[Analysis and prenatal diagnosis of FMR1 gene mutations among patients with unexplained mental retardation].

Objective: To analyze the (CGG)n repeats of FMR1 gene among patients with unexplained mental retardation.
Methods: For 201 patients with unexplained mental retardation, the (CGG)n repeats of the FMR1 gene were analyzed by PCR and FragilEase ^TM PCR. Prenatal diagnosis was provided to carriers of pre- and full-mutations. The pattern of X chromosome inactivation (XCI) was determined for women with mental retardation and full mutations.
Results: For the 201 patients with unexplained mental retardation, 15 were identified with full mutations of the FMR1 gene. The prevalence of fragile X syndrome (FXS) in patients with unexplained mental retardation was determined as 7.5% (15/201). Prenatal diagnosis was provided for 6 pregnant women with pre- or full mutations. Analysis revealed that women with mental retardation and full FMR1 mutations exhibited a skewed XCI pattern with primary expression of the X chromosome carrying the mutant allele.
Conclusion: FXS has a high incidence among patients with unexplained mental retardation. Analysis of FMR1 gene (CGG)n repeats in patients with unexplained mental retardation can facilitate genetic counseling and prenatal diagnosis for their families. FMR1 gene (CGG)n repeats screening should be recommended for patients with unexplained mental retardation.