Klinefelter's syndrome (KS) is a condition that occurs in men who have an extra X chromosome. The syndrome can affect different stages of physical, language, and social development.

The most common symptom is infertility. Boys may be taller than other boys their age, with more fat around the belly. After puberty, KS boys may have

• Smaller testes and penis
• Breast growth
• Less facial and body hair
• Reduced muscle tone
• Narrower shoulders and wider hips
• Weaker bones
• Decreased sexual interest
• Lower energy

KS males may have learning or language problems. They may be quiet and shy and have trouble fitting in.

A genetic test can diagnose KS. There is no cure, but treatments are available. It is important to start treatment as early as possible. With treatment, most boys grow up to have normal lives.

Treatments include testosterone replacement therapy and breast reduction surgery. If needed, physical, speech, language, and occupational therapy may also help.

NIH: National Institute of Child Health and Human Development