Klinefelter syndrome

The Klinefelter syndrome is characterized by supernumerary X chromosomes in male karyotype and belongs to the numerical chromosome aberrations and. It only affects boys.

Approximately 80% of those affected have the karyotype 47, XXY. The other 20% have mosaic forms with karyotypes such as 46, XY / 47, XXY. There is no separation in the formation of the parental germ cell during meiosis, the germ cells have excess X chromosomes.

The differing number of heterosomes will also heterosomal aneuploidy. Investigations have shown that this X chromosome comes about equally often from the father or the mother.

Since the symptoms are usually very weak at first, the syndrome is usually diagnosed only at puberty. The underdeveloped testes produce only small amounts of testosterone, which is why they show a delayed physical development which in some even completely absent.