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Methylenetetrahydrofolate reductase (MTHFR) is the rate-limiting enzyme in the methyl cycle, and it is encoded by the MTHFR gene. [5] Methylenetetrahydrofolate reductase catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate , a cosubstrate for homocysteine remethylation to methionine .
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]
Methylenetetrahydrofolate dehydrogenase, cyclohydrolase and formyltetrahydrofolate synthetase 1 (MTHFD1) is a gene located in humans on chromosome 14 [4] that encodes a protein, C-1-tetrahydrofolate synthase, cytoplasmic also known as C1-THF synthase, with three distinct enzymatic activities.
A deficiency of folate itself does not cause neural tube defects. The association seen between reduced neural tube defects and folic acid supplementation is due to a gene-environment interaction such as vulnerability caused by the C677T methylenetetrahydrofolate reductase (MTHFR) variant.
Cerebral folate deficiency is a condition in which concentrations of 5-methyltetrahydrofolate are low in the brain as measured in the cerebral spinal fluid despite being normal in the blood. [3]
Methylenetetrahydrofolate dehydrogenase 1 deficiency (MTHFD1 deficiency) is a disease resulting from mutations of the MTHFD1 gene. Patients with this disease may have hemolytic uremic syndrome, macrocytosis, epilepsy, hearing loss, retinopathy, mild mental retardation, lymphocytopenia (involving all subsets) and low T-cell receptor excision circles.
Thymidylate synthase is an enzyme of about 30 to 35 kDa in most species except in protozoan and plants where it exists as a bifunctional enzyme that includes a dihydrofolate reductase domain. [8] A cysteine residue is involved in the catalytic mechanism (it covalently binds the 5,6-dihydro-dUMP intermediate).
Co-expression of this mutation and the 677T polymorphism in methionine tetrahydrofolate reductase (MTHFR) Methylenetetrahydrofolate reductase act to further the extent of DNA damage. [36] Hypomethylation due to impaired methylation up regulates atherosclerotic susceptible genes whilst down regulating atherosclerosis protective genes. [36]