SLC19A1 rs1051266: What Your Genotype Means
The genetic variant rs1051266 is a widely studied missense single-nucleotide polymorphism located in the SLC19A1 gene, also historically designated as reduced folate carrier 1 (RFC1 80G>A). It results in an amino acid substitution of arginine to histidine at position 27 (Arg27His), subtly altering the kinetics of cellular folate uptake. Observational research links this variant to small differences in circulating folate levels, homocysteine balance, and altered cellular transport of antifolate medications such as methotrexate.
What each genotype means
Standard folate transport kinetics
This genotype is often referred to in literature as the wild-type or reference state for the SLC19A1 gene. Research suggests that individuals with this genotype may exhibit different cellular uptake rates for folates and antifolate medications like methotrexate compared to those carrying the A allele. Please discuss any concerns regarding medication response or nutritional status with your clinician or pharmacist.
Carried by roughly 25-35% of individuals in many European and East Asian populations.
Altered folate transport profile
This heterozygous genotype involves one copy of the common G allele and one copy of the A allele, which results in an Arg27His amino acid substitution. Some studies suggest this variant may influence red blood cell folate concentrations and the cellular uptake of certain medications, though findings are mixed across different clinical cohorts. Always consult with your healthcare provider before making changes to your diet or medication regimen.
This is a very common genotype, found in approximately 40-50% of individuals across many global populations.
Variant folate transport profile
Carrying two copies of the A allele is associated with altered kinetics of the reduced folate carrier protein. Research has explored links between this genotype and variations in folate levels or responses to antifolate drugs, but results remain inconsistent across different studies and ancestries. If you are prescribed medications that interact with folate pathways, please discuss your specific genetic profile with your clinician or pharmacist.
Carried by roughly 20-30% of individuals in many European and East Asian populations.
Understanding the Variant: SLC19A1 rs1051266
The single-nucleotide polymorphism rs1051266 is located in exon 2 of the SLC19A1 gene on chromosome 21. In scientific literature, it is frequently documented by its cDNA coordinate c.80G>A or its protein alteration p.Arg27His. At this specific genomic position, the nucleotide can exist as either a guanine (G) or an adenine (A). Because it is a missense alteration, the nucleotide change swaps an arginine residue for a histidine residue in the amino-terminal cytoplasmic tail of the resulting transporter protein. This structural change modifies the transport kinetics across cell membranes, influencing the efficiency with which folates and antifolate analogs enter peripheral cells. While it represents one of the most widely genotyped variants within nutrigenomics, its functional consequences are subtle and represent normal human biological variation rather than a pathogenic disruption.
The Biological Role of the Reduced Folate Carrier
The SLC19A1 gene encodes the solute carrier family 19 member 1 protein, more commonly referred to as the reduced folate carrier 1 (RFC1). RFC1 is an essential transmembrane protein that operates as an anion exchanger, delivering 5-methyltetrahydrofolate—the primary circulating form of dietary and supplemental folate—into cells throughout the body. Folates are indispensable coenzymes required for one-carbon metabolism, nucleotide synthesis, cellular proliferation, and the remethylation of homocysteine to methionine. In addition to physiological folates, the reduced folate carrier serves as the primary gateway for cellular internalization of hydrophilic antifolate drugs, most notably methotrexate. Alterations in RFC1 transporter efficiency can therefore influence not only cellular nutrient status but also intracellular drug accumulation in tissues.
Evaluating Research and Evidence Strength
Evidence evaluating rs1051266 is classified as limited to moderate across clinical literature. Numerous observational studies have investigated whether the G and A alleles create meaningful differences in human health outcomes. Some clinical cohorts report that individuals carrying the G allele (or the GG genotype) have modest differences in red blood cell folate or plasma folate concentrations relative to AA homozygotes, alongside minor shifts in plasma homocysteine. Other pharmacogenetic investigations indicate that the variant modulates methotrexate uptake and clearance kinetics, with conflicting reports associating specific alleles with toxicity or therapeutic response. However, meta-analyses frequently reveal modest effect sizes and inconsistent findings across heterogeneous populations. Major pharmacogenomic guidelines such as CPIC do not mandate clinical dosing changes based on rs1051266 alone, underscoring that its clinical impact remains non-deterministic.
Population Diversity and Allele Frequencies
The rs1051266 variant is remarkably common across global human populations, indicating that neither allele confers a severe evolutionary disadvantage. Large-scale genomic databases, such as gnomAD and the 1000 Genomes Project, demonstrate that both the G and A alleles are balanced throughout most ancestral cohorts. The frequency of the G allele typically ranges between 40% and 55% in European, East Asian, and Admixed American populations, while hovering near 40% to 50% in African cohorts. Because both alleles are so evenly distributed, heterozygous individuals (GA) constitute approximately half of many tested populations, while each homozygous group (GG and AA) makes up roughly one-quarter. This widespread distribution confirms that the polymorphism reflects ancestral genetic diversity rather than a rare disease-causing defect.
Practical Implications: What This Means for You
Discovering your rs1051266 genotype provides interesting educational insight into your nutritional biochemistry, but it cannot be used to diagnose a medical condition or predict specific health problems. Carrying an A or G allele does not signify folate deficiency or clinical disease on its own. For overall wellness, standard nutritional guidelines—such as consuming a balanced diet rich in leafy greens, legumes, and fortified whole grains—remain universally effective regardless of your genotype. If you are prescribed medications that utilize the folate pathway, such as methotrexate for rheumatologic or oncologic conditions, you should never alter your dosing, supplement regimen, or prescription schedule based on commercial genetic testing. Always discuss your personal medication plan and laboratory evaluations with your physician or pharmacist.
How common is this variant?
The G allele frequency ranges between roughly 40% and 55% across European, East Asian, and African ancestral groups, making heterozygous and homozygous genotypes common worldwide.
Frequently asked questions
Does having the SLC19A1 rs1051266 variant mean I have a folate deficiency?
No, having one or two copies of this variant does not cause clinical folate deficiency. The polymorphism causes only subtle shifts in transport kinetics, and dietary intake remains the primary determinant of your folate status. Routine blood testing ordered by a physician is the only way to evaluate your actual folate levels.
Should I take high-dose folic acid if I carry the AA genotype?
You should not initiate high-dose vitamin supplementation based solely on an rs1051266 result. Excessive intake of supplemental folic acid can mask vitamin B12 deficiencies and cause other biological imbalances. A standard, balanced diet usually provides adequate folate for individuals carrying this common variant.
How does rs1051266 interact with the MTHFR gene?
SLC19A1 governs how folate is transported into your cells, whereas the MTHFR enzyme converts folate into its active metabolic form inside the cell. While some research explores cumulative interactions between transport and conversion variants, clinical evidence does not support specialized diets or treatment plans based on these combinations.
Does rs1051266 affect how I respond to methotrexate?
Methotrexate relies on the reduced folate carrier encoded by SLC19A1 to enter cells, and some studies suggest rs1051266 may influence drug clearance or side-effect susceptibility. However, evidence is inconsistent, and clinical guidelines do not recommend altering your dose based on this variant. Always consult your prescribing physician or pharmacist before making any changes.
Sources & further reading
Educational information only, last refreshed 9/5/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs1051266?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29