TAC3 and hypogonadotropic hypogonadism: In humans, the neuropeptides kisspeptin and neurokinin B (NKB) have been identified as major activators of pulsatile GnRH secretion, with loss-of-function mutations in KISS1 (encoding kisspeptin) and TAC3 (encoding NKB) genes associated with hypogonadotropic hypogonadism (HH) (11–15).