Trisomy 21 is a genetic disease that affects the whole person. It results from a chromosomal anomaly: normally, the man has 46 chromosomes (cf lexicon) organized in 23 pairs. In trisomy 21, chromosome 21 is in three copies instead of two, bringing the total number of chromosomes to 47. Chromosome 21 is the smallest of the chromosomes, with approximately 255 genes.

It is the presence of this extra chromosome that throws the whole genome and therefore the organism off balance.

This genetic disease can be compared to a computer with too many applications open at the same time. The computer is not broken; it is still running…but in slow motion, because it cannot manage all this information at the same time. In order to get it working again at a good speed, you have to close some windows.

Scientific research aims to silence the excess information expressed in these patients (the “over-expression of chromosome 21”), by inhibiting some of the over-expressed genes from the extra chromosome 21.