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Updated: Dec 24 2021

Klinefelter Syndrome

  • Snapshot
    • A 27-year-old man presents to the physician with his wife after a referral from a fertility clinic appointment. The couple has been trying to have a baby without success for the past year. The man is tall and lean in stature. On physical examination, the man has sparse, thin hair in the axilla and pubic areas, small, firm testes, and the finding seen in the image. Analysis of his sperm reveals azoospermia.
  • Introduction
    • Overview
      • Klinefelter syndrome is a sex chromosome disorder that is a common underlying cause of hypogonadism in men
  • Epidemiology
    • Incidence
      • 1-2.5 per 1000 men
        • only 25-50% of Klinefelter syndrome patients are diagnosed during their lifetimes
    • Risk factors
      • advanced maternal age
    • Pathophysiology
      • pathophysiology
        • male child is born with an extra, inactivated X chromosome
          • karyotype 47,XXY
          • nondisjunction during cell division prevents X chromosome from being distributed normally
        • dysgenesis of seminiferous tubules
          • results in primary testicular failure with ↓ androgen production
  • Presentation
    • Symptoms
      • infertility
      • signs of androgen deficiency
        • gynecomastia
          • breast development at puberty
        • sexual dysfunction
        • osteoporosis
    • Physical exam
      • female hair distribution
      • gynecomastia
      • long extremities
      • tall stature
      • small, firm testes
  • Studies
    • Karyotype
      • karyotype 47,XXY provides a definitive diagnosis
      • generally only recommended in prepubertal or pubertal boys, or men with clinical signs of Klinefelter syndrome who are seeking fertility treatment
    • Serum hormone levels
      • ↑ FSH and LH
      • ↓ testosterone
      • ↑ estradiol
  • Differential
    • Double Y males (47,XYY)
      • key distinguishing factor
        • phenotypically normal with intact fertility
    • Fragile X syndrome
      • key distinguishing factor
        • enlarged testes
    • Marfan syndrome
      • key distinguishing factor
        • intact fertility
  • Treatment
    • Medical
      • androgen (testosterone) replacement therapy
        • indications
          • promote development of normal male secondary sex characteristics
    • Lifestyle
      • speech and behavioral therapy
        • indications
          • improve speech impairments and psychosocial problems
  • Complications
    • ↑ risk of breast cancer
      • incidence
        • up to 50-fold ↑ incidence of male breast cancer compared to the normal population
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