.
authors.affiliation: Laboratoire de Biochimie Génétique, Paris.
authors.forename: C
authors.initials: C
authors.lastname: Beldjord
authors.forename: L
authors.initials: L
authors.lastname: Richard
mesh_terms: D004247:DNA / Q000235:genetics; D005260:Female; D005600:Fragile X Syndrome / Q000175:diagnosis / Q000235:genetics*; D006801:Humans; D008297:Male; D009154:Mutation / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics
chemical_list: D004247:DNA
vernacular_title: Pathologie d'une région instable du génome: le syndrome X-fragile.