title: Klinefelter syndrome: the commonest form of hypogonadism, but often overlooked or untreated.
abstract: BACKGROUND
  Klinefelter syndrome (KS) with the karyotype 47,XXY is one of the commonest types of congenital chromosomal disorder in males, with an incidence of 0.1% to 0.2% of newborn male infants. It causes hypogonadism and infertility. Until now, however, only about one-quarter of all persons with KS received the diagnosis during their lifetimes.
  
  
  METHODS
  Selective review of the literature.
  
  
  RESULTS
  KS is caused by aneuploidy of the sex chromosomes. Small, firm testes, the manifestations of androgen deficiency (sparse development of male-pattern body hair, greater than average height, lack of libido, erectile dysfunction) and, in more than 90% of affected men, azoospermia are its main features in adults. Affected boys may have verbalization difficulties and problems with learning and socialization. KS is often accompanied by other disturbances such as gynecomastia, varicose veins, thrombosis, osteoporosis, the metabolic syndrome, type 2 diabetes, and epilepsy. The most important therapeutic measure is testosterone supplementation, which should be initiated if the testosterone concentration drops below 12 nmol/L and should be given as directed in the guidelines for the treatment of hypogonadism. This recommendation is made even though there have not been any randomized controlled trials documenting the efficacy of testosterone therapy in adolescents or young adults. In some cases, viable sperm can be obtained from individual testicular tubules by biopsy, so that these patients are able to become fathers.
  
  
  CONCLUSIONS
  The diagnosis of KS would be less frequently missed if doctors were more aware of, and attentive to, its key manifestations, particularly the small, firm testes, erectile dysfunction, and the comorbidities mentioned above. If the diagnosis were made more often, patients would more often be able to receive early treatment, which would improve their quality of life.
authors.affiliation: Centre of Reproductive Medicine and Andrology, University of Münster. Eberhard.Nieschlag@ukmuenster.de
authors.forename: Eberhard
authors.initials: E
authors.lastname: Nieschlag
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D020022:Genetic Predisposition to Disease / Q000235:genetics; D005820:Genetic Testing / Q000379:methods*; D006801:Humans; D007248:Infertility, Male / Q000175:diagnosis* / Q000235:genetics / Q000628:therapy*; D007713:Klinefelter Syndrome / Q000175:diagnosis* / Q000235:genetics / Q000628:therapy*; D008297:Male