Gene Symbol: MTHFR
Full Name: Methylenetetrahydrofolate Reductase
Chromosomal Location: 1p36.22
NCBI Gene ID: 4524
OMIM: 607093
Ensembl: ENSG00000177000
UniProt: P42830
Methylenetetrahydrofolate reductase (MTHFR) is a pivotal enzyme in one-carbon metabolism, catalyzing the reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate (5-MTHF), the primary circulating form of folate [1]. This reaction sits at the intersection of folate and homocysteine metabolism, making MTHFR a critical regulator of methyl group availability for DNA synthesis, epigenetic maintenance, and cardiovascular health [2].
The MTHFR gene encodes a 677-amino acid protein that functions as a homodimer, with each subunit containing a flavin adenine dinucleotide (FAD) cofactor essential for catalytic activity [3]. The enzyme is predominantly cytosolic and exhibits tissue-specific expression patterns, with highest activity in liver, kidney, and brain [4].
MTHFR catalyzes the irreversible reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate using NADPH as an electron donor:
5,10-methylene-THF + NADPH + H+ → 5-methyl-THF + NADP+
This reaction is rate-limiting in the folate cycle and serves two essential purposes:
MTHFR protein structure comprises:
The C677T polymorphism (rs1801133) substitutes valine for alanine at position 177, reducing FAD binding affinity by approximately 30-40%, resulting in a thermolabile enzyme variant with reduced catalytic efficiency [8].
MTHFR occupies a central node in one-carbon metabolism, connecting:
| Pathway | MTHFR Role |
|---|---|
| Folate cycle | Converts 5,10-methylene-THF to 5-MTHF |
| Homocysteine remethylation | Provides 5-MTHF as methyl donor |
| Methionine cycle | Enables methionine regeneration |
| DNA synthesis | Indirectly supports purine/pyrimidine synthesis |
| Epigenetic regulation | Provides methyl groups for SAM-dependent methylation |
The most extensively studied MTHFR variant, causing an alanine-to-valine substitution at codon 222:
Allele frequencies vary by population:
A second common polymorphism in the regulatory domain:
Compound heterozygotes for C677T and A1298C show intermediate activity (~35-40% of normal) [12].
The C677T polymorphism correlates with:
MTHFR polymorphisms, particularly C677T, have been extensively studied in Alzheimer's disease (AD):
Risk Association:
Mechanistic Pathways:
Homocysteine Neurotoxicity:
Amyloid Metabolism:
Vascular Contributions:
Clinical Evidence:
MTHFR variants have been linked to Parkinson's disease (PD) susceptibility and progression:
Risk and Progression:
Mechanistic Considerations:
Dopaminergic Neuron Vulnerability:
Levodopa Metabolism:
Evidence Summary:
Potential Associations:
Due to its role in vascular health, MTHFR variants contribute to:
Clinical Approaches:
Folate Supplementation:
Betaine (Glycine Betaine):
B-Vitamin Combinations:
Genotype-Guided Intervention:
Precision Nutrition:
MTHFR is expressed throughout the brain:
Folate transport across the blood-brain barrier involves:
MTHFR activity in brain is essential for:
Folate and MTHFR activity protect neurons through:
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