Down Syndrome - Genetics

Genetics

Down syndrome disorders are based on having too many copies of the genes located on chromosome 21. In general, this leads to an overexpression of the genes. Understanding the genes involved may help to target medical treatment to individuals with Down syndrome. It is estimated that chromosome 21 contains 200 to 250 genes. Recent research has identified a region of the chromosome that contains the main genes responsible for the pathogenesis of Down syndrome.

The extra chromosomal material can come about in several distinct ways. A typical human karyotype is designated as 46,XX or 46,XY, indicating 46 chromosomes with an XX arrangement typical of females and 46 chromosomes with an XY arrangement typical of males. In 1–2% of the observed Down syndromes. some of the cells in the body are normal and other cells have trisomy 21, this is called mosaic Down syndrome (46,XX/47,XX,+21).