KISS1 and hypogonadotropic hypogonadism: Loss-of-function mutations in the genes encoding for kisspeptin (Kiss1) or its receptor (Kiss1r) or NKB (encoded by the Tac2 gene) and its receptor (NK3R, encoded by the Tacr3 gene) in humans and mice, are linked to hypogonadotropic-hypogonadism and infertility (Seminara et al., 2003; Topaloglu et al., 2009).