Hyperhomocysteinemia

Hyperhomocysteinemia is a medical condition characterized by an abnormally high level of total homocysteine (that is, including homocystine and homocysteine-cysteine disulfide) in the blood, conventionally described as above 15 μmol/L. As a consequence of the biochemical reactions in which homocysteine is involved, deficiencies of vitamin B6, folic acid (vitamin B9), and vitamin B12 can lead to high homocysteine levels. Other possible causes of hyperhomocysteinemia include genetics, excessive methionine intake, and other diseases. Hyperhomocysteinemia is typically managed with vitamin B6, vitamin B9 and vitamin B12 supplementation. Hyperhomocysteinemia is a risk factor for cardiovascular disease; however, supplements of these vitamins may not improve cardiovascular disease outcomes. Elevated levels of homocysteine have been associated with a number of disease states. Elevated homocysteine is a known risk factor for cardiovascular disease as well as thrombosis. It has also been shown to be associated with microalbuminuria which is a strong indicator of the risk of future cardiovascular disease and renal dysfunction. Homocysteine degrades and inhibits the formation of the three main structural components of arteries: collagen, elastin and proteoglycans. In proteins, homocysteine permanently degrades cysteine disulfide bridges and lysine amino acid residues, affecting structure and function. Evidence exists linking elevated homocysteine levels with vascular dementia and Alzheimer's disease. There is also evidence that elevated homocysteine levels and low levels of vitamin B6 and B12 are risk factors for mild cognitive impairment and dementia. Oxidative stress induced by homocysteine may also play a role in schizophrenia. Elevated levels of homocysteine have also been linked to increased fractures in elderly persons. Homocysteine auto-oxidizes and reacts with reactive oxygen intermediates, damaging endothelial cells and increasing the risk of thrombus formation. Homocystinuria is the second most common cause of heritable ectopia lentis.