Klinefelter Syndrome (XXY): Causes, Signs and Treatment

What it is

Klinefelter syndrome (KS) is a genetic condition in which a male is born with an extra X chromosome. It can affect physical, language and social development and usually causes infertility.

Cause

KS is not inherited. It comes from a random error when a sperm or egg forms.

• Chromosomes are tiny packages in your cells that hold your genes, the DNA that shapes how you look and how your body works. People usually have 46 chromosomes in each cell, two of them sex chromosomes: usually XX in females and XY in males.
• In KS, a male usually has XXY.
• Mosaic KS: rarely, some cells are XY and others XXY. Symptoms may be milder, depending on how many XY cells there are and where.

Signs and symptoms

Some males have no or very mild symptoms and may not know they have KS or be diagnosed right away; others have more severe symptoms.

• In boyhood: often taller than peers, with more fat around the belly; possible learning or language problems, which can make them shy and quiet and have trouble fitting in.
• After puberty, often from low testosterone (the main male sex hormone):
• • smaller testes and penis;
  • breast growth (gynecomastia);
  • less facial and body hair;
  • reduced muscle tone;
  • narrower shoulders and wider hips;
  • weaker bones;
  • lower sex drive and energy.
• Fertility: most males with KS make little or no sperm.

Diagnosis and treatment

• Diagnosis: a karyotype test, which examines a person's chromosomes.
• No cure, but treatment helps — the sooner the better; starting by early puberty is likely to ease symptoms:
• • testosterone replacement;
  • surgery to remove or reduce breast tissue;
  • physical, speech, behavioral and occupational therapy;
  • in some cases, fertility treatment can help men with KS father children.

Sources

Based on "Klinefelter Syndrome," MedlinePlus, U.S. National Library of Medicine, drawing on the NIH National Institute of Child Health and Human Development; a work of the United States government in the public domain.