Alternative Names
Klinefelter; XXY syndrome; XXY trisomy; 47,XXY; Klinefelter's Syndrome
Symptoms & Characteristics
Klinefelter syndrome (also known as 47, XXY) is characterized by the presence of an extra X chromosome in the cells of a male's body.
Males affected with this condition typically have low levels of the hormone testosterone beginning during puberty. A lack of this hormone can lead to breast development (called gynecomastia), reduced facial and body hair, and an inability to father children (infertility). Compared with other men, adult males affected with Klinefelter syndrome have an increased risk of developing breast cancer and a chronic inflammatory disease called lupus. Boys affected with Klinefelter syndrome may have learning disabilities and difficulty with speech and language development. They tend to be quiet, sensitive, and unassertive, but personality characteristics vary among males affected with this condition.
Variants of Klinefelter syndrome, which involve more than one extra X chromosome (48, XXXY) or extra copies of both the X and Y chromosomes (48, XXYY) in each cell, tend to have more severe signs and symptoms. These disorders affect male sexual development and are associated with decreased IQ, distinctive facial features, skeletal abnormalities, poor coordination, and severe problems with speech.
Treatment
There is no cure for Klinefelter syndrome or variants of Klinefelter syndrome. However, early diagnosis, routine surveillance and treatment can help to manage some of the symptoms and sometimes prevent related problems.
How Common Is It?
Approximately 1 in 500 to 1 in 1,000 males worldwide are affected with Klinefelter syndrome.
- Females are not affected with Klinefelter syndrome.
Genetics & Inheritance
All of our genes are packaged together on chromosomes. People typically have 46 chromosomes in total, which are grouped into 23 pairs. The first 22 pairs are numbered largest to smallest (1-22) and are called autosomes. The last pair are called the sex chromosomes and determine gender, either XX (female) or XY (male). We typically inherit 23 chromosomes (one of each pair) from our mother (in an egg cell) and the other 23 from father (in a sperm cell).
Klinefelter syndrome is caused by the presence of an extra copy of the X chromosome in every cell of a male's body. The extra copy usually occurs as a result of a random "non-disjunction event" in either the egg or the sperm cell. Non-disjunction occurs when chromosomes in the developing egg or sperm fail to separate during cell division. The result is a sperm or egg cell with either an additional chromosome or one that lacks a chromosome. When this sperm or egg cell combines with one from the opposite sex, the resulting embryo will have cells with an extra chromosome (47) or cells that have a missing chromosome (45). The chance for a "non-disjunction event" to occur in an egg increases with age of the biological mother (maternal age). As a consequence, so does the risk for Klinefelter syndrome.
- Variants of Klinefelter syndrome are caused by several extra copies of the X chromosome or extra copies of both the X and Y chromosomes in all of a male's cells. The signs and symptoms of these conditions typically become more severe as the number of X chromosomes increases.
There are other genetic conditions that have symptoms that overlap with Klinefelter syndrome. A genetic consultation with a trained genetic professional is important for a complete evaluation, accurate diagnosis, as well as discussion of the benefits and limitations of chromosome testing and recurrence risk.
Genetic Testing
Klinefelter syndrome can be diagnosed by a chromosome analysis, which is available through an in person genetic consultation for people who are considered at risk. Use our find a genetic professional directory to locate a trained genetic professional in your area.
Support & More Information
More information can be found at:
Support can be found at: