If we look at the basic phenotype of people with Down syndrome, it hasn’t changed much over the past 50 years. Most people with Down syndrome have common physical characteristics. They are also usually shorter than average. They commonly have low muscle tone, increased chances for various health conditions (such as heart defects and gastrointestinal issues), and mild to moderate intellectual disabilities. About 250,000 people in the US have Down syndrome, and about 1 in 800 babies are born with the condition.