MTHFD1 rs2236225: What Your Genotype Means
The rs2236225 polymorphism is a common genetic change in the MTHFD1 gene, historically known as G1958A or the R653Q variant. It subtly decreases the enzymatic stability of a key trifunctional enzyme involved in one-carbon folate metabolism. As a result, carrying this variant is associated with altered folate and choline handling and a modestly increased maternal risk for neural tube defects when dietary nutrient levels are insufficient.
What each genotype means
Typical enzyme stability
You carry two copies of the common G allele, corresponding to the typical arginine (R) amino acid at position 653 (c.1958G/G). Research indicates this genotype confers standard MTHFD1 enzyme stability and baseline one-carbon metabolic flux without the increased maternal risk for neural tube defects or heightened sensitivity to low dietary choline seen with the variant allele.
Carried by approximately 35% to 40% of individuals of European ancestry, and generally more common across African and East Asian populations.
Moderately reduced enzyme stability
You carry one copy of the A variant allele (c.1958G>A, p.Arg653Gln). Clinical studies suggest this causes a moderate reduction in MTHFD1 synthetase stability and can moderately increase metabolic reliance on dietary choline for methyl donation, especially under low-folate conditions. Evidence regarding clinical risk for maternal neural tube defects remains mixed and limited for heterozygous carriers.
Carried by roughly 45% to 50% of people of European descent; less common in East Asian populations.
Reduced enzyme stability
You carry two copies of the A variant allele, historically designated as 1958AA or the 653QQ genotype. Published nutritional research links this genotype with reduced stability of the trifunctional MTHFD1 enzyme, resulting in a higher sensitivity to low dietary choline and an elevated maternal risk for neural tube defects when folate intake is marginal. These findings represent population associations and evidence remains limited, so dietary requirements should be discussed with a qualified healthcare professional.
Carried by roughly 15% to 20% of individuals of European ancestry, but is significantly rarer in East Asian and African populations.
Understanding rs2236225 and the MTHFD1 Gene
The single nucleotide polymorphism rs2236225 is situated within exon 21 of the MTHFD1 gene, mapped to chromosome 14. This variant represents a guanine-to-adenine substitution (c.1958G>A) that leads to an amino acid substitution from arginine to glutamine at codon 653 (p.Arg653Gln, often termed R653Q). The MTHFD1 gene encodes a critical cytoplasmic trifunctional enzyme that possesses methylenetetrahydrofolate dehydrogenase, methenyltetrahydrofolate cyclohydrolase, and 10-formyltetrahydrofolate synthetase enzymatic activities. The R653Q substitution falls within the synthetase domain, rendering the folded enzyme somewhat more thermolabile and prone to accelerated degradation compared to the canonical enzyme. Because this enzyme directs the movement of single-carbon units toward either purine synthesis or homocysteine remethylation, shifts in its stability alter the baseline efficiency of cellular methylation reactions.
Nutrigenomics: The Folate and Choline Interplay
One-carbon metabolism is an interconnected biochemical highway essential for synthesizing nucleotides and maintaining DNA methylation. Under ordinary circumstances, MTHFD1 supplies intermediate folate derivatives needed to maintain the methionine cycle. When MTHFD1 synthetase function is impaired due to the rs2236225 variant, cells experience a bottleneck in de novo methionine synthesis. To compensate for reduced folate flow, the metabolic network places heavier reliance on the alternative, betaine-dependent remethylation pathway, which utilizes choline as a methyl donor. Research demonstrates that individuals carrying the variant allele, particularly homozygotes, display elevated plasma homocysteine levels under experimental folate-restricted conditions. Consequently, rs2236225 represents a classic nutrigenomics candidate where genetic variation modulates the functional biological demand for essential dietary nutrients.
Clinical Evidence and Developmental Risks
The primary clinical focus on rs2236225 centers on maternal risk for fetal structural anomalies, specifically neural tube defects (NTDs) and congenital heart disease. Case-control studies have identified a statistically significant overrepresentation of the maternal AA (QQ) genotype among mothers of affected offspring. However, evidence strength remains classified as limited to moderate across broad scientific literature because replication studies in varied ethnic cohorts have generated mixed results. The observed risk increase is relative, not absolute, meaning that most mothers carrying the variant have uncomplicated pregnancies and healthy infants. The risk appears to be heavily contingent on nutritional context; adequate peri-conceptional folate and choline status largely mitigates the enzymatic liability conferred by the polymorphism.
Population Distribution and Genotype Patterns
The rs2236225 variant is widespread rather than a rare mutation. The minor A allele is particularly prevalent in European populations, carrying an allele frequency near 0.40 to 0.43, meaning that well over half of individuals of European ancestry possess at least one copy. In contrast, the A allele appears less frequently among individuals of African or East Asian ancestry, where minor allele frequencies typically range between 0.15 and 0.25. Because these variations are common worldwide, harboring the A allele represents normal human diversity rather than a disease state. Its high prevalence reinforces that dietary availability of cofactors and nutrients plays a decisive role in whether the metabolic liability manifests clinically.
Translating Your Genotype: What You Can and Cannot Do
Learning your rs2236225 genotype provides biochemical context, but it does not diagnose any illness, predict unavoidable birth defects, or indicate nutrient deficiency on its own. Genetic results are probabilistic tendencies that must be integrated with clinical status, diet, and laboratory tests like serum folate and total homocysteine. Individuals planning a pregnancy or seeking to support their one-carbon metabolism can ensure steady dietary intake of folate from dark leafy greens and legumes alongside dietary choline found in eggs, fish, and cruciferous vegetables. Anyone considering targeted supplementation, high-dose vitamins, or adjusting medication should discuss options directly with a registered dietitian, genetic counselor, or primary care clinician.
How common is this variant?
The minor A allele occurs at a frequency of approximately 0.40 to 0.43 in European ancestries, with roughly 15-20% of individuals carrying the homozygous AA genotype. The variant is less common in East Asian and African populations, where the A allele frequency ranges from 0.15 to 0.25.
Frequently asked questions
Does carrying the rs2236225 A allele mean my baby will have a birth defect?
No. The presence of the A allele is associated with a modest relative increase in risk, but the absolute likelihood of a neural tube defect remains very low. Most women carrying this variant have healthy pregnancies, particularly when maintaining standard recommended intake of prenatal nutrients.
Is MTHFD1 the same thing as the MTHFR gene?
No, they are distinct enzymes operating at different points within one-carbon metabolism. While MTHFR converts 5,10-methylenetetrahydrofolate into 5-methyltetrahydrofolate, MTHFD1 regulates intermediate steps between formate, THF, and nucleotide synthesis.
Should I take high-dose supplements if I have the AA genotype?
Not necessarily, as excessively high doses of isolated vitamins are not always beneficial and can occasionally dysregulate pathway dynamics. A balanced approach focusing on standard dietary sources of folate and choline is typically recommended, and any high-dose supplementation should be evaluated with your doctor.
Can a genetic test determine if I have a choline deficiency?
No. A genetic variant points to potential metabolic vulnerabilities and nutrient handling tendencies, but cannot measure nutrient levels. Choline status is influenced by daily dietary intake, digestive absorption, and overall metabolic requirements.
Sources & further reading
Educational information only, last refreshed 9/10/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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