NHGRI is part of the National Institutes of Health and supports research on the structure and function of the human genome and its role in health and disease. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.
In-Depth Information Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free. The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers.
This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition. Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge. PubMed is a searchable database of medical literature and lists journal articles that discuss Klinefelter syndrome.
Click on the link to view a sample search on this topic. Have a question? References References. Klinefelter syndrome. Genetics Home Reference. Kirmse B. Chen H. Medscape Reference. Learning about Klinefelter syndrome. National Human Genome Research Institute. Klinefelter Syndrome. National Organization for Rare Disorders. Do you know of a review article? Share this content:. Close Copy Link. You May Be Interested In.
How to Find a Disease Specialist. Tips for the Undiagnosed. Support for Patients and Families. Tips for Finding Financial Aid. Help with Travel Costs. Boys and men with Klinefelter syndrome have an extra copy of multiple genes on the X chromosome.
The activity of these extra genes may disrupt many aspects of development, including sexual development before birth and at puberty, and are responsible for the common signs and symptoms of Klinefelter syndrome. Researchers are working to determine which genes contribute to the specific developmental and physical differences that can occur with Klinefelter syndrome. Some people with features of Klinefelter syndrome have an extra X chromosome in only some of their cells; other cells typically have one X and one Y chromosome.
Rarely, other cells may have additional chromosome abnormalities. It is thought that less than 10 percent of individuals with Klinefelter syndrome have the mosaic form.
Boys and men with mosaic Klinefelter syndrome may have milder signs and symptoms than those with the extra X chromosome in all of their cells, depending on what proportion of cells have the additional chromosome. Several conditions resulting from the presence of more than one extra sex chromosome in each cell are sometimes described as variants of Klinefelter syndrome.
Like Klinefelter syndrome, these conditions affect male sexual development and can be associated with learning disabilities and problems with speech and language development. However, the features of these disorders tend to be more severe than those of Klinefelter syndrome and affect more parts of the body.
As doctors and researchers have learned more about the differences between these sex chromosome disorders, they have started to consider them as separate conditions. Klinefelter syndrome is not inherited; the addition of an extra X chromosome occurs during the formation of reproductive cells eggs or sperm in one of an affected person's parents. During cell division , an error called nondisjunction prevents X chromosomes from being distributed normally among reproductive cells as they form.
Typically, as cells divide, each egg cell gets a single X chromosome, and each sperm cell gets either an X chromosome or a Y chromosome. However, because of nondisjunction, an egg cell or a sperm cell can also end up with an extra copy of the X chromosome. If an egg cell with an extra X chromosome XX is fertilized by a sperm cell with one Y chromosome, the resulting child will have Klinefelter syndrome. Similarly, if a sperm cell with both an X chromosome and a Y chromosome XY fertilizes an egg cell with a single X chromosome, the resulting child will have Klinefelter syndrome.
It occurs as a random error during cell division early in fetal development. As a result, some of the body's cells have the usual one X chromosome and one Y chromosome 46,XY , and other cells have an extra copy of the X chromosome 47,XXY. Genetics Home Reference has merged with MedlinePlus. Learn more. A therapist or counselor can help you manage any depression, low self-esteem, or other emotional issues that stem from this condition.
You might also look for a support group, where you can talk with other men who have this condition. You can find support groups through your doctor or on the internet. Children with Klinefelter syndrome often need extra help in school.
Contact your local school district to find out about special programs for kids with disabilities. Many boys with Klinefelter syndrome have more trouble interacting socially than their peers.
An occupational or behavioral therapist can help them learn social skills. You and your doctor will need to watch out for conditions that are more common in men with Klinefelter syndrome, including:. According to research , Klinefelter syndrome can shorten your life expectancy up to two years.
However, you can still live a long, full life with this condition. The earlier you get treatment, the better your outlook will be. Mosaic Down syndrome is a rare, less severe form of Down syndrome. We explain the condition, its cause, symptoms, and how to diagnose it. Down syndrome is the most common genetic condition in the United States. Curly hair is determined by factors you inherit from your biological parents. Here's how it works.
Health Conditions Discover Plan Connect. What are the symptoms? Most men with the condition are infertile and can't father a child the usual way. Options for becoming natural parents are limited, but fertility researchers are working on new treatments. By the time someone with Klinefelter syndrome is ready to become a dad, there may be new options available related to saving sperm from the testicles.
Since Klinefelter syndrome can be hard to notice, many parents don't know their son has it until he grows up or shows delays in puberty. Sometimes, parents who are worried about their son's development consult a doctor, and the diagnosis reveals Klinefelter syndrome. This can help, because the earlier a boy is diagnosed with Klinefelter syndrome, the more effective the treatments usually are. To diagnose Klinefelter syndrome, doctors usually begin by asking about any learning or behavior issues and examining the boy's testicles and body proportions.
They'll check a blood sample for the extra X chromosome. Before birth, the condition may be found through chromosomal analysis or noninvasive prenatal testing NIPT.
NIPT is done on the fluid surrounding the fetus, tissue from the placenta, or the blood from the mother. After birth, doctors can make a diagnosis with a chromosome karyotype test or microarray test from the baby. Doctors also can do hormone testing, usually by taking a blood sample to check for unusual hormone levels. There's no way to change the XXY condition if a boy is born with it, but treatments can help relieve some symptoms.
As with many conditions, beginning treatment early can make it much more effective. Testosterone replacement therapy TRT works by increasing a boy's testosterone levels into the normal range. Additional testosterone can help a boy with Klinefelter syndrome develop bigger muscles and a deeper voice, as well as promote growth of the penis and facial and body hair.
It can also help improve bone density and reduce the growth of a boy's breasts. Testosterone therapy cannot increase the size of a boy's testicles or prevent or reverse infertility, though.
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