A genetic disorder (caused by the presence of an extra chromosome), which results in physical and mental abnormalities. Physical characteristics include a flattened face, widely spaced and slanted eyes, smaller head size and lax joints. Mental retardation is also typical, though there are wide variations in mental ability, behavior, and developmental progress. Possible related health problems include poor resistance to infection, hearing loss, gastrointestinal problems, and heart defects.
Source: Children Welfare Information Gateway