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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-Ãtienne Dominique Esquirol in 1838 and Ãdouard SÃ©guin in 1844. In 1957, the genetic cause of Down syndrome, an extra copy of chromosome 21, was discovered.
Jerome Lejeune, a French geneticist who discovered the chromosome abnormality in humans that causes Down syndrome, a common form of mental retardation, died on April 3 in Paris. He was 67 and lived in Paris.erome Lejeune, a French geneticist who discovered the chromosome abnormality in humans that causes Down syndrome, a common form of mental retardation, died on April 3 in Paris. He was 67 and lived in Paris.