Down syndrome is the most common and readily identifiable chromosomal condition associated with mental retardation. Down syndrome is caused by a chromosomal abnormality: for some unexplained reason, an accident in cell development results in 47 instead of the usual 46 chromosomes. This extra chromosome changes the orderly development of the body and brain. In most cases, the diagnosis of Down Syndrome is made according to results from a chromosome test administered shortly after birth.
From: Down Syndrome Fact Sheet – NICHCY
More people in the U.S. have Cerebral Palsy than any other developmental disability, including Down syndrome.
The percentage of children with both Down syndrome and Cerebral Palsy is significantly lower than expected, according to several studies. Most of the children in these studies appear to have developed Cerebral Palsy after birth. Since Cerebral Palsy often occurs due to brain damage from lack of oxygen before or during birth, researchers are exploring the possibility that fetuses and infants with Down syndrome may be resistant to the development of pre-natal cerebral palsy. Their findings may help lead to a way of lowering the risk of Cerebral Palsy in children without Down syndrome.