Klinefelter Syndrome: Symptoms & Signs

Medically Reviewed on 10/15/2019

Klinefelter syndrome is a genetic condition in which males (who normally have one X chromosome and one Y chromosome) possess an extra X chromosome (XXY karyotype).

About 1 out of every 500 men have an extra X chromosome, but not all men have symptoms and signs. When signs and symptoms do occur, Klinefelter syndrome is associated with

  • a taller, less muscular body,
  • less facial and body hair, and
  • broader hips than other boys.

Other associated Klinefelter syndrome signs and symptoms can include

  • breast enlargement in men,
  • delayed puberty,
  • flaccid muscles,
  • infertility,
  • low-set ears,
  • osteoporosis,
  • low energy level,
  • reduced sex drive, and
  • a small penis.

Cause of Klinefelter syndrome

The condition is not inherited, rather it is caused by a random error that results in a male being born with an extra X chromosome.

Other klinefelter syndrome symptoms and signs

  • Breast Enlargement in Men
  • Broader Hips Than Other Boys
  • Delayed Puberty
  • Flaccid Muscles
  • Infertility
  • Less Facial and Body Hair
  • Low Energy Level
  • Low-Set Ears
  • Osteoporosis
  • Reduced Sex Drive
  • Small Penis
  • Taller, Less Muscular Body


Jameson, J. Larry, et al. Harrison's Principles of Internal Medicine, 20th Ed. New York: McGraw-Hill Education, 2018.