The father of modern genetics, Dr. Jérôme Lejeune discovered in 1959 the extra chromosome 21 responsible for the condition known as Down syndrome, which he called trisomy 21. Inspired by a deep belief that a cure for trisomy 21 would be found one day and that medicine has a duty to serve society's weakest members, Lejeune dedicated his life to research and to caring for the intellectually disabled. Written by his daughter.