Rarer syndromes characterized by hypogonadotropic hypogonadism

Hypogonadotropic hypogonadism (HH) secondary to hypothalamic gonadotropin-releasing hormone deficiency is a notable feature of a number of rare syndromes, where unlike idiopathic (isolated) HH, other endocrinopathies may also be apparent. The presence of a particular spectrum of clinical features in addition to HH may suggest a particular underlying diagnosis. Placing the diagnosis of HH into that context will then have important implications in terms of management and predicting long-term functional outcome. In some instances, establishing the genetic basis of a particular syndrome or disorder has advanced the understanding of normal hypothalamo-pituitary-gonadal function (e.g. LEP deficiency, DAX-1 and CHARGE syndrome) whilst in other disorders much has still to be learnt (e.g. Bardet-Biedl and Prader-Willi syndrome). In this chapter the above syndromes, where HH is a feature in most or all affected individuals, will be discussed. Recent advances in our understanding of the pathophysiology of the HH will be highlighted and management options presented. Longer term therapy with sex steroid replacement is becoming even more important if improvements in life expectancy are to be matched by improvements in quality of life.