Genetics Home > Genetic Cause of Klinefelter Syndrome
The genetic cause of Klinefelter syndrome is the presence of an extra X chromosome in each cell. Scientists studying Klinefelter syndrome are not sure what the risk factors are for having a child that carries the extra chromosome.
The cause of Klinefelter syndrome is one (or more) extra sex chromosome in each cell.
While Klinefelter syndrome is genetic (in that it involves an extra X chromosome), it is not usually hereditary in the conventional sense. That is, Klinefelter syndrome is not inherited, nor does it "run in families." Klinefelter syndrome is usually the result of a random event that occurs during the formation of reproductive cells (eggs and sperm).
Chromosomes, the spaghetti-like strands of hereditary material found in each cell of the body, determine such characteristics as the color of our eyes and hair, our height, and whether we are male or female.
In humans, there are 23 pairs of chromosomes in the cells: one pair is inherited from each parent. Each cell contains 22 pairs of chromosomes, called autosomes, that are the same in males and females. The remaining pair of chromosomes, the X and Y chromosomes, are not shaped similarly, and thus are not matched in the same way as the autosomes.
The X and Y chromosomes are called sex chromosomes. They are responsible for the difference in development between males and females. A Y chromosome contains genes responsible for testes development, and the presence of an X chromosome paired with a Y chromosome will determine male development. On the other hand, two X chromosomes are required for normal ovarian development in females.