We have identified a gene regulatory network, Gsx1/2 – Dlx1/2/5/6 – GAD2/1/Sp8/Sp9 – Tshz1 – Prokr2, which governs OBiN development [39, 84–88]; mutations of some of these genes result in human Kallmann syndrome with abnormal olfactory function (anosmia or hyposmia) [89, 90]. Here, SP9 is linked to Kallmann syndrome.