Methylation enzyme variant
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About rs1801133 (MTHFR)
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About rs1801133 (MTHFR)
Overview and History
rs1801133 is a single-nucleotide polymorphism (SNP) in the MTHFR gene, often reported as the C677T change and resulting in an alanine-to-valine substitution in the enzyme. It is classified as a functional genetic variant that can alter MTHFR enzyme stability and activity in many populations.
The MTHFR enzyme converts 5,10-methylene-tetrahydrofolate to 5-methyl-THF, the primary circulating form of folate used for remethylation of homocysteine to methionine and for providing methyl groups for DNA and biochemical methylation. Because it sits at the center of one-carbon metabolism, variants at rs1801133 have been widely studied for their effects on folate distribution, homocysteine levels, and methylation capacity across different nutritional contexts.
Interpreting Highs and Lows
Genetic variants at rs1801133 are reported as genotypes (commonly CC, CT, or TT) that correlate with typical, intermediate, or reduced MTHFR enzyme activity. Genotypes associated with reduced activity are often linked with higher circulating homocysteine and altered proportions of folate forms, while genotypes associated with typical activity show expected folate distribution in the same context. Interpretation should always use the full Nutrient Zoomer panel—combining genotype with measured folate species, B12, and homocysteine provides a clearer picture than the genetic result alone.
Featured Test
Nutrient Zoomer includes rs1801133 to connect inherited methylation capacity with measured nutrient markers. This variant helps explain why folate, B12, and homocysteine values may differ between individuals and supports personalized interpretation of one‑carbon metabolism and methylation-related nutrient demand.
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Mary Beth Augustine
DCN, RDN, FAND- Lead Clinical Educator
Suzanne Barker
MS, RDN, LD, CTTS, CGP- Clinical Educator
Suzette Garcia
MSc- MHNE- Clinical Educator
Brooke Mader Ganev
MS, CNS, LDN, FDN- Clinical Educator
Adair Anderson
MS, RDN, LDN- Clinical Educator
Lillie Luu Nguyen
DCN, CNS, LDN- Clinical Educator
Jason Barker
ND- Clinical Educator
Emaline Brown
ND- Clinical Educator
Dana Filatova
DCN, CNS, LDN- Clinical Educator
Jessy Dhanjal
ND- Clinical Educator
Nour Amri
MS, LDN, CNS, CKNS- Clinical Educator
