Molecular screening of intellectually disabled patients and those with premature ovarian failure for CGG repeat expansion at FMR1 locus: Implication of combined triplet repeat primed polymerase chain reaction and methylation-specific polymerase chain reaction analysis.

Abstract

Fragile X syndrome (FXS) is also a leading cause of intellectual disability along with Down's syndrome. It is caused by the expansion of CGG triplet repeat at 5' untranslated region of the fragile X mental retardation 1 (FMR1) gene. Since the prevalence rate is quite high in the general population, molecular diagnosis is important to establish the cause and the prenatal diagnosis. At present, there are a number of methods available with their own merits and demerits. Molecular screening of intellectually disabled patients and those with premature ovarian failure with combined triplet repeat primed polymerase chain reaction (TP-PCR) and methylation-specific polymerase chain reaction (MS-PCR) for establishing the diagnosis of FXS. The specificity of the method has been validated with archived previously genotyped samples, facilitating the application of this method in the screening procedure. The combined TP-PCR and MS-PCR approach identified six (10%) of the intellectually disabled cases as full mutation positive, one (4%) of the premature ovarian failure cases as premutation positive, and one (out of two) of the prenatal samples as premutation positive. The present study concludes that a combined usage of TP-PCR and MS-PCR will be a useful alternative approach to diagnose patients suffering from fragile X syndrome.