Hypogonadotropic hypogonadism.

This article outlines the changing pattern of gonadotropin-releasing hormone (GnRH)-induced gonadotropin secretion across sexual development, a knowledge of which is critical to understanding GnRH secretion in pathologic states such as hypogonadotropic hypogonadism. The clinical presentation, differential diagnosis, and treatment of hypogonadotropic hypogonadism in humans are discussed. Particular emphasis is placed on the contribution of frequent sampling studies of gonadotropin secretion and genetic studies to understanding the pathophysiology and clinical heterogeneity of isolated GnRH deficiency in humans.