Homocysteine is an amino acid with the formula HSCH2CH2CH(NH2)CO2H. It is a homologue of the amino acid cysteine, differing by an additional methylene (CH2) group. It is biosynthesized from methionine by the removal of its terminal C epsilon methyl group. Homocysteine can be recycled into methionine or converted into cysteine with the aid of B vitamins. While detection of high levels of homocysteine has been linked to cardiovascular disease, lowering homocysteine levels may not improve outcomes. Synonyms: Homocystein control.