Kallmann's syndrome and normosmic isolated hypogonadotropic hypogonadism: two largely overlapping manifestations of one rare disorder

Central hypogonadism (CHg) is a disorder caused by an insufficient GnRH stimulation of an otherwise intact pituitary–gonadal axis. It is also called isolated or congenital gonadotropin-releasing hormone (GnRH) deficiency or isolated hypogonadotropic hypogonadism (IHH). CHg may be either congenital or acquired, and can either be secondary to hypothalamic or pituitary dysfunctions. Isolated CHg is a rare disease with an incidence of 1:8,000 males and 1:40,000 females. It can either be associated with a normal or defective sense of smell, respectively, identifying the normosmic CHg (nCHg or nIHH) or the Kallmann’s syndrome (KS). Males frequently present with defective androgenization and growth at peripubertal age but micropenis and cryptorchidism may already be evident in the neonatal period, indicating a defective HPG activation during the prenatal development. Females generally present with primary amenorrhea and growth retardation.