OBJECTIVETo assess the value of genetic testing for Fragile X syndrome (FXS).

METHODSA domestically made diagnostic kit based Tri-primer-PCR method was used to detect mutations of the FMR1 gene among 6 pedigrees with unexplained intellectual disability. The results were verified by methylation PCR and Southern blotting.

RESULTSPedigrees 1 and 6 were positive for the screening. In pedigree 1, a full-mutation allele with methylation was identified in the proband and his mother, which was passed on to the fetus. In pedigree 6, the proband was mosaic for a full-mutation allele and a pre-mutation allele. His sister was asymptomatic with a full-mutation. His mother carried pre-mutation allele, while his father and sister's baby were normal. The number of CGG repeats of the pedigrees 2 to 5 were in the normal range.

CONCLUSIONGenetic testing can provide an effective way to prevent FXS caused by FMR1 mutations and enable prenatal diagnosis for families with a high risk for the disease.