rs10818488 — TRAF1 TRAF1-C5 rheumatoid arthritis variant

Intergenic regulatory variant between TRAF1 and C5 on chromosome 9; the A allele reduces TRAF1 expression, amplifying NF-kB-driven inflammation and increasing rheumatoid arthritis risk in Europeans

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TRAF1-C5 — The Signal Between Two Inflammatory Sentinels

Two genes sit on chromosome 9q33-34, separated by roughly 10 kilobases of intergenic DNA: TRAF1, a signaling adapter that modulates NF-kB activation, and C5, the complement protein that bridges innate and adaptive immunity. The rs10818488 polymorphism lies exactly in this gap — a regulatory SNP11 SNP
Single nucleotide polymorphism — a single-letter DNA difference that varies between people that is one of the most robust and well-replicated non-HLA risk loci for rheumatoid arthritis (RA) identified to date. The A allele, carried by approximately 42% of Europeans, confers measurably elevated RA risk and is associated with faster joint destruction in established disease.

The Mechanism

rs10818488 maps to the intergenic region approximately 10 kb from both the TRAF1 and C5 transcription start sites. It does not change any protein directly. Instead, it alters the local regulatory landscape: the A allele creates a binding site for EP30022 A allele creates a binding site for EP300
EP300 is a histone acetyltransferase that opens chromatin and activates transcription; binding at this locus appears to alter TRAF1 expression levels in immune cells, a histone acetyltransferase that remodels chromatin and activates transcription. Experimental evidence from monocytes confirms the functional direction: carriers of risk alleles at this locus express less TRAF1 protein33 less TRAF1 protein
Paradoxically, reduced TRAF1 expression leads to more inflammation because TRAF1 normally sequesters LUBAC, the linear ubiquitin assembly complex; without sufficient TRAF1, LUBAC is released and drives stronger NF-kB activation upon stimulation and produce increased amounts of TNF and IL-6. TRAF1's role in NF-kB regulation is paradoxical: while it amplifies survival signaling through TNFR family members, it also suppresses excessive TLR/NLR responses by sequestering LUBAC. Lower TRAF1 expression tips this balance toward enhanced inflammatory cytokine output.

This creates a self-reinforcing loop in RA pathogenesis: reduced TRAF1 expression → amplified TNF production → further joint inflammation → progressive erosive disease. The A allele's association with radiographic damage progression reflects exactly this mechanism.

The Evidence

The TRAF1-C5 locus was first established as an RA risk locus by Plenge et al. in the New England Journal of Medicine44 Plenge et al. in the New England Journal of Medicine
A landmark 2007 genome-wide association study with stepwise replication across Dutch, Swedish, and US cohorts (2007), with rs10818488 confirmed across 2,719 RA patients and 1,999 controls (OR 1.28, 95% CI 1.17–1.39, p = 1.40×10⁻⁸). The population-attributable risk — the fraction of RA cases attributable to this variant — was 6.1%, making it one of the most consequential non-HLA loci. A candidate gene study55 candidate gene study
Using targeted genotyping of biologically plausible genes rather than genome-wide scanning replicated the finding across four independent sample sets: the A allele gave an OR of 1.26 overall, with AA homozygotes showing OR 2.06 (95% CI 1.42–2.98) compared with GG carriers.

A meta-analysis of 24 studies66 meta-analysis of 24 studies
Pooling 22,682 RA cases and 23,493 controls confirmed the association in Europeans (OR 1.229, 95% CI 1.094–1.381, p=0.001) but not significantly in Asians, where the directional effect is reversed in some analyses — a genuine genetic heterogeneity reflecting different LD patterns at this locus across ancestries. An updated meta-analysis77 updated meta-analysis
21 studies, 15,171 cases and 13,998 controls, with population-stratified analysis found the G allele is paradoxically protective in Europeans but a weak risk allele in Asians, consistent with the A allele's European-ancestry risk direction.

Beyond susceptibility, the A allele is associated with disease severity: carriers show greater radiographic joint damage progression over time (p=0.008). Association with higher disease activity scores has been replicated in Middle Eastern populations. The variant also extends to systemic lupus erythematosus, with an OR of 1.21 (95% CI 1.12–1.31, p=5.0×10⁻⁶) in Europeans in a separate meta-analysis88 a separate meta-analysis.

Practical Actions

For AA homozygotes carrying two copies of the risk allele, the priority is early recognition of RA symptoms and baseline autoantibody testing — anti-CCP (ACPA) and rheumatoid factor — since the A allele's risk is predominantly expressed in seropositive, erosive RA. Joint stiffness lasting over 30 minutes in the morning, symmetric swelling of small hand joints, and unexplained fatigue are the key early warning signs. Because this locus also influences response to anti-TNF biologics (rs3761847, a nearby proxy SNP at the same locus, predicts anti-TNF outcomes), genotype information from this region may eventually guide biologic selection.

For the heterozygous AG genotype, the modestly elevated risk warrants awareness rather than aggressive clinical action, unless compounded by HLA-DRB1 shared epitope alleles or PTPN22 R620W carriage.

Interactions

rs10818488 and rs3761847 are the two most studied SNPs at the TRAF1-C5 locus, located approximately 10 kb apart in the same intergenic haplotype block. In most populations they are in high linkage disequilibrium and tag the same risk haplotype. The nearby rs3761847 G allele has been associated with poor response to anti-TNF therapy in RA, while rs10818488 A allele captures the overall susceptibility signal. Carrying risk alleles at both SNPs likely identifies the highest-risk individuals at this locus.

PTPN22 rs2476601 (R620W) is the strongest non-HLA non-TRAF1 RA susceptibility variant; combined carriage of PTPN22 A allele and TRAF1-C5 A allele substantially elevates RA risk beyond either alone through independent immune signaling pathways (T-cell signaling threshold versus NF-kB regulation). TNFAIP3 rs13207033, a protective NF-kB regulatory variant at the 6q23 locus, may partially offset TRAF1-C5 risk through independent A20-mediated NF-kB suppression.

Genotype Interpretations

What each possible genotype means for this variant.

GG Typical TRAF1 Regulation Normal

Low-risk genotype at the TRAF1-C5 locus; normal NF-kB regulatory capacity

You carry two copies of the G allele at rs10818488, the low-risk genotype at the TRAF1-C5 locus. Approximately 34% of people of European descent share this genotype. Your TRAF1 expression capacity at this locus is not compromised by the A allele regulatory variant; NF-kB signaling in your immune cells is regulated at a baseline level. This is the most favorable genotype at this locus for rheumatoid arthritis and systemic lupus erythematosus susceptibility.

AG One Risk Allele Intermediate

One copy of the A risk allele — modestly elevated RA risk through reduced TRAF1 expression

The heterozygous AG genotype represents the most common risk configuration at this locus in Europeans. The per-allele OR of approximately 1.26 translates to a moderate increase in lifetime RA risk, particularly when combined with HLA-DRB1 shared epitope alleles or PTPN22 R620W (rs2476601). Seropositive RA — defined by positive anti-CCP or rheumatoid factor — is the subtype most strongly driven by TRAF1-C5 variants. Seronegative RA has a weaker genetic signal at this locus.

The A allele has also been associated with more radiographic joint damage progression in established RA, suggesting it may influence disease severity in addition to susceptibility. This makes early diagnosis particularly valuable for A-allele carriers who do develop RA.

AA Two Risk Alleles High Risk

Two copies of the A risk allele — substantially elevated RA susceptibility and radiographic progression risk

The AA homozygous genotype at rs10818488 carries the strongest risk at the TRAF1-C5 locus. This regulatory variant sits in the intergenic region approximately 10 kb from TRAF1, creating an EP300 histone acetyltransferase binding site on both chromosomes. Functional studies in monocytes confirm that risk-allele carriers express less TRAF1 protein and produce higher levels of TNF and IL-6 in response to stimulation. The net effect is a lower inflammatory threshold and reduced capacity to self-terminate NF-kB signaling cascades.

The A allele's risk is predominantly expressed in ACPA-positive (anti-CCP seropositive) RA — the subtype associated with bone erosion, joint destruction, and disability. ACPA-negative RA has a weaker genetic signal at TRAF1-C5. The link to faster radiographic progression means that once joint disease begins in AA carriers, disease control is more urgent than for GG carriers.

This locus may also influence treatment response: nearby rs3761847 (in high LD with rs10818488) has been associated with poor anti-TNF biologic response, suggesting the TRAF1-C5 haplotype may eventually guide biologic selection decisions in clinical rheumatology.