Strategy for reliable prenatal detection of normal male carriers of the fragile X syndrome.

Prenatal diagnosis of fragile X syndrome identifying full mutations has been described. Here we report on a case of a prenatal test concerning a normal male carrier of the fragile X syndrome. Southern blot analysis of the fragile X gene resulted in the identification of a premutation in DNA isolated from the chorionic villus sample. Using a polymerase chain reaction (PCR)-based assay the CGG repeat length was determined to be 82 CGG repeat units. Confirmation of this premutation in the chorionic villus sample was based on the cytogenetic analysis of the expression of the fragile site at Xq27 applied on a cordocentesis-derived blood sample.