English physician John Langdon Down first described Down syndrome in 1862, recognizing it as a distinct type of mental disability. By the 20th century, Down syndrome had become the most recognizable form of mental disability.
With the discovery of karyotype techniques in the 1950s, it became possible to identify abnormalities of chromosomal number or shape.
In 1959, Jérôme Lejeune reported the discovery that Down syndrome resulted from an extra chromosome. As a result of this discovery, the condition became known as trisomy 21.
Keyword: history down syndrome