Symptoms

Signs and symptoms of Klinefelter syndrome vary widely among males with the disorder. Many boys with Klinefelter syndrome show few or only mild signs. The condition may go undiagnosed until adulthood or it may never be diagnosed. For others, the condition has a noticeable effect on growth or appearance.

Signs and symptoms of Klinefelter syndrome also vary by age.

Babies

Signs and symptoms may include:

• Weak muscles
• Slow motor development — taking longer than average to sit up, crawl and walk
• Delay in speaking
• Problems at birth, such as testicles that haven't descended into the scrotum

Boys and teenagers

Signs and symptoms may include:

• Taller than average stature
• Longer legs, shorter torso and broader hips compared with other boys
• Absent, delayed or incomplete puberty
• After puberty, less muscle and less facial and body hair compared with other teens
• Small, firm testicles
• Small penis
• Enlarged breast tissue (gynecomastia)
• Weak bones
• Low energy levels
• Tendency to be shy and sensitive
• Difficulty expressing thoughts and feelings or socializing
• Problems with reading, writing, spelling or math

Men

Signs and symptoms may include:

• Low sperm count or no sperm
• Small testicles and penis
• Low sex drive
• Taller than average height
• Weak bones
• Decreased facial and body hair
• Less muscular compared with other men
• Enlarged breast tissue
• Increased belly fat

When to see a doctor

See a doctor if you or your son has:

• Slow development during infancy or boyhood. Delays in growth and development can be the first sign of a number of conditions that need treatment — including Klinefelter syndrome. Though some variation in physical and mental development is normal, it's best to check with a doctor if you have any concerns.
• Male infertility. Many men with Klinefelter syndrome aren't diagnosed with infertility until they realize they're unable to father a child.