[Molecular cytogenetics of fragile X syndrome]

Fragile X syndrome is the most common heritable form of mental retardation, and affects 1 in 1500(male)-2500(female), with minor dysmorphic manifestations such as long face with large protruding ears and macro-orchidism in mentally retarded male patients. The syndrome is caused by dynamic mutation(trinucleotide repeat expansion) at FRAXA located on the long arm of X chromosome. Molecular diagnosis enables carrier identification as well as prenatal diagnosis, in which the cytogenetic method was not feasible. Premutation in phenotypically normal carriers and full mutation in mentally retarded patients explain the characteristic inheritance of the disease called anticipation. This article describes the recent advancements in molecular cytogenetics of fragile X syndrome.