Judged: two independent readers; copy check clear.
Down syndrome
Down syndrome Down syndrome is a chromosome disorder caused by an extra chromosome 21 or its equivalent.
Down syndrome is a chromosome disorder caused by an extra chromosome 21 or its equivalent. It is associated with a characteristic pattern of physical features, moderate to severe intellectual disability, and increased risk of certain medical problems including heart and gastrointestinal abnormalities, leukemia, and early-onset Alzheimer disease.