Clinical features: The diagnosis of Klinefelter syndrome is usually made in adulthood during the investigation of infertility, although some of the clinical features of the condition may make a diagnosis possible. These features include: poorly developed secondary sexual characteristics (sparse pubic, armpit, and facial hair), underdevelopment of the testicles (hypogonadism), which usually leads to infertility, and enlarged breasts (gynaecomastia). Men with Klinefelter syndrome are usually above average height, but have altered body proportions with long limbs and short trunk. Testosterone replacement therapy from early adolescence may assist the development of secondary sexual characteristics and may also help to prevent osteoporosis. Although infertility is usual, a few men with Klinefelter syndrome have fathered children following assisted reproduction by intracytoplasmic sperm injection (ICSI) and expert advice regarding this should be sought when appropriate.
Incidence: The overall birth incidence is 1 in 1,000 males, with a maternal age effect. The frequency is 100/1000 in infertile males, Klinefelter syndrome being the commonest cause of hypogonadism and infertility in men.
Chromosome result: 47,XXY; mosaicism in approximately 15%.
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