It was later determined that an extra partial or whole copy of chromosome 21 results in the characteristics associated with Down syndrome. Instead of the usual 46 chromosomes present in each cell, Lejeune observed 47 in the cells of individuals with Down syndrome.
In 1959, the French physician Jérôme Lejeune identified Down syndrome as a chromosomal condition. In recent history, advances in medicine and science have enabled researchers to investigate the characteristics of people with Down syndrome. Although other people had previously recognized the characteristics of the syndrome, it was Down who described the condition as a distinct and separate entity. It was this scholarly work, published in 1866, that earned Down the recognition as the “father” of the syndrome. It wasn’t until the late nineteenth century, however, that John Langdon Down, an English physician, published an accurate description of a person with Down syndrome. For centuries, people with Down syndrome have been alluded to in art, literature, and science.
