rs3761847 — TRAF1

Intronic GWAS variant in the TRAF1-C5 locus on chromosome 9 robustly associated with seropositive rheumatoid arthritis risk

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TRAF1-C5 — The Inflammatory Signal Amplifier at Chromosome 9q33

Deep within the long arm of chromosome 9 sits a genetic locus that helps explain why rheumatoid arthritis clusters in families and why some patients respond poorly to the most effective treatments available. The TRAF1-C5 locus11 The TRAF1-C5 locus
TRAF1 encodes TNF receptor-associated factor 1, a scaffold protein inside immune cells that amplifies inflammatory NF-kB signaling; C5 encodes complement component 5, a protein that drives joint inflammation through the complement cascade at 9q33.3 contains two genes, each contributing to the inflammatory cascade that erodes joints in autoimmune arthritis. rs3761847 is an intronic variant in TRAF1 that serves as the principal GWAS tag SNP for this entire locus — its G allele marks a chromosomal haplotype that increases susceptibility to rheumatoid arthritis by approximately 32% per copy.

The Mechanism

rs3761847 sits in an intron of TRAF1 on chromosome 9 (GRCh38 position 120,927,961), with the TRAF1 gene encoded on the minus strand. The variant itself is not a coding change — it does not alter any amino acid. Instead, it acts as a linkage disequilibrium tag22 linkage disequilibrium tag
A tag SNP marks a haplotype block: it travels with nearby functional variants through generations because recombination between them is rare, making the tag SNP a reliable proxy for the causal variant(s) for a haplotype.

TRAF1 protein is a key intracellular scaffold in the TNF receptor signaling pathway. When TNF-alpha binds its receptor on immune cells, TRAF1 is recruited to the receptor complex and modulates the downstream activation of NF-kB33 NF-kB
Nuclear factor kappa-light-chain-enhancer of activated B cells — a master transcription factor that switches on hundreds of pro-inflammatory genes including cytokines, chemokines, and adhesion molecules that drive joint inflammation.

The neighboring C5 gene contributes through a separate mechanism: complement component 5 is cleaved to C5a in the synovial fluid of inflamed joints, where it drives macrophage activation and inflammatory cytokine release.

The Evidence

The foundational discovery came from Plenge et al. (2007)44 Plenge et al. (2007)
NEJM genome-wide study analyzing 317,503 SNPs in 1,522 anti-CCP-positive RA cases and 1,850 controls from NARAC and EIRA cohorts, replicated in an additional 997 cases and 1,777 controls, who identified rs3761847 as the top signal at the TRAF1-C5 locus with an odds ratio of 1.32 (95% CI 1.23–1.42, p = 4×10⁻¹⁴) in anti-CCP-positive rheumatoid arthritis — one of the most significant non-HLA genetic associations for RA at that time. Crucially, the effect was strongest in seropositive (anti-CCP-positive) disease, which is the most genetically driven, erosive form of RA.

A meta-analysis by Song et al. (2014)55 meta-analysis by Song et al. (2014)
Immunological Investigations meta-analysis encompassing 24 studies with 22,682 RA cases and 23,493 controls across European and Asian populations confirmed the European association (OR 1.156, 95% CI 1.006–1.327 per G allele) while finding no statistically significant effect in Asian cohorts (OR 1.049, p = 0.333). This ethnic divergence is explained by differences in linkage disequilibrium66 linkage disequilibrium
LD refers to the non-random co-inheritance of alleles; if the causal variant is in strong LD with rs3761847 in Europeans (r²=0.67) but weaker LD in Asians (r²=0.37), the tag SNP is more informative in the former between rs3761847 and the actual functional variant(s) in the two population groups.

Beyond susceptibility, the TRAF1-C5 locus influences treatment outcomes. Canhão et al. (2015)77 Canhão et al. (2015)
Biomedical Research International, Southern European RA patients on anti-TNF therapy found that the G risk allele at rs3761847 predicted poor response to anti-TNF biologics in multivariate analyses.

Practical Actions

For G-allele carriers — particularly GG homozygotes — the key clinical implications are threefold: early awareness of seropositive RA symptoms, proactive monitoring of relevant biomarkers (anti-CCP antibodies and CRP), and awareness that standard anti-TNF biologic therapy may be less effective for GG carriers. These individuals may benefit from JAK inhibitors or IL-6 pathway inhibitors as preferential first-line biologic options when conventional DMARDs fail.

The G allele is approximately 43% globally and 42% in Europeans, making it common rather than rare. Most Europeans carry at least one copy. GG homozygotes (~18% in Europeans) carry the highest genetic burden at this locus. Seronegative RA patients should note that the evidence for this locus is substantially weaker outside the anti-CCP-positive disease subtype.

Interactions

rs3761847 sits in a pathway heavily influenced by other autoimmune susceptibility loci. The TNFAIP3 locus on chromosome 6q23 — specifically rs6920220 and rs13207033 — encodes A20, the primary brake on NF-kB signaling that TRAF1 activates. The PTPN22 rs2476601 variant (R620W) represents a third independent RA risk signal that alters T-cell receptor signaling thresholds.

Genotype Interpretations

What each possible genotype means for this variant.

AA Non-Risk Genotype Normal

Two copies of the common A allele — no increased TRAF1-C5 risk

You carry two copies of the A allele at rs3761847, the non-risk genotype at the TRAF1-C5 locus. Approximately 28% of people globally share this genotype (33% in Europeans). GWAS studies show no increased rheumatoid arthritis susceptibility from the A allele — your genetic risk from this locus specifically is at or below average population levels.

AG One Risk Allele Intermediate

One G risk allele — moderately elevated TRAF1-C5 RA susceptibility

Having one G allele at rs3761847 places you in the most common risk category for this locus. The TRAF1-C5 association is driven primarily by the seropositive (anti-CCP and/or RF positive) form of rheumatoid arthritis — the most destructive and genetically influenced subtype. Your lifetime baseline risk of RA (~1% in the general population) is modestly elevated by this allele, with an OR of approximately 1.32 per G allele from the original Plenge et al. NEJM discovery study.

Early symptoms of seropositive RA include symmetric joint stiffness lasting more than 30 minutes in the morning, swelling in small joints of the hands and feet, fatigue, and occasional low-grade fever. Identifying elevated anti-CCP antibodies before clinical symptoms develop is the most actionable early warning.

GG Homozygous Risk High Risk

Two G risk alleles — highest TRAF1-C5 RA susceptibility, and reduced anti-TNF response

GG homozygosity at rs3761847 represents the highest genetic burden at the TRAF1-C5 locus.

This variant does not guarantee RA — lifetime risk remains well under 10% even in GG carriers. But combined with HLA-DRB1 shared epitope alleles, PTPN22 R620W (rs2476601), and anti-CCP seropositivity, GG at rs3761847 is part of the highest-risk RA profile characterized in the literature.