Klinefelter Syndrome — Basic Genetics: Introduction to the Chromosomal Condition 47, XXY

The typical human has 23 pairs of chromosomes in each of their somatic (body) cells. Among them are the sex chromosomes, X and Y. Males usually have one X and one Y, whereas females have two Xs. Males with Klinefelter syndrome have an extra X, hence the condition sometimes being referred to as XXY syndrome.

Only males are affected by Klinefelter syndrome, and symptoms are caused by the expression of extra X chromosome genes. Signs of the syndrome include:

  • Learning disabilities
  • Breast enlargement
  • Infertility

Signs and symptoms vary from one individual to another. Treatment is focused on reducing or managing symptoms, as there is currently no way of reversing the genetic abnormality.

Klinefelter Syndrome — Chromosome Abnormality

A male with Klinefelter syndrome will have an extra X chromosome in all of his somatic cells, giving him 47 chromosomes instead of 46. Rarely, males can have even more sex chromosomes, for example XXYY or XXXXY. Such conditions are sometimes considered to be variations of Klinefelter syndrome.

Sometimes males have extra X chromosomes only in some somatic cells. This is referred to as mosaic Klinefelter syndrome. Males with this abnormality can also experience symptoms of Klinefelter syndrome. These symptoms are usually milder, for example, a male with mosaic Klinefelter syndrome is more likely to be fertile.

Is Klinefelter Syndrome Inherited?

Klinefelter syndrome is not passed down through generations. The extra X is the result of a random cell division error called nondisjunction. When the chromosomes are being copied to make sex cells, they don’t separate properly, resulting in extra material in a sperm or egg.

Genetic Testing for Klinefelter Syndrome

Klinefelter syndrome can be detected with a karyotype, a picture of a person’s chromosomes used to spot abnormalities in number or structure. An individual with Klinefelter syndrome symptoms may also undergo other investigations associated with the condition, such as fertility testing. Genetic counselors are the professionals who can inform people about genetic testing.

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