Down syndrome or Down’s syndrome (DS) is a genetic condition that occurs as a result of an extra chromosome (chromosome 21).
The extra chromosome appears due to an error in cell division at conception called nondisjunction. The causes are unknown. (Source: National Association for Down Syndrome)
According to the American National Down Syndrome Society, there are three types:
Trisomy 21 (nondisjunction – in which every cell in the body has an extra copy of chromosome 21) accounts for 95 per cent of cases.
Translocation (when a piece of chromosome 21 attaches itself to another chromosome in a cell) accounts for about 4 pent of cases.
Mosaicism (in which only some of the cells have an extra copy of chromosome 21) accounts for about 1 per cent of cases.
The older the mother, the higher the chances of the baby having DS. However, babies with DS are born to mothers of all ages and over half are born to mothers who are under 35. The incidence of DS among Emiratis in Dubai is one in every 320 births (1:319), higher than the world average of 1 in every 800 births (data released by the Centre for Arab Genomic Studies (CAGS))