27). In marked contrast, TP-PCR (Ref. 15) resolves zygosity issues in females by generating a characteristic extended TP-PCR amplicon peak pattern in the presence of an FMR1 expansion, regardless of repeat size. Although routinely used in diagnostic testing for fragile X syndrome (Refs 16–20), FMR1 TP-PCR for single-cell fragile X syndrome PGD has not been reported. Here, FMR1 is linked to fragile X syndrome.