An genetic condition in which there is a lack of gonadotropin-releasing hormone (GnRH). This hormone produced in the hypothalamus, regulates the release of the other hormones in the pituitary gland that in turn stimulate the testes. The deficiency of GnRH prolongs or occasionally prevents normal sexual development at puberty. The condition is also linked with colour blindness, and a lack of sense of smell. Treatment is administered with hormones that replace GnRH.