6). In addition, ~21% of the premutation females experience fragile X-associated primary ovarian insufficiency (FXPOI) (Ref. 7), a condition that results in infertility and onset of menopause before the age of 40. At-risk couples can avoid fragile X syndrome-affected/carrier pregnancies by preimplantation genetic diagnosis (PGD) of in vitro fertilisation (IVF)-derived embryos and selective transfer of embryo(s) with normal (5−44 CGGs) FMR1 allele(s) for implantation. Here, FMR1 is linked to fragile X syndrome.