Klinefelter syndrome.

Klinefelter syndrome (KS) is the most common genetic form of male hypogonadism, but overt phenotype becomes evident only after puberty. During childhood, and even during early puberty, pituitary-gonadal function in 47,XXY subjects is relatively normal, but from midpuberty onwards, FSH and LH levels increase to hypergonadotropic levels, inhibin B decreases to undetectable levels, and testosterone levels after some increase plateau at low-normal levels for healthy adult men. Hence, most adult KS males display a clear hypergonadotropism with a varying degree of androgen deficiency; subsequently testosterone substitution therapy is widely used to prevent symptoms and sequels of androgen deficiency. Testicular biopsies of prepubertal KS boys have shown preservation of seminiferous tubules with reduced numbers of germ cells, but Sertoli and Leydig cells have appeared normal. The testes in the adult KS male are characterized by extensive fibrosis and hyalinization of the seminiferous tubules, and hyperplasia of the interstitium. However, the tubules may show residual foci of spermatogenesis. Introduction of testicular sperm extraction (TESE) in combination with intracytoplasmic sperm injection (ICSI) techniques has allowed non-mosaic KS males to father children.