rs7385804 — TFR2

TFR2 rs7385804 — The Hepatic Iron Sensor and Transferrin Saturation Variant

Transferrin receptor 2 (TFR2) is expressed primarily in the liver, where it acts as a sensor of circulating iron — specifically, iron bound to transferrin (the blood's iron transport protein). Unlike its well-known relative TFR1, which regulates cellular iron uptake across many tissues, TFR2 in hepatocytes functions as a surveillance protein: it detects when transferrin saturation rises and signals upstream to increase hepcidin¹¹ hepcidin
A liver-derived peptide hormone that is the master regulator of systemic iron homeostasis; it blocks iron release from the gut and from macrophages production — the body's primary brake on iron absorption. rs7385804 is an intronic variant in TFR2 that tags altered expression or splicing of this receptor, and it has emerged as one of the genome-wide-significant loci for serum iron and transferrin saturation across studies of up to 48,972 participants.

The Mechanism

TFR2 sits at the intersection of two iron-sensing pathways. In hepatocytes, it forms a complex with the HFE protein (the hereditary hemochromatosis gene product) and with hemojuvelin²² hemojuvelin
BMP co-receptor HJV/RGMC, which amplifies BMP-SMAD signaling to hepcidin to amplify BMP-SMAD pathway signaling toward hepcidin transcription. When transferrin saturation is high, diferric transferrin stabilizes TFR2 on the cell surface and sustains hepcidin production; when iron falls, TFR2 is rapidly internalized and degraded, releasing the brake. rs7385804 lies in an intron of TFR2 and appears to function as a regulatory variant or expression quantitative trait locus (eQTL): the C allele is associated with lower TFR2-mediated iron sensing, resulting in measurably lower transferrin saturation and serum iron levels compared to the A allele in multiple large population studies.

The variant does not alter the TFR2 protein sequence directly — it is classified as an intron variant — suggesting its effect is mediated through altered splicing efficiency or transcriptional regulation of TFR2 in hepatic tissue, where expression is strongly restricted. In red blood cell precursors, TFR2 also partners with the erythropoietin receptor to fine-tune erythropoiesis, explaining why rs7385804 also associates with erythrocyte indices (MCH, MCV, red cell count) in large blood cell trait GWAS.

The Evidence

The TFR2 locus surrounding rs7385804 was first identified in a major GWAS of iron homeostasis markers: Benyamin et al. 2014³³ Benyamin et al. 2014
Nature Communications — GWAS of up to 48,972 subjects; TFR2 among 11 genome-wide-significant loci for serum iron and transferrin saturation; SNPs at TFR2 also modify iron markers in HFE C282Y homozygotes. Notably, TFR2 locus variants modulated iron markers specifically in individuals already at risk for hemochromatosis, indicating that TFR2 variation is most consequential when the iron-sensing pathway is already under strain.

The association with red cell indices was demonstrated in the large-scale UK Biobank analysis: Astle et al. 2016⁴⁴ Astle et al. 2016
Cell — 173,480 European-ancestry participants; rs7385804-A associated with higher MCH (P=3×10⁻¹¹⁶) and MCV, and lower RBC count (P=4×10⁻⁹⁰), consistent with TFR2's dual role in iron sensing and erythropoiesis.

The most comprehensive quantification of the iron-status effect came from a meta-analysis of 246,139 participants across Iceland, the UK, and Denmark: Bell et al. 2021⁵⁵ Bell et al. 2021
Communications Biology — rs7385804-C associated with 0.057 SD lower serum iron (P=9×10⁻⁴³) and 0.062 SD lower transferrin saturation (P=3×10⁻³⁹). These effect sizes are modest at the individual level but reflect the consistent, population-wide influence of TFR2 on iron regulation.

In a Chinese study of 2,139 elderly women, An et al. 2012⁶⁶ An et al. 2012
Human Molecular Genetics — rs7385804 associated with reduced serum iron, transferrin, and transferrin saturation, though not with overt iron-deficiency anemia risk, underscoring that this variant modulates iron status continuously rather than acting as a dichotomous disease switch.

Practical Actions

For carriers of the CC genotype, the primary implication is a modestly lower set point for transferrin saturation. This is unlikely to cause symptomatic iron deficiency in well-nourished individuals, but it can shift baseline iron biomarkers into the lower-normal range and make recovery from iron-depleting events (heavy heavy periods, blood donation, intense athletic training) slower. Periodic monitoring of serum ferritin and transferrin saturation — rather than hemoglobin alone — is the most informative approach, since this variant acts upstream of the point where anemia develops. Dietary iron should emphasize heme iron sources (red meat, shellfish) for their superior bioavailability and the preference for consuming vitamin C alongside plant iron sources to maximise non-heme absorption.

For the AA majority, this variant is reassuring: a higher iron set point means the TFR2 iron-sensing arm is functioning at full capacity. Standard monitoring is appropriate.

Interactions

TFR2 variation interacts with HFE C282Y (rs1800562) in a clinically important way: variants at the TFR2 locus were shown to modify iron markers specifically in HFE C282Y homozygotes — the at-risk group for hereditary hemochromatosis. This suggests that TFR2 rs7385804 genotype may modulate the penetrance of HFE-driven iron overload, potentially explaining some of the clinical variability among C282Y homozygotes who range from asymptomatic to severe organ disease. The compound genetic effects of HFE, TFR2, TF (transferrin), and HJV have been documented in a case report of a Thai family with compounded iron dysregulation spanning from chronic anemia to motor neuron disorder (PMID 32895881). TMPRSS6 rs855791 (the TMPRSS6 Ala736Val variant) acts in the same hepcidin-regulation pathway and is the stronger genetic determinant of iron-deficiency anemia risk; cc genotypes of rs7385804 may compound mildly with TMPRSS6 risk alleles in iron-deficient individuals.