Type 1 is the X-linked form with mutations of gene Kal1 which encodes anosmin-1 protein that plays a key role in the migration of GNRH-containing neurons and olfactory nerves to the HYPOTHALAMUS.

Type 2 is an autosomal dominant form with loss-of-function mutations of gene Kal2 which encodes fibroblast growth-factor receptor-1 (FGFR1 PROTEIN).

A genetically heterogeneous disorder caused by hypothalamic GNRH deficiency and OLFACTORY NERVE defects. It is characterized by congenital HYPOGONADOTROPIC HYPOGONADISM and ANOSMIA, possibly with additional midline defects. It can be transmitted as an X-linked (GENETIC DISEASES, X-LINKED), an autosomal dominant, or an autosomal recessive trait.