FAAH2 and Turner syndrome: The second X-chromosome locus, in Xp11.21 (lead SNP rs5914101 is intronic in FAAH2, MAF 24%, β=0.05 years per allele, P=1.9 × 10−10; Supplementary Fig. 4), lies within the critical region for Turner's syndrome, which is the most common cause of primary ovarian insufficiency20.