MTHFD1 Gene Test (Methylenetetrahydrofolate Dehydrogenase 1)

MTHFD1 encodes a cytosolic trifunctional enzyme with three activities in a single protein: 5,10 methylenetetrahydrofolate dehydrogenase, 5,10 methenyltetrahydrofolate cyclohydrolase, and 10 formyltetrahydrofolate synthetase. Together, these activities interconvert one carbon substituted tetrahydrofolate derivatives that feed de novo purine synthesis, thymidylate synthesis, and remethylation of homocysteine to methionine.

The enzyme contains an amino terminal domain with dehydrogenase and cyclohydrolase activities and a larger synthetase domain that generates 10 formyltetrahydrofolate from formate and tetrahydrofolate. Rare, severe loss of function mutations in MTHFD1 can cause methylenetetrahydrofolate dehydrogenase 1 deficiency with combined immunodeficiency, megaloblastic anaemia, and hyperhomocysteinaemia, while common polymorphisms such as G1958A are associated with more modest shifts in enzyme behaviour and risk patterns.

MTHFD1 acts as a central hub in cytosolic one carbon metabolism, directing one carbon units carried on tetrahydrofolate into three key destinations: purine synthesis, thymidylate synthesis, and methionine generation via homocysteine remethylation. By interconverting 5,10 methylenetetrahydrofolate, 5,10 methenyltetrahydrofolate, and 10 formyltetrahydrofolate, it helps balance nucleotide production with methylation needs according to cellular demand.

When MTHFD1 activity is reduced or biased by genetics or limited folate availability, competition for limited one carbon donors can intensify, potentially favouring DNA synthesis at the expense of methylation, or vice versa, depending on context. This can subtly influence homocysteine levels, DNA repair fidelity, global DNA methylation patterns, and susceptibility to conditions linked to folate status such as neural tube defects and some cancers when other factors are not well supported.

MTHFD1 supports three interconnected domains: nucleotide synthesis, methylation capacity, and homocysteine regulation through its role in one carbon metabolism. These processes underpin cell division, embryonic development, vascular integrity, and long term genomic stability.

Research has associated the G1958A polymorphism with maternal risk for neural tube defects, cleft lip, congenital heart defects, and with patterns in cardiovascular and cancer risk, often through effects on homocysteine and DNA methylation. Some studies suggest that certain MTHFD1 genotypes may carry higher neural tube defect risk but also show a complex relationship with cancer risk and DNA methylation status, underlining that nutrient status, choline intake, and broader environment strongly influence how these variants express.

It is easy to conflate MTHFD1 and MTHFR because both belong to the folate pathway, but they sit at different control points. MTHFD1 interconverts multiple one carbon forms of tetrahydrofolate and links formate and choline derived one carbon units into purine and thymidylate synthesis and methionine generation. MTHFR, by contrast, specifically converts 5,10 methylenetetrahydrofolate into 5 methyltetrahydrofolate for homocysteine remethylation.

This distinction matters because MTHFD1 influences the overall pool and distribution of one carbon donors, while MTHFR governs a specific branch. A person can have a typical MTHFR genotype but carry MTHFD1 variants that increase choline demand or subtly change neural tube defect risk, or vice versa. Looking across the network, rather than a single gene, gives a more accurate view of one carbon metabolism.

The impact of MTHFD1 variants is shaped more by nutrient status, choline availability, pregnancy demands, and broader physiology than by the gene alone. Several modifiable factors can buffer or amplify MTHFD1 related tendencies.

• Folate intake and quality: Adequate folate intake from leafy greens, legumes, and, where appropriate, folate supplements supports one carbon pools and can soften the impact of reduced MTHFD1 activity. Low folate intake or malabsorption can make the same variant more clinically relevant.
• Choline intake and methyl donors: Choline can supply one carbon units and act as an alternative methyl donor when folate pathways are under pressure. People with certain MTHFD1 variants may have a higher choline requirement and can benefit from adequate choline intake through diet or, where appropriate, supplementation.
• Vitamin B12 and B6 status: B12 and B6 sit at key points in the homocysteine and methylation network. Deficiencies can raise homocysteine and strain methylation even when MTHFD1 function is intact, and can compound genetic tendencies when MTHFD1 activity is reduced.
• Pregnancy and preconception status: During preconception and pregnancy, demand for nucleotide synthesis and methylation rises sharply. MTHFD1 variants, especially when combined with low folate or choline intake, may contribute to neural tube defect risk in mothers, making periconceptional folate and choline optimisation particularly important.
• Metabolic and cardiovascular health: Kidney function, metabolic syndrome, and overall inflammatory status can influence homocysteine levels and how one carbon metabolism is utilised. Improving these domains often has a larger effect on cardiovascular risk than genotype alone.

Yes, and this is common. Many people carry MTHFD1 polymorphisms such as G1958A without developing clear folate related symptoms, and only learn about their genotype through DNA testing or comprehensive methylation panels.

Symptoms sometimes attributed to "methylation issues," such as fatigue, low mood, or brain fog, are non specific and can arise from sleep problems, iron or B12 deficiency, thyroid dysfunction, mental health conditions, or lifestyle factors. Severe MTHFD1 deficiency with combined immunodeficiency, megaloblastic anaemia, and marked hyperhomocysteinaemia is rare and distinct from the common polymorphisms seen in the general population.

Common MTHFD1 genotypes differ mainly in how they alter enzyme stability or the balance among its three activities, and how strongly they influence one carbon metabolism under nutritional or physiological stress. Understanding your pattern can help fine tune folate and choline support and monitoring.

• G1958A (R653Q) variants: The G1958A polymorphism, which changes an amino acid in the synthetase domain, has been widely studied. Certain genotypes have been associated with altered neural tube defect risk in mothers, shifts in homocysteine and DNA methylation, and nuanced differences in cancer risk patterns across studies. Effect sizes are typically modest and context dependent.
• Reference or "typical" genotypes: Individuals with reference MTHFD1 genotypes generally have full enzyme capacity, so one carbon metabolism depends more on folate and choline intake, B vitamin status, and metabolic health than on MTHFD1 itself.
• Rare pathogenic variants: Rare loss of function mutations in MTHFD1 can cause severe deficiency syndromes and are managed in specialist care. These are not the focus of standard preventive gene panels but highlight how essential this enzyme is for one carbon metabolism.

For DNA based MTHFD1 testing, preparation is straightforward because genotype does not change with meals, sleep, or exercise. The main consideration is ensuring the test panel includes key polymorphisms such as G1958A and aligns with your preventive or clinical questions.

Standalone MTHFD1 genotyping using blood or saliva does not require fasting, since it targets stable DNA sequence rather than dynamic folate or homocysteine levels. If MTHFD1 is bundled with tests like homocysteine, folate, B12, choline markers, lipids, or glucose, follow any fasting or timing guidance so that follow up results are easier to compare.

An MTHFD1 test is most useful when the results will influence folate and choline strategies, preconception planning, or cardiovascular and cancer prevention discussions as part of a broader approach. It is less helpful when done in isolation without homocysteine, folate, B12, and clinical context.

• Preconception and pregnancy planning: For people planning pregnancy or with a history of neural tube defects or folate related pregnancy complications, MTHFD1 testing can add nuance to decisions on folate and choline intake alongside standard folate recommendations.
• Unexplained homocysteine or folate patterns: When homocysteine, folate, or methylation markers do not fully align with diet and supplementation, MTHFD1 genotyping alongside MTHFR, MTR, MTRR, DHFR, and choline intake review can clarify how your one carbon system is balanced.
• Cardiovascular and cancer risk profiling: In comprehensive preventive assessments, MTHFD1 testing plus methylation and cardiometabolic markers can contribute to a more detailed picture of how one carbon metabolism may interact with long term risk, always interpreted alongside established risk factors.
• Deep methylation and nutrient mapping: For individuals investing in detailed methylation and nutrient testing, MTHFD1 genotyping helps map how folate and choline pathways intersect, guiding personalised support that can be tracked over time.