rs13190932 — TRAF3IP2 R74W

TRAF3IP2 R74W — The Primary GWAS Signal for Psoriatic Arthritis at the IL-17 Adaptor Locus

The TRAF3IP2 gene encodes Act1 (also called CIKS — Connection to IKK and Stress-activated protein kinase), the essential scaffolding protein¹¹ the essential scaffolding protein
Act1 is recruited to the cytoplasmic domain of the IL-17 receptor upon IL-17A or IL-17F binding, bridging receptor activation to downstream NF-κB and MAP kinase inflammatory signaling in the IL-17 pathway. When genome-wide association studies scanned the locus looking for the single strongest statistical signal for psoriatic arthritis, rs13190932 — encoding the R74W (Arg74Trp) amino acid substitution in Act1 — emerged as the top hit: P = 8.56 × 10⁻¹⁷, odds ratio 1.83 in the combined sample of over 4,700 individuals of European descent. This is one of the most significant non-HLA association signals in psoriatic arthritis genetics.

The Mechanism

R74W changes arginine to tryptophan at position 74 of Act1, located in the N-terminal region of the protein near its TRAF-binding domain. Critically, functional assays show that R74W does not disrupt TRAF6 binding²² R74W does not disrupt TRAF6 binding
Full-length Act1 constructs carrying R74W showed TRAF6 binding comparable to wild-type in mammalian two-hybrid assays — in sharp contrast to the D10N variant (rs33980500) which loses ~90% of TRAF6-binding capacity. The variant is therefore not itself the mechanistic driver of disease: its disease association derives primarily from strong linkage disequilibrium³³ strong linkage disequilibrium
R²=0.88, D'=0.96 with rs33980500 in European populations, meaning rs13190932-A and rs33980500-T are nearly always inherited together on the same haplotype with the functionally causal D10N variant (rs33980500).

However, the rs13190932 locus carries independent information beyond simple LD tagging. Haplotype analysis in 2,077 PsA cases and 2,648 controls revealed that a four-SNP haplotype including both rs13190932 and rs33980500 carries an odds ratio of 2.7 for psoriatic arthritis⁴⁴ a four-SNP haplotype including both rs13190932 and rs33980500 carries an odds ratio of 2.7 for psoriatic arthritis
This four-SNP haplotype is substantially more predictive than either variant alone, suggesting that regulatory or structural effects from multiple alleles act in concert at this locus. Importantly, rs33980500 (D10N) appears on an additional rarer haplotype background that does not carry rs13190932-A; rs13190932 tracks a subset of the haplotype space that may be particularly enriched for joint (arthritis) versus skin-only (psoriasis vulgaris) disease manifestation.

The Evidence

The initial discovery cohort was 609 German individuals with psoriatic arthritis and 990 controls⁵⁵ 609 German individuals with psoriatic arthritis and 990 controls
Discovery was followed by replication across 6 additional European cohorts totaling 5,488 individuals; combined analysis: OR=1.83 (95% CI 1.59–2.12), P=8.56×10⁻¹⁷. The PsA association (P=8.56×10⁻¹⁷) is approximately 10,000-fold more significant than the psoriasis vulgaris association at the same SNP (P=1.95×10⁻³), suggesting that while rs13190932 tags a shared TRAF3IP2 risk haplotype, the haplotype it tracks is particularly enriched for patients who develop joint involvement.

The variant is essentially monomorphic in East Asian populations⁶⁶ essentially monomorphic in East Asian populations
Both rs13190932 and rs33980500 showed no polymorphism in Han Chinese cohorts studied for Behçet's disease and Vogt-Koyanagi-Harada syndrome — consistent with near-zero allele frequency in East Asian populations in gnomAD. This mirrors the marked ancestral stratification seen in psoriatic arthritis genetics more broadly, where European-derived loci often show minimal variation in East Asian populations that have a distinct psoriasis genetic architecture.

Beyond psoriatic arthritis and psoriasis, rs13190932 has been evaluated across the spectrum of IL-17-pathway autoimmune disease. In systemic lupus erythematosus, all three TRAF3IP2 coding variants (rs33980500, rs13190932, rs13193677) associate with pericarditis development⁷⁷ associate with pericarditis development
Italian cohort of SLE patients: all three TRAF3IP2 SNPs associated with pericarditis; rs13190932-A specifically associated with malar rash (OR=2.14, P=0.041), suggesting the haplotype marked by rs13190932 influences IL-17-mediated vascular and mucocutaneous inflammation across autoimmune contexts.

Practical Implications

Because R74W is not itself the mechanistic driver of disease — its signal derives from LD with D10N — the clinical and practical implications of rs13190932 are best understood as a read-out of the broader TRAF3IP2 risk haplotype. Individuals carrying the A risk allele have substantially elevated psoriatic arthritis risk and warrant the same monitoring and management considerations as D10N (rs33980500) carriers.

The primary practical value of genotyping rs13190932 is as an LD sentinel⁸⁸ LD sentinel
Sentinel variants mark disease association peaks in GWAS; they provide risk stratification even when they are not themselves the causal variants, because they reliably travel with the causal variant in the population for the full TRAF3IP2 risk haplotype. If a genome report includes rs13190932 but not rs33980500, the A allele at rs13190932 provides robust risk stratification for psoriatic arthritis at this locus.

For biologic therapy decisions, the same considerations as D10N apply: the TRAF3IP2 risk haplotype marked by rs13190932 signals impaired canonical IL-17→TRAF6→NF-κB signaling. Anti-IL-17 agents (secukinumab, ixekizumab, brodalumab) and anti-IL-23 agents (guselkumab, risankizumab) each target distinct points in the upstream pathway and may merit consideration relative to anti-TNF agents depending on joint versus skin disease predominance.

Interactions

rs13190932 and rs33980500 (D10N) are in very high LD (R²=0.88) and almost always travel together on the same haplotype. The four-SNP haplotype that includes both variants, plus rs13210247 and rs13196377, carries an OR of 2.7 for psoriatic arthritis — substantially higher than either coding variant alone, indicating additive haplotype effects likely from regulatory variants in non-coding intervals.

The rs13190932 risk haplotype operates within the broader IL-17/Th17 axis. HLA-C rs12191877⁹⁹ HLA-C rs12191877
tags HLA-Cw*0602, the dominant psoriasis susceptibility allele; confers ~30-fold increased risk for type I psoriasis via impaired self-tolerance at the T-cell level creates a dual-hit with the TRAF3IP2 locus: impaired immunological tolerance upstream (HLA) combined with altered IL-17 adaptor signaling downstream (TRAF3IP2). Carriers of both loci likely face synergistic psoriasis and psoriatic arthritis risk that warrants early specialist engagement.