Symptoms and causes

Symptoms

Signs and symptoms of Klinefelter syndrome vary widely among males with the disorder. Many boys with Klinefelter syndrome have few noticeable signs, and the condition may go undiagnosed until adulthood. 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
  • Quiet, docile personality
  • 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

  • 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 than normal
  • 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.

Causes

Klinefelter syndrome occurs as a result of a random error that causes a male to be born with an extra sex chromosome. It isn't an inherited condition.

Humans have 46 chromosomes, including two sex chromosomes that determine a person's sex. Females have two X sex chromosomes (XX). Males have an X and a Y sex chromosome (XY).

Klinefelter syndrome can be caused by:

  • One extra copy of the X chromosome in each cell (XXY), the most common cause
  • An extra X chromosome in some of the cells (mosaic Klinefelter syndrome), with fewer symptoms
  • More than one extra copy of the X chromosome, which is rare and results in a severe form

Extra copies of genes on the X chromosome can interfere with male sexual development and fertility.

Risk factors

Klinefelter syndrome stems from a random genetic event. The risk of Klinefelter syndrome isn't increased by anything a parent does or doesn't do. For older mothers, the risk is higher but only slightly.

Complications

Klinefelter syndrome may increase the risk of:

  • Anxiety and depression
  • Infertility and problems with sexual function
  • Weak bones (osteoporosis)
  • Heart and blood vessel disease
  • Breast cancer and certain other cancers
  • Lung disease
  • Endocrine conditions such as diabetes and hypothyroidism
  • Autoimmune disorders such as lupus and rheumatoid arthritis
  • Tooth problems that make dental cavities more likely

A number of complications caused by Klinefelter syndrome are related to low testosterone (hypogonadism). Testosterone replacement therapy reduces the risk of certain health problems, especially when therapy is started at the beginning of puberty.