Human Reproduction Update Advance Access originally published online on September 19, 2005
Human Reproduction Update 2006 12(1):39-48; doi:10.1093/humupd/dmi039
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Natural history of seminiferous tubule degeneration in Klinefelter syndrome
1 Department of Growth and Reproduction, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark, 2 Hospital for Children and Adolescents, Helsinki University Central Hospital, University of Helsinki, Helsinki and 3 Department of Pediatrics, Kuopio University Hospital, University of Kuopio, Kuopio, Finland
4 To whom correspondence should be addressed at: Department of Growth and Reproduction, Rigshospitalet Section 5064, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark. E-mail: ajuul{at}rh.dk
Submitted on June 15, 2005; revised on August 1, 2005; accepted on August 15, 2005
Klinefelter syndrome (47,XXY) is characterized by small, firm testis, gynaecomastia, azoospermia and hypergonadotropic hypogonadism. Degeneration of the seminiferous tubules in 47,XXY males is a well-described phenomenon. It begins in the fetus, progresses through infancy and accelerates dramatically at the time of puberty with complete hyalinization of the seminiferous tubules, although a few tubules with spermatogenesis may be present in adult life. Activation of the pituitary-gonadal axis at 3 months of age is seen in Klinefelter boys similar to healthy boys. However, the level of testosterone in Klinefelter boys is significantly lower than in controls. After this ‘minipuberty’, the hormone levels decline to normal prepubertal levels until puberty. In puberty, an initial rise in testosterone, inhibin B, LH and FSH occurs in Klinefelter boys. However, the rise in testosterone levels off and ends at a low-normal level in young adults. Likewise, serum concentration of inhibin B exhibits a dramatic decline to a low, often undetectable level, concomitantly with a rise in FSH, reflecting the degeneration of the seminiferous tubules. Many hypotheses about the underlying mechanism of the depletion of the germ cells in Klinefelter males have been reported and include insufficient supranumerary X-chromosome inactivation, Leydig cell insufficiency and disturbed regulation of apoptosis of Sertoli and Leydig cells. However, at present, the exact mechanism remains unclear. In this article, we summarize current knowledge on the development of the classical endocrinological and histological features of 47,XXY males from fetus to adulthood and review the literature concerning the degeneration of the seminiferous tubules in this syndrome.
Key words: azoospermia / infertility / Klinefelter syndrome / Sertoli cells / testes
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