Can the MTHFD1 rs2236225 AA genotype reduce folate-cycle efficiency and affect red-cell maturation?

The MTHFD1 gene plays a critical role in the cytosolic one-carbon folate cycle, which is essential for cellular division and red blood cell maturation.

Mechanistic pathway of MTHFD1 rs2236225

• Enzymatic destabilization: The MTHFD1 rs2236225 (G1958A) polymorphism causes an Arg653Gln amino acid substitution in the 10-formyl-THF synthetase domain. This change significantly reduces the enzyme's structural stability, half-life, and metabolic efficiency.
• Impaired nucleotide synthesis: Compromised C1-THF synthase activity limits the generation of 10-formyl-THF and 5,10-methylene-THF, which are essential one-carbon donors for de novo purine and thymidylate (dTMP) synthesis, respectively.
• Folate-independent disruption: Because this is a localized pathway inefficiency rather than a systemic deficiency, the restriction in nucleotide synthesis can persist even when serum folate levels are clinically optimal.
• Alternative methyl donor demand: Due to reduced cytosolic folate-cycle flux, carriers of the AA genotype exhibit an increased sensitivity to choline deficiency and a higher reliance on dietary choline as an alternative methyl donor.

Hematological implications

• Erythroid replication stress: Rapidly dividing erythroid progenitors in the bone marrow require a continuous supply of nucleotides. Impaired purine and pyrimidine synthesis induces DNA replication stress during erythropoiesis.
• Abnormal red-cell maturation: This replication block halts normal cell division, leading to macrocytosis and megaloblastic anemia. Clinically, carrying the AA risk genotype is associated with a higher risk of macrocytosis, particularly under conditions of metabolic stress.

Bottom line

• The MTHFD1 rs2236225 AA genotype compromises the structural stability of C1-THF synthase, restricting de novo nucleotide synthesis and impairing normal red-cell maturation (macrocytosis) independently of systemic folate status.