Down syndrome

n. A congenital condition characterized by mild to severe mental retardation, pleasant disposition, a flat face, stubby fingers and toes, epicanthic folds in the eyes among non- Asians, tongue fissures, and unusual patterns of skinfolds on the palms of the hands and soles of the feet. It is caused by the presence of an extra chromosome 21 or, in rare cases, by an extra copy of chromosome 22 and is associated with an early onset of Alzheimer’s disease.