Klinefelter 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
- Genetics Home Reference: Klinefelter syndrome (National Library of Medicine)
- How Do Health Care Providers Diagnose Klinefelter Syndrome? (National Institute of Child Health and Human Development)
- Karyotyping Available in Spanish
- Klinefelter Syndrome (Genetic and Rare Diseases Information Center)
- Klinefelter Syndrome (Mayo Foundation for Medical Education and Research)
- Klinefelter Syndrome (For Teens) (Nemours Foundation)
- Klinefelter Syndrome (KS): Condition Information (National Institute of Child Health and Human Development)
- Klinefelter Syndrome (KS): Other FAQs (National Institute of Child Health and Human Development)
- Learning about Klinefelter Syndrome (National Human Genome Research Institute)
- What Are Common Symptoms of Klinefelter Syndrome? (National Institute of Child Health and Human Development)
- What Are the Treatments for Symptoms in Klinefelter Syndrome? (National Institute of Child Health and Human Development)
- ClinicalTrials.gov: Klinefelter Syndrome (National Institutes of Health)