Klinefelter Syndrome Home A-Z Health Information Health Library A-Z Klinefelter Syndrome Overview Klinefelter syndrome is a genetic condition in males caused by an extra X chromosome. Many men with Klinefelter syndrome are not diagnosed with infertility until they realise they are unable to father a child. Symptoms Reduced muscle mass, enlarged breast tissue, infertility, and learning difficulties. Diagnosis Genetic testing and evaluating physical and developmental symptoms. Treatment Testosterone replacement therapy to address hormonal deficiencies, physical therapy to improve muscle strength, speech and educational support, and fertility treatments if desired. Early diagnosis and intervention are important to address developmental and health challenges, enabling individuals with Klinefelter syndrome to lead healthy and productive lives. Disclaimer: The information in this Health Library is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional with any questions about a medical condition or before starting any treatment. Use of this site and its content does not establish a doctor–patient relationship. In case of a medical emergency, call your local emergency number or visit the nearest emergency facility immediately.