They are required for multiple processes during embryogenesis, and dysregulation is linked to cancer and many congenital diseases such as Kallmann syndrome, which affects differentiation of gonadotrophin-releasing hormone (GnRH) neurons (GnRH is a hypothalamic neuropeptide required for reproductive development and function) resulting in hypogonadism (for review, see Chung & Tsai (2010)). Here, GNRH1 is linked to cancer.