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. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. Klinefelter syndrome. From Genetics Home Reference.
Description Klinefelter syndrome is a chromosomal condition in boys and men that can affect physical and intellectual development. Frequency Klinefelter syndrome affects about 1 in newborn boys.
Causes Klinefelter syndrome is a sex chromosome disorder in boys and men that results from the presence of an extra X chromosome in cells.
Learn more about the chromosome associated with Klinefelter syndrome x chromosome. Inheritance 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.
Research Studies from ClinicalTrials. The cognitive phenotype in Klinefelter syndrome: a review of the literature including genetic and hormonal factors. Dev Disabil Res Rev. Adv Pediatr.
Chromosomal variants in klinefelter syndrome. These are named either X or Y. The X chromosome is not a "female" chromosome and is present in everyone. The presence of a Y chromosome denotes male sex. Boys and men with Klinefelter syndrome are still genetically male, and often will not realise they have this extra chromosome, but occasionally it can cause problems that may require treatment. Klinefelter syndrome does not usually cause any obvious symptoms early in childhood, and even the later symptoms may be difficult to spot.
Most boys and men with Klinefelter syndrome will not be significantly affected and can live normal, healthy lives. But men with Klinefelter syndrome are at a slightly increased risk of developing other health problems, including:.
These problems can usually be treated if they do occur and testosterone replacement therapy may help reduce the risk of some of them. This chromosome carries extra copies of genes, which interfere with the development of the testicles and mean they produce less testosterone male sex hormone than usual.
The extra genetic information may either be carried in every cell in the body or it may only affect some cells known as mosaic Klinefelter syndrome.
They may have trouble paying attention. A lot of boys learn to talk late or have trouble using words to express their emotions. They also can have trouble with things like learning to spell, read, and write. Socially, they tend to have quiet personalities. They rarely cause trouble and are often more helpful and thoughtful than other boys. They're often shy and sensitive, and many are less self-confident and less active than other boys their age.
Most boys aren't likely to have major health problems, but the condition can bring some other challenges later in life. Klinefelter syndrome puts males at greater risk of breast cancer, some other cancers , and some other diseases like type 2 diabetes, varicose veins and problems with blood vessels, problems with sexual function, and osteoporosis weak bones later in life. Most boys with Klinefelter syndrome can have sex when they become men, usually with the help of testosterone treatment.
But problems with their testicles prevent them from making enough normal sperm to father children. 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. But, as men, most have normal friendships and relationships. Most teens with Klinefelter syndrome aren't likely to have major health problems. But the condition can bring challenges later in life.
For example, guys with Klinefelter syndrome may be more likely to get some types of cancer and other diseases, like type 2 diabetes and osteoporosis, a condition where the bones become weaker later in life.
As men, most guys with Klinefelter syndrome can have sex, usually with the help of testosterone treatment. But problems with their testicles prevent them from making enough normal sperm to father children. Fertility researchers are working on new treatments. By the time a teen with Klinefelter syndrome is ready to become a dad, there may be new options available related to the extraction of sperm from the testicles. The earlier a guy finds out about Klinefelter syndrome, the better. Treatments are most effective if they start while a guy is still young.
So if you're worried about your development, talk to your doctor. It might be nothing, but it's always best to know, especially because Klinefelter syndrome can be hard to notice. To diagnose a guy with Klinefelter syndrome, doctors usually begin by asking about any learning or behavior issues and examining the testicles and body proportions.
They'll check a blood sample for the presence of the extra X chromosome. Doctors also can do hormone testing, usually by taking a blood sample to check for abnormal hormone levels. There's no way to change the XXY condition if someone is born with it, but there are treatments that can help.
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