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MTHFR is the rate-limiting enzyme in the methyl cycle, which includes the conversion of homocysteine into methionine. Defects in variants of MTHFR can therefore lead to hyperhomocysteinemia. [9] There are two common variants of MTHFR deficiency. In the more significant of the two, the individual is homozygous for the 677T polymorphism.
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 ...
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.
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]
Mutations in this gene can lead to reduced methylation at CpG sites, and these changes in methylation patterns may increase susceptibility for type 2 diabetes. The most common at the gene encoding MTHFR is the C677t mutation. This is not a spontaneous mutation; it is actually hereditary.
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 ]
A meta-analysis demonstrated that polymorphism of the MTHFR C677T genotype is correlated with an ASD diagnosis in children from countries lacking food fortification. [39] While MTHFR is a proposed genetic factor for ASD, there is limited clinical evidence from testing for MTHFR gene polymorphisms in the diagnostic setting. [40]
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.