Similar to kisspeptin, the loss-of-function mutation in neurokinin B (NKB; also known as tachykinin 3 (Tac3)) or of its receptor (NKBR, Tac3R, NK3R) also exhibit hypogonadotropic hypogonadism in humans [9]. Here, TAC3 is linked to hypogonadotropic hypogonadism.