Homocysteine is a small molecule. It is chemically an amino acid. Several amino acids join together to form polymeric molecules called proteins. Unlike many other amino acids, homocysteine is only an intermediate in the metabolism of the amino acid methionine and cannot be found in proteins. Hence, homocysteine is a non protein amino acid.
Coronary heart disease is a serious disease which may, ultimately lead to the occurrence of fatal heart attacks. Unlike diabetes which is characterized by the presence of several useful diagnostic tests, coronary heart disease cannot be detected with 100% accuracy. However, several tests have been developed to predict the risk for coronary heart disease. For example, increases in the circulating levels of cholesterol and LDL cholesterol have always been associated with cardiovascular disease. Increase in the levels of pro inflammatory C-reactive protein has also been associated with cardiovascular disease.
The discovery of a congenital disorder called homocystinuria has led to the development of yet another diagnostic tool for predicting the risk for heart attacks. This inborn error of metabolism is characterized by increased circulating levels of the amino acid homocysteine. The children suffering from this rare disorder died at a very young age from heart attacks and their coronary arteries showed severe atherosclerotic lesions. Thus, high circulating levels of homocysteine have been recognized as indicating increased risk for heart attacks. Homocysteine accumulates in homocystinuria because of the congenital deficiency of an enzyme called cystathionine beta synthase.
Deficiency of B-vitamins B12, B6 and folic acid ha s also been seen to cause an elevation in the circulating levels of homocysteine. However, it is not clear as to whether vitamin supplementation could completely reverse the atherosclerotic process. Several mechanisms have been proposed to account for the heart attack promoting nature of homocysteine. One theory suggests that homocysteine itself is toxic at high concentrations and may damage the inner lining of the arteries. LDL has been called the bad cholesterol. However, it is the oxidized form of LDL which is more dangerous. It has been suggested that homocysteine may promote the oxidation of LDL. It has also been shown that homocysteine has the ability to interfere with the clotting process.