Is it inherited?
Most of the time, Down syndrome isn't inherited. It's caused by a mistake in cell division during the development of the egg, sperm or embryo.
Translocation Down syndrome is the only form of the disorder that can be passed from parent to child. However, only about 4 percent of children with Down syndrome have translocation. And only about half of these children inherited it from one of their parents.
When translocations are inherited, the mother or father is a balanced carrier of the translocation, which means he or she has some rearranged genetic material, but no extra genetic material. A balanced carrier has no signs or symptoms of Down syndrome, but he or she can pass the translocation on to children.
The chance of passing on the translocation depends on the sex of the parent who carries the rearranged chromosome 21:
- If the father is the carrier, the risk is about 3 percent.
- If the mother is the carrier, the risk is between 10 and 15 percent.
