Kisspeptin (Kiss1) is essential for sexual maturation because inactivating mutations in Kiss1 (1) or its receptor (Kiss1r) (2, 3) result in a lack of puberty and hypogonadotropic hypogonadism, and activating mutations cause precocious puberty (4, 5). This evidence concerns the gene KISS1 and hypogonadotropic hypogonadism.