How often does Down Syndrome occur/recur?
Down syndrome is the most common clinical cause of mental retardation in the world. It occurs once in every 1,500-2,000 births when the mother’s age is below 25; one in every 400 births when the mother’s age is over 35; once in every 40 births when the mother’s age is over 45. A mother with a child with Down syndrome has a one-in-25 chance of recurrence. Siblings of Down syndrome have the same risk of having a child with Down syndrome as does the general population unless the disorder is of genetic origin.
