Physician and genetics researcher, Jérôme Lejeune acquired an international reputation in 1958 when he discovered the Trisomy 21, cause of Down Syndrome. He hoped his discovery would change the way people looked at children with Down Syndrome, who came by hundreds to his medical consultations. He had only one obsession : to find someday a cure. The meteoric rise of this young French scientist will be be stopped in a flash in 1969. While receiving the William Allen Award in San Francisco, the highest award in genetics, he delivered a speech defending the human dignity of the embryo, causing an earthquake in the scientific sphere. A few months before, he realized that his discovery would be used against his convictions, by opening the door to abortion of embryos with genetic abnormalities. Who was Jérôme Lejeune? A great scientist or a man of faith ? Nowadays what is the state of research on Trisomy 21, in which he had placed so much hope? 20 years after his death, the director François Lespes wondered about this man's complex personality, who had such an extraordinary fate. « Jerome Lejeune - To the least of these my brothers & sisters » is investigating on the man of science and beliefs, from Paris to Indianapolis, from friends to confrères, from supporters to detractors.