Kolkata: Down Syndrome is a type of mental retardation caused by extra genetic material in chromosome 21.
This can be due to a process called nondisjunction, in which genetic materials fail to separate during a crucial part of the formation of gametes, resulting in an extra chromosome (called trisomy 21).
The cause of nondisjunction is not known, although it correlates with a woman's age reference. The additional material present influences development and results in the state known as Down Syndrome.
Some physical characteristics of Down Syndrome in infants are decreased muscle tone, a flat face, eyes slanting up, irregular shaped ears, ability to extend joints beyond the usual, large space between the big toe and its neighbouring toe and large tongue relative to the mouth.
According to World Health Organization (WHO), Down Syndrome patients can also be afflicted with other conditions, including heart disease, Alzheimer's disease, and leukaemia.
The estimated incidence of Down Syndrome is between 1 in 1,000 to 1 in 1,100 live births worldwide. Each year approximately 3,000 to 5,000 children are born with this chromosome disorder and it is believed there are about 250,000 families in the United States of America who are affected by Down Syndrome.
Sixty to 80 per cent of children with Down Syndrome have hearing deficits. Forty to 45 per cent of children with Down Syndrome have congenital heart disease. Intestinal abnormalities also occur at a higher frequency in children with Down Syndrome.