FEZF1 and Kallmann syndrome: The disruption in the maturation process of olfactory neurons, which is intertwined with the migration of gonadotropin releasing hormone (GnRH) neurons, is associated with hypogonadotropic hypogonadism 22 with anosmia (also known as Kallmann syndrome) or without anosmia (HH22 [MIM: 616030]), both of which has been linked to missense mutations within FEZF1 [40,41,42].