- Last edited on April 30, 2020
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Down Syndrome (Trisomy 21)
Primer
Down Syndrome (Trisomy 21) is the most common identifiable genetic cause of intellectual disability. It is due to the presence of all or part of a third copy of chromosome 21. Individuals with Down syndrome have a characteristic facial appearance and hypotonia in infancy. About half are born with a heart defect.
Epidemiology
The prevalence varies in different populations, anywhere from 1 in 319 to 1 in 1000 births.[1] The incidence of Down syndrome increases significantly with maternal age.
Comorbidity
Down syndrome is also associated with an increased risk of developing early onset Alzheimer's disease.
Diagnosis
Pathophysiology
In the majority of cases, Down syndrome is not hereditary.