Lejeune, Jérôme Jean Louis Marie (1926-1994)

French medical geneticist. Although the congenital condition known now as Down's syndrome was named after English physician J L H Down who studied it, it was Lejeune who discovered that Down's syndrome is the result of having an additional chromosome.

He believed chromosome deviations would in the future be treated by gene therapy, and vigorously opposed prenatal screening with a view to terminating Down's syndrome fetuses.

By the age of 26, Lejeune had completed his medical studies and was working with Raymond Turpin at the National Centre for Scientific Research in Paris. It was with Turpin and another colleague, Marthe Gautier, that in 1959 he published his discovery that Down's syndrome sufferers have one additional chromosome to the 46 previously determined to be the norm in humans. This was the first time that anyone had described a condition resulting from having the incorrect number of chromosomes. He went on to find that the cri du chat (‘cat cry’) syndrome is also caused by a numerical abnormality in human chromosomes where a small section of one of the longest chromosomes is missing.

In 1964 Lejeune was appointed professor of fundamental genetics in the Faculty of Medicine in Paris. He firmly believed in the ‘brotherhood’ of humanity; that the chromosome pattern of modern humans must have originated in a very small group of people - even one pair.