Down syndrome is the term for a set of cognitive and physical symptoms that can result from having an extra copy or part of a copy of chromosome 21.
Down syndrome is the most frequent chromosomal cause of mild to moderate intellectual disability, and it occurs in all ethnic and economic groups.
The degree of intellectual disability in people with Down syndrome varies but is usually mild to moderate. Generally, children with Down syndrome reach key developmental milestones later than other children.
According to the Centers for Disease Control and Prevention, approximately 6,000 babies are born in the United States each year with Down syndrome, or approximately 1 out of every 691 live births.
In recent decades, thanks to appropriate support and treatment, life expectancy for people with Down syndrome has increased dramatically: from 25 years in 1983 to more than 60 years today.