Does MTHFD1 rs2236225 AA reduce folate-mediated one-carbon metabolism and increase vulnerability when folate is low?

The MTHFD1 rs2236225 (G1958A) polymorphism represents a significant genetic modifier of metabolic resilience, functioning as a sensitivity allele that directly alters one-carbon pathway capacity.

Molecular mechanisms of metabolic reduction

• Enzymatic instability: The rs2236225 variant causes an arginine-to-glutamine substitution (p.Arg653Gln) in the 10-formyl-THF synthetase domain. While substrate affinity remains normal, this structural change increases thermolability and enhances binding to the E3 ubiquitin ligase TRIM21, accelerating proteasomal degradation and lowering steady-state enzyme levels.
• Reduced metabolic flux: This rapid enzyme turnover results in a 25% to 26% reduction in de novo purine synthesis and impaired formate incorporation into DNA. This restriction shifts metabolic homeostasis, forcing cellular reliance on alternative methyl donors like choline and betaine.

Clinical and physiological vulnerability

• Nutritional interaction: In folate-replete states, individuals with the homozygous AA genotype typically maintain normal homocysteine levels. However, low folate status unmasks this genetic vulnerability.
• Elevated homocysteine and clinical risk: Under dietary folate restriction, the AA genotype impairs homocysteine remethylation, significantly elevating plasma homocysteine levels. This compounded metabolic strain increases developmental and physiological susceptibility, elevating the risk of neural tube defects, compromised sperm quality, and adverse events triggered by environmental stressors like arsenic exposure or low serine/glycine availability.

Bottom line

• The MTHFD1 rs2236225 AA genotype acts as a metabolic sensitivity allele; it does not inherently cause folate deficiency but restricts de novo purine synthesis by 25% and impairs homocysteine remethylation, significantly increasing clinical vulnerability when folate status is low.