Occurring in 1 out of 800 live births, Down syndrome is the most frequent genetic cause of mild to moderate mental retardation. While it is genetic in that it involves an extra chromosome 21 (trisomy 21), it is not an inherited condition. Because there is no cure for Down syndrome, treatment involves controlling symptoms and medical conditions that may develop as a result.
Down syndrome is a chromosomal disorder caused by an additional (third) chromosome 21 or "trisomy 21." It is associated with mental retardation, a characteristic facial appearance, and poor muscle tone (hypotonia).
This syndrome occurs in one out of 800 live births, in all races and economic groups. It is the most frequent genetic cause of mild to moderate mental retardation and associated medical problems.
The condition is caused by a genetic problem related to chromosome 21. While it is genetic in that it involves an extra chromosome 21, it is not usually hereditary in the conventional sense. That is, it is not inherited; it does not "run in families." The condition is usually the result of a random event that occurs during the formation of reproductive cells (eggs and sperm). One exception is Down syndrome caused by a balanced translocation (see Translocation and Down Syndrome).
As far as we know, it is not caused by any behavioral activity of the parents or environmental factors.
There are several established risk factors for this condition, including:
- Having a Down syndrome baby previously
- Increasing maternal age
- Carriers of a balanced translocation.