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Methylenetetrahydrofolate reductase deficiency is the most common genetic cause of elevated serum levels of homocysteine (hyperhomocysteinemia). It is caused by genetic defects in MTHFR, which is an important enzyme in the methyl cycle. [1] Common variants of MTHFR deficiency are asymptomatic and have only minor effects on disease risk. [2]
In studies of human recombinant MTHFR, the protein encoded by 1298C cannot be distinguished from 1298A in terms of activity, thermolability, FAD release, or the protective effect of 5-methyl-THF. [22] The C mutation does not appear to affect the MTHFR protein. It does not result in thermolabile MTHFR and does not appear to affect homocysteine ...
The most common polymorphisms are known as MTHFR C677T and MTR A2756G. [23] [24] The homozigote mutation G;G also called C;C (it is equivalent) occurs in about 10% of the population of european ethnicity (white caucasians). [25] Elevations of homocysteine can also occur in the rare hereditary disease homocystinuria. [citation needed]
There is an association between the blood levels of homocysteine and thrombosis, [16] although this has not been reported consistently in all studies. [5] Homocysteine levels are determined by mutations in the MTHFR and CBS genes, but also by levels of folic acid, vitamin B 6 and vitamin B 12, which depend on diet. [14]
Total plasma homocysteine. Homocysteine levels typically are higher in men than women, and increase with age. [15] [16] Common levels in Western populations are 10 to 12 μmol/L, and levels of 20 μmol/L are found in populations with low B-vitamin intakes or in the elderly (e.g., Rotterdam, Framingham). [17] [18]
Elevated homocysteine is an independent risk factor for cardiovascular disease and inversely correlated to consumed vitamin B12/B6 and folate levels. [37] Homocysteine methylation to methionine is catalyzed by MTR, resulting in appropriate intracellular levels of methionine and tetrahydrofolate, alongside non-toxic homocysteine levels.
Levomefolic acid (INN, also known as L-5-MTHF, L-methylfolate and L-5-methyltetrahydrofolate and (6S)-5-methyltetrahydrofolate, and (6S)-5-MTHF) is the primary biologically active form of folate used at the cellular level for DNA reproduction, the cysteine cycle and the regulation of homocysteine.
C677T or rs1801133 is a genetic variation—a single nucleotide polymorphism (SNP)—in the MTHFR gene. Among Americans the frequency of T-homozygosity ranges from 1% or less among people of sub-Saharan African descent to 20% or more among Italians and Hispanics. [1] It has been related to schizophrenia [2] Alzheimer's disease [3] depression [4 ...