GNRH1 and Kallmann syndrome: Kallmann syndrome (KS) is a genetically heterogeneous disorder characterized by isolated hypogonadotropic hypogonadism (IHH) with anosmia or hyposmia, caused by defective migration of olfactory and gonadotropin-releasing hormone (GNRH) neurons from the olfactory placode region across the cribriform plate to the bulb (1).