- Related Topics:
- sex chromosome
- trisomy
- XX syndrome
- X chromosome
Klinefelter syndrome
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What is Klinefelter syndrome?
Klinefelter syndrome is a chromosomal disorder that occurs in males, characterized by the presence of one or more extra X chromosomes. The most common form is XXY, instead of the typical XY.
Identified in 1942 and linked to chromosomal abnormality in 1959, Klinefelter syndrome affects approximately 1 in 500 to 1,000 males. Symptoms include small, firm testes, enlarged breasts (gynecomastia), long limbs, and infertility. Affected individuals often have decreased testosterone levels and may experience social adjustment difficulties, though intelligence is usually normal.
Treatment with androgens can help reduce gynecomastia and improve strength and libido. Life expectancy is generally normal but can be reduced by secondary diseases like cancer.
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What causes Klinefelter syndrome?
Klinefelter syndrome is a chromosomal disorder in males resulting from an unequal sharing of sex chromosomes soon after fertilization. In mosaic Klinefelter syndrome, males have an extra X chromosome, typically with a 47,XXY chromosome composition. Other rare chromosome complements include 48,XXYY, 48,XXXY, 49,XXXYY, and 49,XXXXY. About 1 in 400 male live births demonstrate some form of sex chromosome abnormality. Most aneuploids, or abnormal numbers of chromosomes, arise by nondisjunction, where homologous chromosomes fail to separate during meiosis.
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What are chromosomes, and how many do people usually have?
Chromosomes are microscopic structures within cells that contain hereditary information in the form of genes. They are composed of DNA, RNA, and proteins.
Human cells typically contain 23 pairs of chromosomes, for a total of 46. Twenty-two pairs are autosomes, which control the inheritance of most characteristics. The remaining pair consists of sex chromosomes, which determine sex-linked traits.
Klinefelter syndrome is a chromosomal disorder that affects males. Males with mosaic Klinefelter syndrome have an extra X chromosome, typically with a chromosome composition of 47,XXY.
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How does Klinefelter syndrome affect someone’s physical and mental development?
Klinefelter syndrome, a chromosomal disorder affecting males, arises from an extra X chromosome. The most common form is 47,XXY, but variations like 48,XXYY, 48,XXXY, 49,XXXYY, and 49,XXXXY exist.
Physical effects include small, firm testes, enlarged breasts, and infertility. Affected individuals may have disproportionately long legs and arms. Some may experience diabetes, thyroid issues, and increased cancer risk. While intelligence is typically normal, some individuals may face social adjustment difficulties. Those with certain chromosomal variations can experience intellectual disability.
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What are common signs and symptoms of Klinefelter syndrome?
Klinefelter syndrome, a chromosomal disorder in males, arises from an unequal sharing of sex chromosomes after fertilization. Common signs and symptoms include small, firm testes, breast enlargement (gynecomastia), and disproportionately long legs and arms. Affected individuals often experience decreased serum testosterone.
Men with mosaic Klinefelter syndrome may have fewer symptoms, while those with rare chromosome complements may experience intellectual disability and skeletal anomalies. Androgen treatment can reduce gynecomastia and increase strength and libido. Although those affected are typically of normal intelligence, they may experience difficulty with social adjustments.
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How is Klinefelter syndrome diagnosed and treated?
Klinefelter syndrome (47,XXY) is a genetic condition in males associated with infertility, tall stature, and sometimes gynecomastia (partial breast development).
Diagnosis is achieved through karyotyping, a genetic test that analyzes chromosomes to identify abnormalities such as the extra X chromosome present in Klinefelter syndrome.
Treatment with androgens can help reduce gynecomastia and symptoms of male hypogonadism, as well as increase strength and libido. With treatment, many individuals with Klinefelter syndrome have a normal or slightly reduced life expectancy.
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Klinefelter syndrome, disorder of the human sex chromosomes that occurs in males. Klinefelter syndrome is one of the most frequent chromosomal disorders in males, occurring in approximately 1 in every 500 to 1,000 males. It results from an unequal sharing of sex chromosomes very soon after fertilization, with one cell of a dividing pair receiving two X chromosomes and a Y chromosome and the other cell of the pair receiving only a Y chromosome and usually dying. (The normal male chromosome number and sex chromosome composition is 46,XY. )
Klinefelter syndrome is named for Harry Klinefelter, an American physician who in 1942 described a set of symptoms that characterized the condition. The syndrome was first identified with a specific chromosomal abnormality in 1959 by British researcher Patricia A. Jacobs and her colleagues.
Symptoms
Men with Klinefelter syndrome have small, firm testes, and they often have breast enlargement (gynecomastia) and inordinately long legs and arms (eunuchoidism) and are infertile. Affected men have decreased serum testosterone concentrations, with urinary excretion of 17-ketosteroids (components of certain male hormones, or androgens) in the normal or low-normal range. They also have increased serum follicle-stimulating hormone and luteinizing hormone concentrations. Diabetes mellitus, goitre (enlargement of the thyroid gland), and various cancers may be more prevalent among Klinefelter syndrome patients. Thyroidal trapping of radioactive iodine and the responses of the thyroid to injections of thyrotropin (thyroid-stimulating hormone; TSH) may be low. Although normal in intelligence, some affected men have difficulties making social adjustments.
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Chromosome compositions
Sex chromosome composition can vary in those affected by Klinefelter syndrome. With mosaic Klinefelter syndrome (in which tissues are made up of genetically different cells), males have an extra X chromosome, typically with a chromosome composition of 47,XXY. Men with this form of the disorder usually have fewer symptoms than do men with the other chromosomal arrangements associated with Klinefelter syndrome. Other, rare chromosome complements that give rise to mosaic Klinefelter syndrome include 48,XXYY, 48,XXXY, 49,XXXYY, and 49,XXXXY. Men with these chromosome complements suffer from a variety of additional abnormalities, and, unlike men with 47,XXY Klinefelter syndrome, they often suffer from intellectual disability. One variant of the disorder in particular, the 49,XXXXY type, is characterized by fusion of the forearm bones and other skeletal anomalies, underdevelopment of the penis and scrotum, incomplete descent of the testes, and marked intellectual disability. Although about 40 percent of men affected by Klinefelter syndrome have a normal XY pattern, others possess a chromosome variant known as XX syndrome, in which Y chromosome material is transferred to an X chromosome or a nonsex chromosome (autosome). Men with XX syndrome have a male phenotype (physical appearance), but they have changes typical of Klinefelter syndrome.
Treatment
Treatment with androgens reduces gynecomastia and evidence of male hypogonadism and increases strength and libido in patients with all variants of Klinefelter syndrome. In a few of these individuals, sperm obtained from the testes have successfully fertilized oocytes in vitro.
Life expectancy is normal or very slightly reduced for many individuals with Klinefelter syndrome; patients who develop secondary diseases, such as cancer, may have shorter life expectancies.