14). In contrast, the triplet-primed PCR (TP-PCR) method (Ref. 15) enables consistent detection of FMR1 expansions from both sexes and effectively resolves zygosity issues in females, and is thus applicable to all couples even if their normal alleles are uninformative. TP-PCR has been used in routine fragile X syndrome molecular diagnostic testing (Refs 16–20) and has been applied in the PGD of myotonic dystrophy type 1, another trinucleotide repeat hyperexpansion disorder (Refs 8, 15, 21), but has not been reported for fragile X syndrome PGD. This evidence concerns the gene FMR1 and fragile X syndrome.