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Key Features

  • Risk of an affected fetus being conceived increases exponentially with age of mother at conception and begins a marked rise after age 35

  • At maternal age 45, risk is 1 in 40

Clinical Findings

  • Usually diagnosed at birth

  • Typical facial features: flat occiput, epicanthal folds, large tongue

  • Hypotonia

  • Single palmar crease

  • Serious problems at birth or early in childhood, such as

    • Duodenal atresia

    • Congenital heart disease (especially atrioventricular canal defects)

    • Hematologic malignancy

  • Intelligence varies across a wide spectrum

  • Alzheimer-like dementia in the fourth or fifth decade

  • Affected patients who survive childhood have a reduced life expectancy

  • Other frequent complications

    • Atlanto-axial instability

    • Celiac disease

    • Frequent infections due to immune deficiency

    • Hypothyroidism


  • Cytogenomic analysis

  • Most affected individuals have simple trisomy for chromosome 21

  • Others have unbalanced translocations, usually resulting from a parent with a balanced translocation, incurring a substantial risk of Down syndrome in future offspring

  • Can be detected in the early second trimester by

    • Screening maternal serum for α-fetoprotein and other biomarkers ("multiple marker screening")

    • Observation of increased nuchal skin thickness and underdevelopment of nasal bone on fetal ultrasonogram

  • Prenatal diagnosis with high sensitivity and specificity can be achieved by assaying fetal DNA circulating in maternal blood


  • No treatment has proved to affect neurodevelopmental or the neurodegenerative aspects

  • Duodenal atresia should be treated surgically

  • Congenital heart disease should be treated as in any other patient

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