Is the MTRR rs1801394 GG genotype associated with higher homocysteine?

The MTRR gene encodes methionine synthase reductase, a crucial enzyme responsible for maintaining methionine synthase in its active state. The rs1801394 genetic variant is widely studied for its influence on the human methyl-group pathway and sulfur amino acid metabolism.

Mechanistic pathway

• Enzymatic alteration: The MTRR rs1801394 GG genotype involves a missense A→G transition, resulting in an isoleucine-to-methionine substitution (Ile22Met) within the enzyme's FMN-binding domain.
• Reduced catalytic activity: This structural modification weakens the binding and interaction between MTRR and methionine synthase (MTR).
• Impaired remethylation: Because MTRR is less efficient at regenerating active methylcobalamin (vitamin B12), the vital conversion rate of homocysteine to methionine is significantly slowed, altering overall metabolic flow.

Clinical evidence

• Context-dependent baseline levels: Population studies evaluating the direct correlation between the GG genotype and baseline plasma homocysteine levels demonstrate inconsistent or neutral findings when analyzed in isolation.
• Nutritional and genetic synergy: Elevated baseline homocysteine is highly plausible and clinically observable when the GG genotype co-occurs with suboptimal B-vitamin status (specifically folate and vitamin B12) or other folate-pathway mutations, such as the MTHFR C677T variant, which compound the biochemical bottleneck.

Bottom line

• The MTRR rs1801394 GG genotype directly compromises MTRR enzymatic efficiency and alters homocysteine-to-methionine remethylation; however, its clinical manifestation as elevated plasma homocysteine is highly dependent on concurrent B-vitamin deficiencies or compounding folate-pathway mutations.