Syndrome - Definition
Down syndrome is the most common and readily identifiable
chromosomal condition associated with mental retardation. It 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.
Approximately 4,000 children with Down syndrome are born in the U.S. each
year, or about 1 in every 800 to 1,000 live births. Although parents of
any age may have child with Down syndrome, the incidence is higher for
women over 35. Most common forms of the syndrome do not usually occur
more than once in a family.