1926-1994

French geneticist who discovered the chromosomal abnormality linked to Down's syndrome. During the 1950s, while at the National Center for Scientific Research (CNRS) in Paris, Lejeune conducted research concerning genetic predisposition for Down's syndrome, a congenital form of mental retardation. In 1959 he discovered that normal children were born with 46 chromosomes, or 23 pairs of chromosomes, while children with Down's syndrome exhibited an extra chromosome, which made one of the pairs a triplet. Lejeune was appointed director of research at the CNRS in 1963, and professor of fundamental genetics at the Faculty of Medicine in Paris in 1964.