Homocysteine is a non-proteinogenic amino acid, a homologue of the amino acid cysteine (homologues are the substances that have the same structure but differ from one another in composition by one or more groups -CH2-). In the body homocysteine is produced from methionine and can be converted back into methionine when vitamin B is present. High levels of homocysteine (hyperhomocysteinemia) has negative impact on endothelium (the layer of cells lining the interior surface of the blood vessels and lymphatic vessels). Particularly, it damages the endothelium and results in inflammation of the tissue leading to thrombogenesis, atherosclerosis and related to these conditions ischemic damage. Increased levels of homocysteine affect negatively not just the structure of the vascular wall but also the blood coagulation system.