title: The fragile X syndrome.
abstract: An amplification of a highly unstable DNA element has been identified at the fragile X locus in Xq27.3. This sequence appears to be both the source of the primary mutation causing the fragile X syndrome, apparently having its causative effect through the methylation of the FMR-1 HTF island and the region of cytogenetic fragility. The direct analysis of the genotype of carrier and affected individuals can be used as a direct diagnosis tool which will improve both the accuracy and speed of diagnosis. The identification of hereditary unstable DNA in a disease with such a wide level of non-penetrance and variable phenotype may give clues as to the basis of non-penetrance in other human genetic disorders.
authors.forename: M C
authors.initials: MC
authors.lastname: Hirst
authors.forename: S J
authors.initials: SJ
authors.lastname: Knight
authors.forename: M V
authors.initials: MV
authors.lastname: Bell
authors.forename: M
authors.initials: M
authors.lastname: Super
authors.forename: K E
authors.initials: KE
authors.lastname: Davies
mesh_terms: D002873:Chromosome Fragility; D004247:DNA / Q000235:genetics; D005260:Female; D005600:Fragile X Syndrome / Q000175:diagnosis / Q000235:genetics*; D005784:Gene Amplification; D006580:Genetic Carrier Screening / Q000379:methods; D008040:Genetic Linkage; D005819:Genetic Markers; D006801:Humans; D008297:Male; D009154:Mutation / Q000235:genetics
chemical_list: D005819:Genetic Markers; D004247:DNA