High in the hierarchy of such inputs to GnRH neurons is the kisspeptin system, since the cognate GPR54 receptor is one of the few receptors to be abundantly expressed by GnRH neurons (Messager et al., 2005), and because congenital absence of kisspeptin or GPR54 in man or targeted ablation of these in mice results in complete infertility (d'Anglemont de Tassigny et al., 2007; Seminara et al., 2003). The gene discussed is GNRH1; the disease is Infertility.