1. (n.)Down syndrome a genetic disorder associated with the presence of an extra chromosome 21, characterized by mental retardation, weak muscle tone, and epicanthic folds at the eyelids.
Etymology: (1960–65; after John L. H. Down (1828–96), British physician)
Definition of 'down syndrome'
Princeton's WordNet
1. (noun)mongolism, mongolianism, Down's syndrome, Down syndrome, trisomy 21 a congenital disorder caused by having an extra 21st chromosome; results in a flat face and short stature and mental retardation
Definition of 'down syndrome'
U.S. National Library of Medicine
1. down syndrome A chromosome disorder associated either with an extrachromosome 21 or an effective trisomy for chromosome 21. Clinical manifestations include hypotonia, short stature, brachycephaly, upslanting palpebral fissures, epicanthus, Brushfield spots on the iris, protruding tongue, small ears, short, broad hands, fifth finger clinodactyly, Simian crease, and moderate to severe MENTAL RETARDATION. Cardiac and gastrointestinal malformations, a marked increase in the incidence of LEUKEMIA, and the early onset of ALZHEIMER DISEASE are also associated with this condition. Pathologic features include the development of NEUROFIBRILLARY TANGLES in neurons and the deposition of AMYLOID BETA-PROTEIN, similar to the pathology of ALZHEIMER DISEASE. (Menkes, Textbook of Child Neurology, 5th ed, p213)
Definitions of down syndrome 
