Introduction Fragile X syndrome is the most common cause of inherited mental retardation, seen in approximately one in 1,200 males and one in 2,500 females. Males with fragile X syndrome usually have mental retardation and often exhibit characteristic physical features and behavior [Hagerman and Silverman, 1991; Warren and Nelson, 1994]. Affected females exhibit a similar, but usually less severe phenotype. The diagnosis of fragile X syndrome was originally based on the expression of a folate-sensitive fragile site at Xq27.3 (…showed first 75 words of 1406 total…

…showed last 75 words of 1406 total…because the methylation status of the FMR1 gene is often not yet established in chorionic villi at the time of sampling. CVS, while a standard technique for prenatal diagnosis, may lead to a situation where follow-up amniocentesis is necessary to resolve an ambiguous result. References Hagerman RJ, Silverman AC (1991): "Fragile X syndrome: Diagnosis, Treatment, and Research." Baltimore: Johns Hopkins University Press. Warren ST, Nelson DL (1994): Advances in molecular analysis of fragile X syndrome. JAMA 271:536-542.