0 a condition in which someone is born with an extra chromosome (= one of the rod-like structures found in all living cells which is part of an animal's or plants genetic material), which results in them having learning difficulties:
The screening test might say your child has a one in 350 chance of having Down syndrome.
We think we're slowly being able to understand what's causing reduced cognitive ability in people with Down syndrome.
She is a mother of four children, including a Down syndrome baby.
