rs3213094 — IL12B Promoter-region

Intronic IL12B variant in linkage with the promoter-regulatory haplotype; T allele is protective against psoriasis and associated with better ustekinumab (anti-p40) response

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IL12B Intronic Variant — Psoriasis Susceptibility and Ustekinumab Response Prediction

The IL12B gene11 IL12B gene
located at 5q33.3, encodes the 40 kDa p40 subunit shared by two functionally distinct cytokines: IL-12 (p40/p35 heterodimer) and IL-23 (p40/p19 heterodimer). IL-12 drives Th1 differentiation and IFN-γ production; IL-23 expands Th17 cells and IL-17 production. Both pathways converge on psoriatic skin inflammation and inflammatory bowel disease. rs3213094 is an intronic variant at chr5:159323761 (GRCh38) within the IL12B gene, lying in strong linkage disequilibrium with the established IL12B regulatory haplotype. While earlier literature referred to this region loosely as "promoter-associated," dbSNP classifies rs3213094 as an intron variant (NM_002187.3:c.89-432G>T). Its significance lies not in direct protein change but in its tight linkage with regulatory elements that govern IL12B expression — and, crucially, in its independent value as a pharmacogenomic predictor of ustekinumab response22 pharmacogenomic predictor of ustekinumab response
Ustekinumab (Stelara) is a monoclonal antibody targeting the p40 subunit encoded by IL12B, blocking both IL-12 and IL-23 simultaneously.

The Mechanism

The T allele at rs3213094 tags a regulatory state of the IL12B locus associated with lower p40 expression. Genome-wide association studies in Chinese Han populations found the T allele to be protective against psoriasis (OR 0.78, combined p = 2.58×10⁻²⁶)33 protective against psoriasis (OR 0.78, combined p = 2.58×10⁻²⁶)
Zhang et al., Nature Genetics 2009, first large Chinese psoriasis GWAS confirming IL12B as a major susceptibility locus, meaning the C allele is the risk-conferring allele. The protective T allele is associated with reduced IL12B transcriptional output in the regulatory environment defined by this haplotype block. This is pharmacogenomically consequential: individuals with one or two copies of the T allele have reduced baseline p40 availability, which changes the pharmacodynamic landscape for drugs targeting p40. For ustekinumab, the CT heterozygous genotype was associated with significantly better PASI reduction at 3 months compared to CC homozygotes in the Galluzzo 2016 study, suggesting that partial reduction of the IL12B risk-haplotype burden may allow ustekinumab to achieve more complete IL-12/23 pathway blockade.

The Evidence

The primary pharmacogenomic study is Galluzzo et al., Dermatology 201644 Galluzzo et al., Dermatology 2016
IL12B (p40) gene polymorphisms contribute to ustekinumab response prediction in psoriasis, a retrospective Italian cohort of 64 patients treated with ustekinumab for up to one year. This study genotyped rs3213094 alongside rs2546890 and found that patients with the CT genotype at rs3213094 had significantly greater mean PASI reduction at 3 months compared to CC homozygotes (p = 0.017). The T allele was the favourable allele. The study also examined interactions with HLA-Cw6, the strongest single predictor of ustekinumab response, and found that IL12B genotype provided additional stratification beyond HLA-Cw6 status.

For psoriasis susceptibility, rs3213094 was confirmed in a two-stage Chinese Han GWAS55 two-stage Chinese Han GWAS
Zhang et al. 2009, 1,139 cases + 1,132 controls discovery; 5,182 cases + 6,516 controls + 539 Uygur cases replication with a combined p-value of 2.58×10⁻²⁶ and an OR of 0.78 for the T allele — placing it among the most statistically robust SNPs at the IL12B locus. European studies of the IL12B haplotype report a complementary picture: the C allele (risk allele) confers elevated psoriasis odds across European populations, with estimates ranging from OR 1.4 to OR 1.9 depending on cohort and analysis model. A meta-analysis of 11 studies confirmed the IL12B risk haplotype in both psoriasis and psoriatic arthritis.

For inflammatory bowel disease, Brinar et al. 201366 Brinar et al. 2013
Multidimensional prognostic risk assessment identifies association between IL12B variation and surgery in Crohn's disease found that IL12B variation was independently associated with need for early surgery within 5 years of Crohn's disease diagnosis, highlighting the shared pathogenic role of the IL12B locus across skin and gut inflammation. A meta-analysis of IL12B polymorphisms in IBD in Caucasian populations confirmed the association of the IL12B susceptibility haplotype with CD and UC risk.

Practical Actions

For individuals carrying the C allele (the risk genotype), two clinical contexts are most relevant. First, psoriasis susceptibility: the CC genotype marks elevated genetic risk for psoriasis and psoriatic arthritis through the same IL-12/23 axis that drives the condition. Second, and more immediately actionable, is biologic therapy planning: if ustekinumab is being considered for psoriasis or Crohn's disease, rs3213094 genotype provides independent pharmacogenomic information. The CT heterozygous genotype is associated with better early PASI response to ustekinumab; CC homozygotes appear to have attenuated benefit at 3 months, though response improves over longer treatment durations in many patients.

For individuals with one or two T alleles who develop psoriasis requiring biologics, this result supports ustekinumab as a rational first-line biologic choice — particularly in combination with HLA-Cw6 positivity, which additively improves response prediction. Guselkumab and risankizumab target only the p19 (IL-23-specific) subunit rather than the shared p40 encoded by IL12B, so their pharmacodynamic relationship with rs3213094 genotype differs from ustekinumab's.

Gut inflammation implications apply across genotypes: the IL12B locus's shared susceptibility with Crohn's disease and ulcerative colitis means carriers of the CC risk genotype with unexplained gastrointestinal symptoms warrant evaluation for subclinical IBD, mirroring the psoriasis-IBD comorbidity recognized in clinical practice.

Interactions

rs3213094 is in linkage disequilibrium with rs3212227 (3'-UTR IL12B) and rs6887695 (upstream IL12B), which together define the canonical IL12B psoriasis risk haplotype. Signals at rs3213094 and rs3212227 are not fully independent — they tag overlapping haplotype blocks — but rs3213094 has been studied as an independent pharmacogenomic marker for ustekinumab response (Galluzzo 2016), complementing the risk-susceptibility role of the haplotype SNPs. rs12188300 (also IL12B, near-gene regulatory) and rs3213094 together provide broader coverage of the IL12B susceptibility locus. rs11209026 (IL23R R381Q) is a protective loss-of-function receptor variant for IL-23; carrying both the IL12B CC risk genotype and IL23R protective A allele (rs11209026) creates a partially antagonistic combination where elevated p40 supply is partially offset by reduced receptor signaling downstream.

Drug Interactions

ustekinumab dose_adjustment literature

Genotype Interpretations

What each possible genotype means for this variant.

CT Protective T Allele Carrier Normal

One copy of the protective IL12B T allele — standard psoriasis risk, better ustekinumab early response

You carry one C and one T allele at rs3213094 in the IL12B gene. This heterozygous genotype is present in approximately 36% of Europeans and is associated with a moderately reduced IL12B-driven psoriasis susceptibility compared to CC homozygotes. Importantly, in the Galluzzo et al. 2016 pharmacogenomic study of ustekinumab in psoriasis, patients with the CT genotype showed significantly better PASI improvement at 3 months compared to CC homozygotes (p = 0.017). The T allele tags a lower-IL12B-expression regulatory state, which appears to allow ustekinumab's anti-p40 blockade to achieve more complete pathway suppression.

TT Homozygous Protective Genotype Normal

Two copies of the protective IL12B T allele — lowest psoriasis risk at this locus

You carry two copies of the T allele at rs3213094, the rarest genotype at this locus (approximately 5% of Europeans, but more common in East Asian populations at roughly 25%). The T allele is associated with reduced IL12B expression in the regulatory haplotype block and confers protection against psoriasis susceptibility — in the large Chinese Han GWAS, the T allele showed OR 0.78 for psoriasis, meaning TT homozygotes have the greatest genetic protection at this locus. For biologic therapy: both the CT and TT genotypes carry the T allele, and TT individuals may have even lower baseline p40 expression than CT, potentially further supporting the mechanistic basis for good ustekinumab response.

CC IL12B Risk Genotype Intermediate

Homozygous for the IL12B risk allele — modestly elevated psoriasis susceptibility, attenuated ustekinumab early response

The CC genotype at rs3213094 reflects the absence of the protective T allele that tags lower IL12B regulatory activity. Individuals with CC have the highest baseline genetic drive toward elevated p40 (IL-12B) expression at this locus, sustaining stronger IL-12 and IL-23 signaling in the Th1 and Th17 inflammatory pathways. In practical terms, this elevates psoriasis susceptibility and, if psoriasis develops, may influence which biologic achieves the best early response.

For biologic therapy: ustekinumab blocks the p40 subunit encoded by IL12B. The pharmacogenomic finding that CC homozygotes respond less robustly at 3 months than CT carriers does not mean ustekinumab is contraindicated — many CC carriers achieve excellent long-term responses — but this genotype result provides useful context for shared decision-making with a dermatologist or gastroenterologist. Longer treatment duration or dose escalation may be warranted for CC homozygotes who show slow initial response.

The IL12B locus is also shared with Crohn's disease and ulcerative colitis susceptibility, making gut symptom awareness relevant regardless of skin manifestations.