Down syndrome is the most common chromosomal condition associated with mental retardation. It is caused by a child's having an extra chromosome, a result of an accident in cell development. This extra chromosome changes the orderly development of the body and brain. Down syndrome is usually confirmed by a chromosome test administered shortly after birth.
Approximately 4000 children with Down syndrome are born in the U.S. each year, or 1 in every 800 to 1000 live births. Children with Down syndrome are usually smaller than their peers, with delayed physical, intellectual, motor and language development.
A distinct physical appearance includes poor muscle tone; slanting eyes with folds of skin at the inner corners; short hands, feet, neck and ears; and hyperflexibility. Children with Down syndrome also frequently have specific health-related problems, which may include a lowered resistance to infection, respiratory problems, visual problems, hearing loss, heart defects, and a tendency to obesity as they grow older.
Most children with Down syndrome function in the mild to moderate range of mental retardation. However, some are not mentally retarded, but in the borderline to low average range, while others are severely mentally retarded. Research shows that intervention and stimulation in the early years improves the child's chances of developing to fullest potential. Continuing education, positive public attitudes, and a caring, enriching home environment are also important.