NCIt definition : A chromosomal abnormality consisting of the presence of a third copy of chromosome
21 in somatic cells.;
Alternative definition : ACC/AHA: A chromosomal abnormality consisting of the presence of part or all of a
third copy of chromosome 21 in somatic cells.;
https://www.pedia-univ.fr/deuxieme-cycle/referentiel/enfant-vulnerable-genetique/trisomie-21 2024 France educational course trisomy Trisomy 21 down syndrome Down Syndrome