Klinefelter syndrome in adolescence: onset of puberty is associated with accelerated germ cell depletion.

The process of germ cell depletion in patients with Klinefelter syndrome (KS) is incompletely characterized. In the current work, we evaluated the presence of germ cells in adolescent boys with KS for possible future use in assisted reproduction techniques. Fourteen nonmosaic 47,XXY boys (aged 10-14 yr) were enrolled. Every fourth month their puberty was staged, and serum was obtained for hormone analyses. Each boy underwent a single testicular biopsy. Biopsy specimens of seven peripubertal boys (testicular volume < 2.0 ml) had spermatogonia of adult type, whereas older boys with larger testes (> 2.0 ml) exhibited no germ cells. No meiotic germ cells were detectable in any of these subjects. Depletion of germ cells was associated with an increase in testicular volume but was not immediately reflected in levels of serum gonadotropin, inhibin B, or anti-Müllerian hormone. In contrast, hypergonadotropism and suppression of serum inhibin B and anti-Müllerian hormone developed later, during midpuberty, after an unequivocal increase in serum testosterone (>2.5 nmol/liter) levels and degeneration of Sertoli cells. In conclusion, these prepubertal and early pubertal boys with KS had diploid germ cells that vanished in early puberty when testicular volume increased, whereas serum gonadotropin and inhibin B levels displayed pathological changes later during midpuberty.