Klinefelter syndrome is a genetic condition that results when a boy is born with an extra copy of the X chromosome. Klinefelter syndrome is a common genetic condition affecting males, and it often isn't diagnosed until adulthood.
Klinefelter syndrome may adversely affect testicular growth, resulting in smaller than normal testicles, which can lead to lower production of testosterone. The syndrome may also cause reduced muscle mass, reduced body and facial hair, and enlarged breast tissue. The effects of Klinefelter syndrome vary, and not everyone has the same signs and symptoms.
Most men with Klinefelter syndrome produce little or no sperm, but assisted reproductive procedures may make it possible for some men with Klinefelter syndrome to father children.
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
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.
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.
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.
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