Down Syndrome

Down syndrome is a set of cognitive and physical symptoms that result from having an extra chromosome 21 or an extra piece of that chromosome. It is the most common chromosomal cause of mild to moderate intellectual disabilities. People with Down syndrome also have some distinct physical features, such as a flat-looking face, and they are at risk for a number of other health conditions.

Understanding Down syndrome and other intellectual and developmental disabilities is part of the reason the NICHD was established. Today, the Institute continues to lead research on the causes, progression, treatment, and management of Down syndrome, as well as on conditions and diseases that are associated with the syndrome.

Common Name

  • Down syndrome

Medical or Scientific Names

  • Down syndrome
  • Trisomy 21
  • 47,XX,+21
  • 47,XY,+21
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