TAC3 and hypogonadotropic hypogonadism: Mutations in the genes encoding for kisspeptin, NKB, and their receptors (KISS1, TAC3, KISS1R, TACR3) result in hypogonadotrophic hypogonadism (1, 2, 11), indicating that both kisspeptin and NKB are critical for normal GnRH secretion in humans and subsequent puberty and reproduction.