Down syndrome

  • Definition

    Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46.


    Alternative Names

    Trisomy 21


    Causes, incidence, and risk factors

    In most cases, Down syndrome occurs when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21. The extra chromosome causes problems with the way the body and brain develop.

    Down syndrome is the most common single cause of human birth defects.