rs13193677 — TRAF3IP2

TRAF3IP2 rs13193677 — An IL-17 Pathway Locus Variant Linking Systemic Lupus Erythematosus to Pericarditis Risk

TRAF3IP2 encodes Act1 (also called CIKS — Connector of IKK and Stress-activated kinases), the essential adaptor protein for IL-17 receptor signaling¹¹ the essential adaptor protein for IL-17 receptor signaling
Act1 bridges the cytoplasmic domain of IL-17RA/IL-17RC to TRAF6, activating NF-κB and inflammatory gene expression in keratinocytes, fibroblasts, and mucosal epithelial cells; it is also a negative regulator of B-cell adaptive immunity via its interaction with the CD40 signaling complex. While the most studied variants at this locus — D10N (rs33980500) and R74W (rs13190932) — affect the Act1 protein directly, rs13193677 was identified in the same three-SNP panel as part of a 2013 Italian cohort study that extended TRAF3IP2 disease associations beyond psoriasis and psoriatic arthritis into systemic lupus erythematosus (SLE) territory.

The Variant

rs13193677 sits at chr6:154,297,800 (GRCh38). Current dbSNP annotation places it within the IPCEF1 gene (interaction protein for cytohesin exchange factors 1) at chromosome 6q25.2 — approximately 43 megabases distal to the canonical TRAF3IP2 locus at 6q21. This chromosomal distance means rs13193677 cannot be in significant linkage disequilibrium with the TRAF3IP2 coding variants (rs33980500, rs13190932) by standard LD block structure.

The Ciccacci 2013 investigators selected rs13193677 as part of their TRAF3IP2 panel based on earlier TRAF3IP2 literature and genotyping array content, but the variant's independent association with SLE susceptibility (OR=1.73, P=0.046) and pericarditis in that cohort likely reflects an action at the IPCEF1/6q25.2 locus itself rather than a TRAF3IP2 LD-tagging effect. IPCEF1 encodes a protein that regulates ARF6 GEF activity through cytohesin-2, participates in membrane trafficking, and shows nerve injury-responsive expression — a functional context distinct from Act1/IL-17 signaling.

On the plus strand (as reported by dbSNP), the reference allele is G and the alternate allele is A. The A allele is rare in East Asian populations (~0.1%) but reaches ~9% in Europeans and ~13% in Africans, consistent with the population distribution of many autoimmune risk alleles.

The Evidence

The primary evidence comes from Ciccacci et al. 2013²² Ciccacci et al. 2013
Case-control study of 239 consecutive SLE patients meeting ACR criteria and 278 age/ethnicity-matched Italian controls; genotyping by allelic discrimination with TaqMan probes. The three TRAF3IP2-panel SNPs (rs33980500, rs13190932, rs13193677) were genotyped together. rs13193677 showed association with SLE susceptibility at P=0.046, OR=1.73, reaching nominal significance. The effect was comparable to rs33980500 (P=0.021, OR=1.71) but with borderline statistical confidence — consistent with a modest additive risk contribution rather than a strong causal effect.

All three SNPs were associated with pericarditis development as a disease complication, with rs33980500 showing the strongest pericarditis association (P=0.002, OR=2.59). The combined pericarditis signal across the panel suggests either shared haplotype effects, shared immune pathways, or that the specific SLE autoimmune cardiac manifestation is particularly sensitive to variation at these loci. Pericarditis occurs in 20–30% of SLE patients over their disease course and is a major driver of morbidity and hospitalisation.

The OR of 1.73 is moderate in magnitude and derives from a single study in an Italian cohort (n=517 total). Independent replication in larger and more diverse SLE cohorts has not been published to date. This limits confidence to the moderate evidence tier: biologically plausible IL-17 pathway connection, nominal statistical significance, but not yet replicated at genome-wide significance in SLE-specific GWAS.

Practical Actions

Carriers of the A allele should be aware of its association with SLE susceptibility and particularly with pericarditis as a disease manifestation. Early recognition of pericarditis symptoms in SLE patients — pleuritic chest pain worsened by lying flat, friction rub on auscultation, pericardial effusion on echocardiography — is critical because SLE pericarditis responds to colchicine and NSAIDs when identified early, and tamponade or constrictive pericarditis can complicate untreated or recurrent episodes.

Given the borderline statistical confidence and single-cohort evidence base, this variant is best interpreted as a modifier that, when co-occurring with other SLE susceptibility alleles or in individuals with established SLE, raises awareness for cardiac monitoring.

Interactions

rs13193677 was studied alongside rs33980500 (D10N) and rs13190932 (R74W) as part of the TRAF3IP2 variant panel in the Ciccacci 2013 cohort. All three variants showed association with pericarditis development, suggesting additive or independent contributions across the panel to cardiac autoimmune risk in SLE.

rs33980500 (D10N) and rs13190932 (R74W) are the primary functional and GWAS variants at the TRAF3IP2 locus. D10N disrupts Act1-TRAF6 binding and paradoxically drives Th17 hyperactivation; R74W is the strongest GWAS signal for psoriatic arthritis. These coding variants operate through the IL-17 pathway in skin and joints; their contribution to SLE pericarditis through the same pathway — IL-17 drives pericardial inflammation — provides a mechanistic frame for the Ciccacci 2013 findings.

rs2476601 (PTPN22 R620W) is an established SLE susceptibility variant. Carrying both rs13193677-A and rs2476601-A would represent convergent risk from the IL-17 signaling and T-cell activation checkpoints respectively.