Signs and symptoms of Klinefelter syndrome vary by age and vary widely between individuals.
In infants, 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 have not descended into the scrotum
In 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
- A tendency to be shy and sensitive
- Difficulty expressing thoughts and feelings or socializing
- Problems with reading, writing, spelling or math
In adult males, 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