It is important to realize that technically, Down Syndrome and Trisomy 21 are different. It is theoretically possible for someone to have Trisomy 21, and not have Down Syndrome. A syndrome is a list of symptoms. A trisomy is a chromosomal abnormality. Because of Trisomy 21, gene products of chromosome 21 are overexpressed 50%. The effect of having too much of these products is Down Syndrome. For an example, take the SOD gene, which is on chromosome 21. When you breathe, your body takes some of that air and turns it into superoxide, a poisonous form of oxygen that destroys cells. SOD is an enzyme that takes the dangerous superoxide and turns it into hydrogen peroxide. Then another enzyme called glutathione peroxidase takes the hydrogen peroxide and turns it into harmless oxygen and water. However, in Down Syndrome, there is half-again as much SOD makes half-again as there's supposed to be. That would be fine, except the enzyme glutathione peroxidase is on another chromosome, and therefore there is not enough of it to change hydrogen peroxide into oxygen and water. Hydrogen peroxide is very destructive to cells, including brain cells. Having too much of it is not good. The solution to this is to supplement antioxidants, like vitamin C or vitamin E. They can sop up the excess hydrogen peroxide. This category has sites in it that give information on supplementing those with Trisomy 21. TNI stands for targeted nutritional intervention.
More information