Klinefelter syndrome

Dr Euan Zhang and Radswiki et al.

Klinefelter syndrome (KS) is a chromosomal anomaly, which in most cases is characterized by 47 chromosomes instead of the usual 46.

The estimated incidence is 0.15-0.2% of live births.

  • the testes are normal prior to puberty and small in post pubertal testes; there is absent spermatogenesis
  • the kidneys can be symmetrically enlarged with small 1-8 mm cysts
  • post pubertal gynecomastia
  • sparse facial and axillary hair
  • clinodactyly
  • tall stature
  • narrow shoulders
  • broad hips
  • normal to moderately reduced Leydig cell function
  • increased secretion of follicle-stimulating hormone
  • androgen deficiency
  • normal to slightly decreased verbal intelligence
  • ~80% have 47XXY 
  • ~10% have mosaic 46XY/47XXY
  • ~10% have 48XXYY and other less frequent types

These abnormal divisions occur as sporadic events and are not hereditary.

It is named after Harry Klinefelter who first described the syndrome in 1942.

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Article information

rID: 14995
Section: Syndromes
Synonyms or Alternate Spellings:
  • Klinefelter syndrome (KS)
  • Klinefelter's syndrome

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