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 (…
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…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.