KISS1 and hypogonadotropic hypogonadism: Kisspeptin (encoded by Kiss1 gene) neurons are known to be a key regulator of mammalian reproduction because loss-of-function mutations in the kisspeptin receptor (also known as GPR54) gene result in hypogonadotropic hypogonadism in humans, and deletion of Kiss1 or GPR54 in mice and rats causes infertility in both sexes7–10.