Down syndrome, also called Down’s syndrome (DS), is the most common chromosomal condition associated with intellectual disability and is characterized by a variety of additional clinical findings. It occurs in approximately 1 of 800 births worldwide. In the United States, DS accounts for approximately 500 live births annually, and more than 200,000 persons are living with the disorder. The original description of the syndrome, in 1866, has been attributed to John Langdon Down, a physician from Cornwall, England. More than 90 years later, the chromosomal cause was delineated and the condition was named Down syndrome.
Source: Marilyn J. Bull, MD