rs13196377 — TRAF3IP2 Intronic haplotype member

TRAF3IP2 rs13196377 — The Haplotype Anchor That Completes the IL-17 Adaptor Risk Map

When geneticists mapped the TRAF3IP2 psoriasis susceptibility locus on chromosome 6q21, they found not one disease signal but two overlapping risk haplotypes. The two coding variants — D10N (rs33980500) and R74W (rs13190932) — explain much of the risk, but complete haplotype resolution requires four SNPs¹¹ complete haplotype resolution requires four SNPs
The four-SNP haplotype (rs13196377 + rs13190932 + rs33980500 + rs13210247) was identified by haplotype analysis in psoriatic arthritis GWAS to carry a combined P=1.39×10⁻¹² and OR=2.7 for PsA; the variant set captures two distinct risk haplotypes that would be missed by coding variants alone. rs13196377 is the fourth and final member of that set — an intronic tagging variant whose primary job is to distinguish which risk haplotype background a chromosome sits on.

TRAF3IP2 encodes Act1 (CIKS — Connection to IKK and Stress-activated protein kinase), the essential adaptor protein that couples the IL-17 receptor to NF-κB inflammatory signalling. The gene is located on the minus strand and is flanked on the plus strand by its antisense lncRNA TRAF3IP2-AS1. rs13196377 falls inside an intron of TRAF3IP2 and also overlaps the TRAF3IP2-AS1 transcript body — the same regulatory territory where rs13210247 (the lncRNA gain-of-function variant) operates.

The Mechanism

rs13196377 has no known direct functional consequence: it does not alter a coding sequence, splice site, or transcription factor binding motif in any study to date. Its disease association is mediated entirely through linkage disequilibrium with the causal variants in the locus²² linkage disequilibrium with the causal variants in the locus
Linkage disequilibrium (LD) means alleles at nearby positions are inherited together more often than expected by chance; a tagging SNP like rs13196377 carries risk information purely because it co-segregates with functionally important alleles on the same chromosomal segment.

What makes rs13196377 structurally useful is the two-haplotype architecture of the TRAF3IP2 locus. Haplotype analysis in psoriasis case-control cohorts identified two independent risk haplotypes:

• Primary haplotype (OR=2.7): carries the common G allele at rs13196377 alongside rs33980500-T (the D10N coding variant that nearly abolishes TRAF6 binding) and rs13210247-A. This is the high-risk haplotype, dominated mechanistically by D10N.
• Secondary haplotype (OR=1.8): carries the minor A allele at rs13196377 alongside rs13190932-A (R74W) and rs13210247-G. This haplotype lacks D10N yet still confers elevated disease risk — suggesting additional regulatory or structural contributions from the non-coding variants it carries.

The G allele alone carries no independent risk information: it is simply the common background allele present on the majority of chromosomes, including the primary risk haplotype. The A allele is the informative minor allele, marking the secondary risk haplotype that is missed if only coding variants are genotyped. Without rs13196377 in the panel, approximately one in twelve European chromosomes carrying a TRAF3IP2 risk haplotype would be misclassified as wild-type.

The Evidence

The four-SNP haplotype was first characterised in the discovery cohort of the Hüffmeier et al. 2010 Nature Genetics study³³ Hüffmeier et al. 2010 Nature Genetics study
Combined analysis of 609 German PsA patients and 990 controls, replicated across six European cohorts totalling over 4,700 individuals; the four-SNP haplotype reached combined P=1.39×10⁻¹² for psoriatic arthritis. rs13196377 was included in the haplotype because it captured haplotype-phase information that coding variants alone did not resolve.

In a dedicated haplotype analysis of 1,034 psoriasis cases and controls, Dębniak et al. 2014⁴⁴ Dębniak et al. 2014
Study examined four TRAF3IP2 variants in a Polish psoriasis case-control series; minor alleles of all four variants were more frequent in cases; haplotype analysis revealed two distinct risk backgrounds differentiated by rs13196377 allele status confirmed that the A allele marks a secondary haplotype with independent association (OR=1.8, P=0.0008) distinct from the primary D10N-driven haplotype (OR=2.7).

Beyond psoriasis and psoriatic arthritis, Ciccacci et al. 2013⁵⁵ Ciccacci et al. 2013
Examined 267 Crohn's disease patients, 200 ulcerative colitis patients, and 278 controls; three TRAF3IP2 SNPs were genotyped including rs13196377; association with cutaneous extraintestinal manifestations (pyoderma gangrenosum and erythema nodosum) was the primary outcome found that in ulcerative colitis patients, rs13196377-A conferred an odds ratio of 4.1 (P=0.049) for cutaneous extraintestinal manifestations — pyoderma gangrenosum and erythema nodosum. This signal was independent of the primary IBD susceptibility association and suggests that the secondary haplotype tagged by the A allele has particular relevance to mucocutaneous inflammation in the IBD context.

Practical Implications

For most individuals, rs13196377 in isolation provides limited independent clinical guidance: its value lies in haplotype-resolved risk reporting when combined with the other three TRAF3IP2 markers. Carrying the A allele at rs13196377 without knowing the rs33980500 status means you are on the secondary risk haplotype, which carries a psoriasis OR of approximately 1.8 — real but meaningfully lower than the primary haplotype. The practical implications follow the same disease management principles as for the other TRAF3IP2 locus variants: monitoring for psoriasis and psoriatic arthritis onset, awareness of medication triggers, and biologic therapy selection guidance when treatment is needed.

IBD patients with the A allele warrant heightened awareness of cutaneous extraintestinal manifestations — particularly pyoderma gangrenosum, which is painful, disfiguring, and requires early immunosuppressive intervention when it develops at the perianal or peristomal site.

For genome reports that include all four TRAF3IP2 haplotype variants, rs13196377 allele status directly refines the haplotype call: A allele places the individual on the secondary haplotype; G allele is consistent with either the common neutral background or the primary risk haplotype (distinguished by rs33980500 status).

Interactions

rs13196377 completes the four-SNP TRAF3IP2 haplotype panel alongside rs33980500 (D10N, functionally causal), rs13190932 (R74W, LD sentinel for primary haplotype), and rs13210247 (lncRNA gain-of-function, regulatory component). When all four are available, haplotype-phase can be resolved to distinguish the OR=2.7 and OR=1.8 risk haplotypes, providing the most accurate TRAF3IP2 risk stratification currently achievable from population-level data.

The TRAF3IP2 risk locus operates downstream of HLA-C rs12191877⁶⁶ HLA-C rs12191877
Tags HLA-Cw*0602, the dominant psoriasis susceptibility allele conferring ~30-fold elevated risk for type I psoriasis via impaired T-cell tolerance; confers highest risk in early-onset plaque psoriasis; modifies ustekinumab response in the IL-17 pathway hierarchy. Carriers of both the TRAF3IP2 A-allele haplotype and HLA-Cw*0602 face convergent risk from impaired immune tolerance upstream and altered IL-17 adaptor signalling downstream.