The clinical consequences of having three copies of chromosome 21. The condition is marked by mild to moderate mental retardation and physical characteristics that include a sloping forehead, low-set ears with small canals, and short broad hands with a single palmar crease (“simian” crease). Cardiac valvular disease and a tendency to develop Alzheimer-like changes in the brain are common consequences of the syndrome. The syndrome is present in about 1 in 700 births in the U.S. and is more common in women over age 34 or when the father is older than 42. In women who conceive after age 45, the incidence rises dramatically.
A genetic disorder resulting from an extra chromosome; people with Down syndrome are mentally retarded, may have heart defects, and have a distinctive physical appearance.
In the realm of genetic disorders, there exists a condition known as Down syndrome, which arises from the presence of an additional copy or a rearrangement of chromosome 21. Children affected by Down syndrome display a range of intellectual disability (ID) with varying degrees of severity. Additionally, it is not uncommon for individuals with Down syndrome to have associated heart defects, further contributing to the complexity of the condition.