SayPro Homocysteine – An amino acid (one of the building blocks that makes up a protein) normally found in small amounts in the blood. Too much homocysteine in the blood may promote the buildup of fatty plaque in the arteries. For some people, high homocysteine levels are genetic. For others, it is because they do not get enough of certain B vitamins in their diet. (Common misspelling: homocystine)