Genetics and hypogonadotrophic hypogonadism.

Hypothalamic pulsatile gonadotrophin-releasing hormone secretion, stimulating pituitary gonadotrophin secretion, is essential for adult reproductive function. This neuroendocrine drive to the reproductive axis is critically dependent on a sequence of developmental events in utero. During early foetal life, gonadotrophin-releasing hormone neurones migrate from the nasal placode to the medial basal hypothalamus where gonadotrophin-releasing hormone can be transported down portal vessels to the anterior pituitary. Gonadotrophin-releasing hormone secretion is active fleetingly neonatally but soon becomes quiescent throughout childhood. At the time of puberty activation of gonadotrophin-releasing hormone secretion reawakens the hypothalamic pituitary-gonadal axis and secondary sexual maturation is triggered. Any disruption in gonadotrophin-releasing hormone secretion will result in hypogonadotrophic hypogonadism. The clinical manifestations of this become apparent with secondary sexual maturation. Genetic mutations have been identified in a minority of cases. These include Kallmann syndrome, adrenal hypoplasia congenital, gonadotropin-releasing hormone receptor and luteinizing hormone or follicle-stimulating hormone beta-subunit gene mutations. The importance of these discoveries is important not only in relation to the conditions that result, but also for our better understanding of normal reproductive function.