Klinefelter Syndrome

Aka: Klinefelter Syndrome

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II. Epidemiology

  1. Most common major sexual differentiation abnormality
  2. Incidence of Klinefelter Syndrome in specific cohorts
    1. Newborn males: 1 in 500 to 1000
    2. Male Breast Cancer: 7.5%
    3. Infertile males: 3%
    4. Mild Mental Retardation: 1%

III. Pathophysiology

  1. Results in testicular dysgenesis
  2. Chromosomal abnormality with 47,XXY karyotype
    1. Abnormality of nondisjunction during meiosis
    2. Maternal or paternal origin
    3. Most of additional X Chromosome is inactivated
      1. Functioning extra genes confer Phenotype
      2. More severe cases with XXXY, XXXXY or XXYY
      3. Less severe cases with mosaicism (>1 cell line)

IV. Signs

  1. Late Eunuchoid body proportions
    1. Tall, slim and underweight
    2. Long legs and short torso
    3. Obesity and varicosities may occur in 33% of patients
  2. Hypergonadotropic Hypogonadism
    1. Testes small and firm (usually <2.0 cm or 2 ml)
    2. Penis small
    3. Azoospermia or Oligospermia (and Infertility)
  3. Other signs of Hypoandrogenism
    1. Gynecomastia (bilateral and painless)
    2. Decreased facial hair, but pubic hair abundant

V. Labs

  1. Karyotype: XXY
  2. Post-Puberty labs
    1. Follicle Stimulating Hormone (FSH) increased
    2. Leutinizing Hormone (LH) increased
    3. Inhibin B decreased
    4. Increased Estradiol to Testosterone ratio

VI. Associated Conditions

  1. Mild Mental Retardation
    1. Motor function delay
    2. Language comprehension problems
    3. Speech may also be affected
  2. Learning Disorders
    1. Attention Deficit Disorder
    2. Dyslexia
  3. Social maladjustment
  4. Mental illness
  5. Thyroid dysfunction
  6. Diabetes Mellitus
  7. Lung disease
  8. Breast Cancer (20x risk of healthy men)
  9. Osteoporosis

VII. Management: General

  1. Complete neurodevelopment evaluation at diagnosis
    1. Indicated if diagnosis in childhood
  2. Breast Cancer surveillance

VIII. Management: Testosterone Replacement after age 11

  1. Start
    1. Long acting Testosterone 25-50 mg IM q3-4 weeks
    2. Increase Testosterone dose by 50 mg q6-9 months
    3. Goal: 200 to 250 mg q3-4 weeks
  2. Maintenance
    1. Convert to Testosterone patches when at 200-250 mg

IX. Resources

  1. American Association for Klinefelter Syndrome
    1. http://www.aaksis.org
  2. Klinefelter Syndrome Support Group
    1. http://klinefeltersyndrome.org

X. References

  1. Mendoki (1991) J Am Acad Child Adolesc Psychiatry 30 [PubMed]
  2. Schwartz (1991) Endocrinol Metab Clin North Am 20:153 [PubMed]
  3. Smyth (1998) Arch Intern Med 158(12):1309-14 [PubMed]
  4. Behrman (2000) Nelson Pediatrics, Saunders, p. 1746-9
  5. Wattendorf (2005) Am Fam Physician 72:2259-62
  6. Wilson (1991) Harrison's Medicine, McGraw-Hill, p. 1800

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