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.
Klinefelter syndrome is not directly inherited — the additional X chromosome occurs as a result of either the mother's egg or the father's sperm having the extra X chromosome an equal chance of this happening in either , so after conception the chromosome pattern is XXY rather than XY.
Other Names:. Congenital and Genetic Diseases. This disease is grouped under:. Summary Summary. Symptoms Symptoms. The signs and symptoms of Klinefelter syndrome KS vary among affected people. Some men with KS have no symptoms of the condition or are only mildy affected. In these cases, they may not even know that they are affected by KS. In these cases, known as "variants of Klinefelter syndrome", the signs and symptoms can be more severe and may include: [1] [2] [4] Intellectual disability Distinctive facial features Skeletal abnormalities Poor coordination Severe speech difficulties Behavioral problems Heart defects Teeth problems.
Cause Cause. Klinefelter syndrome usually occurs as a random event during the formation of reproductive cells eggs and sperm. An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes. For example, an egg or sperm cell may gain one or more extra copies of the X chromosome as a result of nondisjunction. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have one or more extra X chromosomes in each of the body's cells.
Some people with Klinefelter syndrome have the extra X chromosome in only some of their cells; these people are said to have mosaic Klinefelter syndrome. Women who have pregnancies after age 35 have a slightly increased chance of having offspring with this syndrome. Inheritance Inheritance. Klinefelter syndrome is not inherited , but usually occurs as a random event during the formation of reproductive cells eggs and sperm.
An error in cell division called nondisjunction can result in reproductive cells with an abnormal number of chromosomes. If one of these reproductive cells contributes to the genetic makeup of a child, the child will have one or several extra X chromosomes in each of the body's cells. Diagnosis Diagnosis. A diagnosis of Klinefelter syndrome is often suspected based on the presence of characteristic signs and symptoms.
Additional testing can then be ordered to confirm the diagnosis. This generally includes a chromosomal analysis called a karyotype. Treatment Treatment. Because symptoms of Klinefelter syndrome KS can sometimes be very mild, many people are never diagnosed or treated. When a diagnosis is made, treatment is based on the signs and symptoms present in each person, especially the problems related to hypogonadism , gynecomastia , and psychosocial problems.
Treatment may include: [1] [3] [4] Testosterone replacement: About half of people with SK have low testosterone levels, which may be raised by taking supplemental testosterone.
Having a more normal testosterone level can help affected people develop bigger muscles, a deeper voice, and facial and body hair, and may also increase sexual desire, enlarge the testes , improve mood, self-image, and behavior; it may also protect against osteoporosis and decrease the risks of autoimmune disease and breast cancer.
Breast removal or reduction surgery. Educational interventions: As children, many people with Klinefelter syndrome qualify for special services to help them in school. 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. 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. 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. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission.
This content does not have an English version. This content does not have an Arabic version. Some affected individuals also have differences in their genitalia, including undescended testes cryptorchidism , the opening of the urethra on the underside of the penis hypospadias , or an unusually small penis micropenis.
Other physical changes associated with Klinefelter syndrome are usually subtle. Older children and adults with the condition tend to be somewhat taller than their peers. Other differences can include abnormal fusion of certain bones in the forearm radioulnar synostosis , curved pinky fingers fifth finger clinodactyly , and flat feet pes planus. Children with Klinefelter syndrome may have low muscle tone hypotonia and problems with coordination that may delay the development of motor skills, such as sitting, standing, and walking.
Affected boys often have learning disabilities, resulting in mild delays in speech and language development and problems with reading.
Boys and men with Klinefelter syndrome tend to have better receptive language skills the ability to understand speech than expressive language skills vocabulary and the production of speech and may have difficulty communicating and expressing themselves.
About 10 percent of boys and men with Klinefelter syndrome have autism spectrum disorder. Nearly half of all men with Klinefelter syndrome develop metabolic syndrome, which is a group of conditions that include type 2 diabetes , high blood pressure hypertension , increased belly fat, high levels of fats lipids such as cholesterol and triglycerides in the blood. Compared with unaffected men, adults with Klinefelter syndrome also have an increased risk of developing involuntary trembling tremors , breast cancer if gynecomastia develops , thinning and weakening of the bones osteoporosis , and autoimmune disorders such as systemic lupus erythematosus and rheumatoid arthritis.
Autoimmune disorders are a large group of conditions that occur when the immune system attacks the body's own tissues and organs. Klinefelter syndrome affects about 1 in newborn boys. It is among the most common sex chromosome disorders, which are conditions caused by changes in the number of sex chromosomes the X chromosome and the Y chromosome.
Klinefelter syndrome is a sex chromosome disorder in boys and men that results from the presence of an extra X chromosome in cells. People typically have 46 chromosomes in each cell, two of which are the sex chromosomes. Most often, boys and men with Klinefelter syndrome have the usual X and Y chromosomes, plus one extra X chromosome, for a total of 47 chromosomes 47,XXY. 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.
0コメント