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Trisomy 21

"21 Thoughts" by Dr. Jerome Lejeune

The father of modern genetics, Dr. Jerome Lejeune, discovered that an extra copy of chromosome 21 was responsible for the condition known as Down syndrome.

Trisomy 21 (Down syndrome)

What is Trisomy 21, or Down Syndrome?

Our Work

In 1958, Professor Jerome Lejeune, a doctor and researcher at the Necker Hospital in Paris, discovered an extra chromosome on the 21st pair and in so doing discovered the genetic cause of Down syndrome.

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Improving Joyful Lives. A new paper on Down syndrome prepared by the Jerome Lejeune Foundation

Down syndrome is a highly complex genetic condition, but it is also a highly complex sociological...


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Jerome Lejeune Foundation