Klinefelter syndrome (KS) is a disorder that occurs in some men who have more than one X chromosome (XXY). Virtually every cell in the body contains chromosomes, which carry the genes that determine many of our physical, intellectual, and emotional characteristics.
Males usually inherit a single X chromosome from their mother and a single Y chromosome from their father. Males with KS get at least one extra X chromosome from either their mother or their father. In most cases, there is only one extra chromosome.
The extra X chromosome is caused by a biological accident. Normally, an egg has one X chromosome and a sperm has one X or one Y chromosome. Occasionally, an egg may end up with two X chromosomes or a sperm may have both an X and a Y chromosome. When these abnormal eggs are fertilized by a normal sperm, or the abnormal sperm fertilizes a normal egg, the result is a male with two X chromosomes and one Y chromosome (XXY).
A risk factor is something that increases your chance of getting a disease or condition. Women over age 35 have a slightly increased chance of having a child with KS. There are no other known risk factors for this disorder.
Although the chromosome variation XXY occurs in approximately 1 out of 1,000 live male births, many men with it do not develop KS.
When KS does develop, it usually goes undetected until puberty and sometimes much later. It may present during fetal development as an unexpected finding on an
amniocentesis
, in childhood as learning problems, in adolescence as excessive breast development, or in adult life as infertility concerns. Babies born with KS often have a smaller birth weight and slower muscle and motor development. Characteristics may include:
- Tallness with extra long arms and legs
- Abnormal body proportions (long legs, short trunk)
- Enlarged breasts
- Lack of facial and body hair
- Small firm testes
- Small penis
- Lack of ability to produce sperm
- Diminished sex drive
- Sexual dysfunction
- Learning disabilities
- Personality impairment
The most common findings in males with Klinefelter syndrome are sterility, breast development, incomplete masculine body, and social and/or school learning problems.
Although their IQ is normal to borderline, most people with KS also have problems with speech and language. They often learn to speak later than other children do, and learning to read and write may be challenging. Eventually, individuals with KS learn to speak normally but continue to have some difficulty with language throughout their lives. If these difficulties are not treated, social and/or school learning problems arise.
Individuals with KS also have an increased risk of:
Diagnosis of the XXY chromosome variation is made with a test called a karyotype, which examines all 23 pairs of chromosomes. In the case of KS, there are usually 47 chromosomes rather than the normal 46.
Many men with XXY live their whole lives without knowing they have an extra chromosome. If they do get diagnosed, it is most likely at one of the following times:
- Before birth, if amniocentesis or chorionic villus sampling (CVS) is done—These tests may be done if there is a family history of genetic problems, the pregnant woman is over age 35, or there are other medical concerns.
-
Babies or toddlers with
undescended testicles
or a very small penis
- Early childhood, when a boy has trouble learning to talk, read, and write
- Teenage years, if the breasts grow more than usual and puberty fails to develop normally in other ways
- Adulthood, during testing for infertility
Treatment of KS includes:
The main treatment is testosterone. When boys with KS are 10-12 years old, their hormone levels are checked yearly. If their testosterone levels are low, then treatment with testosterone may be helpful. Men diagnosed in adulthood may also benefit from taking the hormone, as well. However, testosterone cannot reverse infertility.
Testosterone is most often given through regular shots in the form of depotestosterone. The benefits of this treatment include:
- Increased strength
- More muscular, male appearance
- Growth of facial and body hair
- Better self-esteem
- Modulation of mood
- Increased energy
- Increased ability to concentrate
- Greater sex drive
Treatment of speech and language difficulties should begin in early childhood to avoid social and school learning problems. Treatment may involve:
- Speech therapy
- Special education services
- Extra support and help with learning from parents and teachers
- Social skills training and psychological counseling to cope with any negative effects of the speech and language problems
Currently, there are no known ways of preventing KS.
