[Hyperhomocysteinemia in neurologic diseases].

Homocysteine is a thyol amino acid resulting from a methylation of methionine, an essential amino acid derived from dietary proteins. Homocysteine is metabolized through two pathways: remethylation and transsulfuration, which use as confactors folic acid, vitamin B6 and vitamin B12. The genetic and acquired factors that induce a reduction of levels of folic acid, vitamin B6 and vitamin B12 cause an increase of plasma levels of homocysteine. Numerous clinical studies showed a relationship between hyperhomocysteinemia, cerebrovascular diseases and Alzheimer disease. The hyperhomocysteinemia is also demonstrated in patients with Parkinson disease treated with levodopa and in the epileptic patients treated with anticonvulsant drugs. Nevertheless, so far it is not fully clear how significant is the relationship between the hyperhomocysteinemia and the above-mentioned neurological diseases.