What causes Down syndrome?
Researchers are still trying to understand why Down syndrome occurs, but the condition is the result of extra genetic material on the 21st chromosome. While most people have only two copies of the 21st chromosome, something occurs during cell development to give persons with Down syndrome three copies.
Down syndrome is a chromosomal disorder caused by an error in cell division that results in an extra 21st chromosome. The condition leads to impairments in both cognitive ability and physical growth that range from mild to moderate developmental disabilities. Through a series of screenings and tests, Down syndrome can be detected before and after a baby is born. The only factor known to affect the probability of having a baby with Down syndrome is maternal age. That is, less than one in 1,000 pregnancies for mothers less than 30 years of age results in a baby with Down syndrome. For mothers who are 44 years of age, about 1 in 35 pregnancies results in a baby with Down syndrome. Because younger women generally have more children, about 75 – 80% of children with Down syndrome are born to younger women.
