Prenatal diagnosis of fragile X syndrome: Small meiotic recombination events at the FMR1 locus

Abstract

What's already known about this topic? Fragile X syndrome is caused by an expansion of more than 200 CGG repeats in the FMR1 gene. CGG repeat instability expresses almost constantly as an expansion. Significant contraction events have occasionally been reported. What does this study add? This study presents an exceptional situation, where maternal transmission of an FMR1‐expanded allele ultimately results in the presence of a normal‐sized allele in the fetus. We report here two prenatal cases of non‐crossover event at the FMR1 locus. We offer an algorithm to be used in the context of fragile X syndrome prenatal diagnosis.