title: Development of Genetic Testing for Fragile X Syndrome and Associated Disorders, and Estimates of the Prevalence of FMR1 Expansion Mutations.
abstract: The identification of a trinucleotide (CGG) expansion as the chief mechanism of mutation in Fragile X syndrome in 1991 heralded a new chapter in molecular diagnostic genetics and generated a new perspective on mutational mechanisms in human genetic disease, which rapidly became a central paradigm ("dynamic mutation") as more and more of the common hereditary neurodevelopmental disorders were ascribed to this novel class of mutation. The progressive expansion of a CGG repeat in theFMR1gene from "premutation" to "full mutation" provided an explanation for the "Sherman paradox," just as similar expansion mechanisms in other genes explained the phenomenon of "anticipation" in their pathogenesis. Later,FMR1premutations were unexpectedly found associated with two other distinct phenotypes: primary ovarian insufficiency and tremor-ataxia syndrome. This review will provide a historical perspective on procedures for testing and reporting of Fragile X syndrome and associated disorders, and the population genetics ofFMR1expansions, including estimates of prevalence and the influence of AGG interspersions on the rate and probability of expansion.
authors.affiliation: Wessex Regional Genetics Laboratory, Salisbury NHS Foundation Trust, Salisbury District Hospital, Salisbury SP2 8BJ, UK. James.Macpherson@salisbury.nhs.uk.
authors.forename: James N
authors.initials: JN
authors.lastname: Macpherson
authors.affiliation: Medical School, University of Exeter, RILD Level 3, Royal Devon & Exeter Hospital, Barrack Road, Exeter EX2 5DW, UK. A.Murray@exeter.ac.uk.
authors.forename: Anna
authors.initials: A
authors.lastname: Murray
keywords: Fragile X; dynamic mutation; prevalence