Down Syndrome Down syndrome is one of the most common birth defects. Usually, children born with the condition have some degree of mental retardation, as well as characteristic physical features. Many of these children also have other health problems. Each year in the United States, approximately one in every 800 to 1,000 newborns has Down syndrome. This translates to approximately 5,000 children. In the United States today, Down syndrome affects approximately 350,000 people. The life expectancy for a child born today with Down syndrome is approximately 55 years. The most common form of Down syndrome is ofte