Down syndrome started in 2015.
Down syndrome . In 2015 , Down syndrome was present in 5.4 million individuals and resulted in 27,000 deaths down from 43,000 deaths in 1990 . It is named after John Langdon Down , the British doctor who fully described the syndrome in 1866 . Some aspects of the condition were described earlier by Jean-Étienne Dominique Esquirol in 1838 and Édouard Séguin in 1844 . In 1957 , the genetic cause of Down syndrome , an extra copy of chromosome 21 , was discovered .