Heredity of Turner Syndrome
Because Turner syndrome is a genetic disorder, many people have questions about the heredity of Turner syndrome. Most cases are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). Turner syndrome is not usually hereditary in the conventional sense, meaning that it does not typically "run in families."
Heredity of Turner Syndrome: An Overview
While Turner syndrome is genetic in that it involves the complete or partial absence of X chromosome genes (see Cause of Turner Syndrome), it is not usually hereditary in the conventional sense. That is, it does not typically "run in families."
The one exception to this observation is families with an X chromosome deletion, which is stable enough to be passed down through the generations and which also allows fertility.
Random Events Cause Turner Syndrome
Most cases of Turner syndrome are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). An error in cell division called nondisjunction can result in reproductive cells with an abnormal number of chromosomes. For example, an egg or sperm cell may lose a sex chromosome as a result of nondisjunction. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have a single X chromosome in each cell and will be missing the other sex chromosome.
Heredity of Mosaic Turner Syndrome
Mosaic Turner syndrome is also not inherited. It occurs as a random error during cell division in early fetal development. As a result, some of an affected person's cells have the usual two sex chromosomes (either two X chromosomes, or one X chromosome and one Y chromosome), and other cells have only one copy of the X chromosome.