Men’s Health
Klinefelter Syndrome
This genetic condition can cause infertility or other health issues, but you’re not alone. We offer treatments to help you live your healthiest life.
Medically reviewed by Marc Dall'Era, M.D. on April 06, 2026.
What Is Klinefelter Syndrome?
Klinefelter syndrome affects males who are born with an extra X chromosome. Chromosomes are strings of DNA inside your body’s cells. Your DNA tells every part of your body how to work. Most males have one X and one Y chromosome (XY), but males with Klinefelter syndrome have an extra X chromosome (XXY). This extra chromosome affects how your body develops, particularly your testicles and hormone production.
Klinefelter syndrome occurs in about 1 in 500 male births, making it one of the most common chromosomal conditions. Many men with this condition don't know they have it. Symptoms can be mild or may not appear until puberty or adulthood.
The condition affects testosterone production and can lead to infertility, but with proper treatment, men with Klinefelter syndrome can live healthy, fulfilling lives. UC Davis Health urology experts provide comprehensive care to help you achieve your health and family-building goals.
On this page
Symptoms of Klinefelter Syndrome
The symptoms of Klinefelter syndrome vary from person to person. Some men have no noticeable symptoms, while others have more significant effects.
Physical and Developmental Symptoms
Men with Klinefelter syndrome may have physical changes that become more noticeable during and after puberty. Common physical symptoms include:
- Decreased facial and body hair
- Gynecomastia (Breast tissue development in males)
- Less muscle mass and strength
- Longer arms and legs than typical for body height
- Small, firm testicles (usually less than 2 cm in length)
- Smaller penis size
- Taller than average height (usually over 6 ft)
- Weaker bones or osteoporosis
Learning, Behavioral and Emotional Symptoms
Klinefelter syndrome can affect learning, behavior and emotional well-being. These symptoms may include:
- Anxiety or depression
- Delayed speech or language development
- Dyslexia or learning disabilities
- Low self-esteem
- Poor impulse control
- Problems with attention and focus
- Reduced short-term memory
- Trouble in social situations or with peer relationships
Causes of Klinefelter Syndrome
Klinefelter syndrome is caused by a random error that adds an extra X chromosome in some or all of the body's cells. Men do not inherit the condition from parents and is not caused by anything the parents did or didn't do during pregnancy.
Chromosomal Error in Egg or Sperm
In about half of all cases, the error occurs when the father's sperm is forming. The sperm forms with both an X and a Y chromosome instead of one or the other. In about 40% of cases, the error happens when the mother's egg is forming. The egg forms with two X chromosomes instead of one.
Error After Conception
In about 3% of cases, the chromosomal error occurs after the egg is fertilized, during early cell division. This can result in mosaicism, where some cells have the typical XY pattern and others have XXY.
Diagnosis and Testing for Klinefelter Syndrome
Many men with Klinefelter syndrome get a diagnosis when they seek medical care for infertility or other symptoms as an adult. However, early diagnosis can help with timely treatment. Your doctor may use several methods to diagnose Klinefelter syndrome:
Blood Tests
Blood tests measure hormone levels that may be low in people with Klinefelter syndrome. Doctors can also do chromosomal karyotype testing, which examines your chromosomes using a blood sample.
Prenatal Testing
Klinefelter syndrome can be detected before birth through prenatal testing, such as amniocentesis or chorionic villus sampling.
Semen Analysis
If you are experiencing infertility, your doctor may perform a semen analysis to check for the presence of sperm. Most males with Klinefelter syndrome have azoospermia, meaning no sperm are present in the ejaculate.
Testicular Biopsy
If your doctor suspects you have mosaicism or you are exploring fertility options, they may recommend a testicular biopsy. This procedure removes a small sample of testicular tissue to examine for the presence of sperm-producing cells.
Klinefelter Syndrome Treatments
While there is no cure for Klinefelter syndrome, treatment can manage symptoms and improve your quality of life. At UC Davis Health, we provide personalized and compassionate care tailored to your specific needs and goals.
Behavioral Health and Therapy Services
Many men with Klinefelter syndrome benefit from speech-language pathology, occupational therapy and tutoring for learning disabilities. Counseling or therapy can also help with emotional challenges, social skills and self-esteem.
Bone Health Optimization
Klinefelter syndrome increases the risk of osteoporosis. Your doctor may recommend calcium and vitamin D supplements, weight-bearing exercises and DEXA scans (bone density screenings) to help. Testosterone therapy also helps improve bone strength.
Breast Reduction Surgery
Gynecomastia can cause physical discomfort or emotional distress. Plastic surgery can remove the excess breast tissue.
Fertility Treatment
Our urologists are highly experienced in sperm retrieval surgeries, including microdissection testicular sperm extraction (micro-TESE). This procedure removes sperm from the testicles, which can then be used with in-vitro fertilization (IVF) to help you have biological children.
Testosterone Replacement Therapy
Testosterone replacement therapy helps develop and maintain masculine physical characteristics, increases muscle mass, improves bone density and supports sexual function. Testosterone can be given through injections, patches or gels.
“Klinefelter Syndrome,” JAMA Internal Medicine, https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/207495
“How many people are affected by or at risk for Klinefelter syndrome (KS)?,” NIH, https://www.nichd.nih.gov/health/topics/klinefelter/conditioninfo/risk
Klinefelter syndrome affects
1 in 500Male patients
Source: JAMA Internal Medicine: Klinefelter Syndrome
Request an Appointment
As Sacramento's No. 1 hospital, you'll benefit from unique advantages in primary care and specialty care. This includes prevention, diagnosis and treatment options from experts in 150 specialties.
Referring Physicians
To refer a patient, submit an electronic referral form or call.
Patients
Call to make an appointment.
Consumer Resource Center
Awards and Recognitions
Ranked among the best in 6 specialties
A U.S. News & World Report best hospital in cancer care, cardiology, heart & vascular surgery, geriatrics, neurology & neurosurgery, orthopedics, and pulmonology & lung surgery.
Ranked among the nation’s best children’s hospitals
U.S. News & World Report ranked UC Davis Children’s Hospital among the best in pediatric nephrology, orthopedics*, and pulmonology & lung surgery. (*Together with Shriners Children’s Northern California)
Ranked Sacramento’s #1 hospital
Ranked Sacramento’s #1 hospital by U.S. News, and recognized in 23 types of care including acute kidney failure, cancer care, cardiology, heart & vascular surgery, COPD, colon cancer surgery, diabetes, diabetes & endocrinology, ear, nose & throat surgery, gastroenterology & GI surgery, geriatrics, gynecological cancer surgery, heart arrhythmia, heart attack, heart failure, hip fracture, hip replacement, leukemia, lymphoma & myeloma, lung cancer surgery, neurology & neurosurgery, orthopedics, pneumonia, pulmonology & lung surgery and stroke.
The nation’s highest nursing honor
UC Davis Medical Center has received Magnet® recognition, the nation’s highest honor for nursing excellence.
World-class cancer care
One of ~59 U.S. cancer centers designated “comprehensive” by the National Cancer Institute.
A leader in health care equality
For the 13th consecutive year, UC Davis Medical Center has been recognized as an LGBTQ+ Healthcare Equality Leader by the educational arm of America’s largest civil rights organization.
Latest Urology News
