Prenatal Population Screening for Fragile X Carrier and the Prevalence of Premutation Carriers in, Korea

Purpose: Fragile X carrier detection before or at early pregnancy through a wide screening program may not only confer a risk of having offspring with Fragile X syndrome (FXS), but may also confer a risk for Fragile X-associated primary ovarian insufficiency and Fragile X-associated tremor/ataxia syndrome. However, prior to the implementation of such a program, the carrier prevalence in a population and the availability of effective screening test should be evaluated. The aim of our study was to determine the prevalence of premutation carriers and to evaluate the feasibility of screening test. Materials and Methods: The blood samples were obtained from 8,641 pregnant women with no family history of mental retardation. We performed a three-primer CGG repeat primed (RP) PCR using the AmplideX$^{TM}$ FMR1 PCR kit (Asuragen, Inc. Austin, TX, USA). Samples showing full mutation alleles were reflexed to Southern blot analysis for methylation status and sizing. Results: Among the 8,641 women, we found 8 premutation carriers (1:1,090, 0.09%) and 46 women with an intermediate allele (1:190, 0.53%). No woman was found to carry the fully mutated allele. All the detected alleles were within the CGG repeat range of 8-117. Among the 8,641 samples, 29 and 30 CGG repeats represent 66.6% of all cases. The CGG RP PCR method provides robust detection of expanded alleles and resolves allele zygosity, thus minimizing the number of samples that require Southern blot analysis. Conclusion: This is the first study that has focused on the prevalence of FXS premutation carriers and FMR1 allele distribution in normal pregnant women. These data have important implications for population-based fragile X carrier screening in Korea.