MTRR GENE

MTRR Gene — methionine synthase reductase regenerates active vitamin B12 for the methylation cycle, and MTRR A66G variants reduce this recycling, compounding with MTHFR variants for elevated homocysteine and impaired methylation.

Whole genome sequencing evaluates all MTRR variants alongside the complete methylation pathway — MTHFR, MTR, BHMT, CBS, COMT — providing the network-level methylation assessment that single-gene tests cannot.

MTRR

About this condition

MTRR Gene — Methionine Synthase Reductase

MTRR (methionine synthase reductase, chromosome 5p15.31) regenerates the active form of vitamin B12 (methylcobalamin) required by MTR (methionine synthase) to convert homocysteine to methionine. MTRR A66G (rs1801394) is common — GG homozygotes (~25% of populations) have reduced MTRR activity, potentially impairing B12 recycling.

MTRR A66G alone has modest clinical impact, but it compounds significantly with MTHFR C677T. An individual with MTHFR 677 CT + MTRR 66 GG may have substantially impaired methylation capacity — elevated homocysteine, reduced methylfolate availability — when either variant alone would have minimal effect. This network interaction is why comprehensive methylation testing is superior to single-gene MTHFR testing.

Clinical implications include: supplementation with active B12 (methylcobalamin) rather than inactive cyanocobalamin for MTRR GG individuals, particularly when combined with MTHFR variants; homocysteine monitoring; and pregnancy supplementation optimization (adequate B12 and methylfolate for neural tube defect prevention).

MTRR A66G alone is mild. MTRR A66G + MTHFR C677T together = clinically significant methylation impairment. This is why testing one gene without the other provides incomplete — and potentially misleading — information.

Gene locus: MTRR (5p15.31)

Methylation is a pathway, not a single gene. MTRR must be evaluated alongside MTHFR, MTR, CBS, and COMT for clinically meaningful methylation assessment.

MTRR GG + MTHFR CT compounds for clinically significant homocysteine elevation — network testing reveals true risk

Testing MTHFR alone may show 'heterozygous, mild risk.' Testing MTRR alone may show 'homozygous, mild risk.' Testing both together reveals a compound genotype with clinically significant methylation impairment requiring active B12 and methylfolate supplementation. WGS captures both simultaneously.

Active B12 (methylcobalamin) vs. inactive cyanocobalamin — MTRR genotype guides supplementation form

MTRR GG individuals have reduced capacity to regenerate active B12 from inactive forms. Supplementation with methylcobalamin (pre-activated B12) bypasses the MTRR-dependent activation step. Without MTRR genotyping, patients may supplement with cyanocobalamin that their bodies cannot efficiently activate.

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