In the mouse, targeted genetic disruption of GPR54 (de Roux et al., 2003; Funes et al., 2003; Seminara et al., 2003) or of Kiss1 (d’Anglemont de Tassigny et al., 2007; Lapatto et al., 2007) produce a similar hypogonadotropic hypogonadism phenotype, suggesting that kisspeptins represent the main ligands for this receptor. The gene discussed is KISS1; the disease is hypogonadotropic hypogonadism.