Klinefelter syndrome is caused by the presence of one or more extra X chromosomes in a male's cells.
While typical males have one X and one Y chromosome (XY), individuals with Klinefelter syndrome usually have an XXY chromosomal makeup. This extra X chromosome disrupts normal male sexual development. The most common karyotype is 47,XXY, but rarer variants such as 48,XXXY, 48,XXYY, and 49,XXXXY can also occur. These rarer variants generally present with more severe symptoms.
Here's a breakdown:
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The Core Issue: The fundamental cause is an aneuploidy, meaning there's an abnormal number of chromosomes. In this case, it's a sex chromosome aneuploidy.
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Extra X Chromosome's Effect: The extra X chromosome carries extra copies of genes. These extra genes interfere with the development of the testicles, often leading to reduced testosterone production.
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Chromosomal Variations: While XXY is the most common, the syndrome's severity and specific symptoms can vary depending on the number of extra X chromosomes and the presence of mosaicism (where some cells have a normal XY karyotype, while others have XXY or other variations).
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Not Inherited: Klinefelter syndrome is usually not inherited. It's a random genetic event that occurs during the formation of egg or sperm cells (meiosis) or early in embryonic development.
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Testosterone Deficiency: A major consequence of the chromosomal abnormality is the potential for hypogonadism (reduced function of the testes), which can result in lower testosterone levels. This can lead to various physical and developmental characteristics associated with Klinefelter syndrome.
