rs17266594 — BANK1 Branch-point splice

BANK1 Branch-Point Splice Variant — When One Intron Controls Two Inflammatory Pathways

BANK1 (B-cell scaffold protein with ankyrin repeats 1) is expressed almost exclusively in B cells, where it orchestrates two interconnected arms of immune signaling: B-cell receptor (BCR) activation¹¹ B-cell receptor (BCR) activation
BANK1 scaffolds LYN kinase, IP3 receptors, and PLCγ2 into a complex that mobilizes calcium from the endoplasmic reticulum upon antigen engagement and toll-like receptor (TLR) signaling²² toll-like receptor (TLR) signaling
BANK1 full-length isoform contains a TIR domain in exon 2 that directly binds the TLR adaptor MyD88, linking BANK1 to innate immune pattern-recognition signaling in B cells. The rs17266594 variant sits in intron 1 of BANK1 at the branch-point sequence — a short RNA motif that the spliceosome uses to determine whether exon 2 is included in the mature mRNA. This single intronic change controls which of two BANK1 proteins a B cell predominantly produces, with downstream consequences for both BCR and TLR arms of B-cell activation.

The Mechanism

Alternative splicing of BANK1 produces two isoforms: the full-length (FL) protein that retains exon 2, and the Delta2 (Δ2) isoform that skips exon 2 entirely. Exon 2 encodes a Toll/IL-1 receptor (TIR) domain³³ Toll/IL-1 receptor (TIR) domain
The TIR domain is a conserved protein interaction module found in toll-like receptors and their adaptors; it mediates signal propagation through homotypic TIR-TIR interactions — the same class of domain that enables MyD88 to propagate signals from TLR7 and TLR9 after recognition of viral RNA and DNA.

The rs17266594 variant alters the branch-point consensus sequence immediately upstream of exon 2. The T allele (risk) shifts the isoform balance toward full-length BANK1⁴⁴ T allele (risk) shifts the isoform balance toward full-length BANK1
T allele correlates with higher FL:Δ2 ratio; C allele correlates with higher Δ2 expression in homozygous protective carriers, meaning T carriers produce proportionally more TIR-domain-containing BANK1. The C allele (protective) promotes exon 2 skipping, favoring the Δ2 isoform that lacks the TIR domain.

The functional consequence is mechanistically clear: BANK1-Δ2, lacking the TIR domain, shows significantly reduced binding to MyD88⁵⁵ BANK1-Δ2, lacking the TIR domain, shows significantly reduced binding to MyD88
Co-immunoprecipitation experiments demonstrated markedly decreased BANK1-Δ2 interaction with MyD88 compared to BANK1-FL, confirming the TIR domain is essential for this interaction compared to full-length BANK1. This matters because TLR7 and TLR9 in B cells drive interferon-alpha production and autoantibody generation — the molecular signature of active SLE. When BANK1-FL dominates (T allele), B cells have a stronger TLR-MyD88 signaling axis, amplifying innate immune responses that can break self-tolerance. When BANK1-Δ2 dominates (C allele), this TLR arm is dampened.

rs17266594 is in strong linkage disequilibrium with rs10516487 (R61H) — r²=0.9 in Europeans and r²=1 in Chinese populations — meaning they are nearly always coinherited. The SLE risk haplotype is TGG across rs17266594-rs10516487-rs3733197, while the protective haplotype is CAA. Despite near-complete LD, the two SNPs affect distinct molecular processes: rs10516487 modifies scaffolding complex multimerization and SRp40 splicing enhancer activity, while rs17266594 affects branch-point recognition. Together they constitute a coordinated isoform-control mechanism.

The Evidence

The variant was co-discovered with rs10516487 and rs3733197 in the original BANK1 genome-wide association study⁶⁶ original BANK1 genome-wide association study
Kozyrev et al. used 85,042 SNPs across European SLE cases and controls, identifying rs17266594 as a branch-point splice variant with differential isoform expression dependent on this SNP. In a dedicated European-ancestry replication study of 1,892 SLE cases and 2,652 controls, rs17266594 showed the strongest association signal⁷⁷ rs17266594 showed the strongest association signal
Despite being intronic, rs17266594 produced the strongest BANK1-SLE signal in this cohort: corrected P=1.97×10⁻⁵, OR=1.22 (95% CI 1.12–1.34) among all BANK1 variants tested — a notable finding for a non-coding SNP.

Replication across ancestries is robust. In Hong Kong Chinese⁸⁸ Hong Kong Chinese
949 SLE cases, 1,042 controls; the protective C allele OR=0.61 (95% CI 0.51–0.72), P=4.67×10⁻⁹, with r²=1 LD with rs10516487 in HapMap HCB Chinese, the association was stronger than in Europeans. In Chinese Han patients, the T allele was enriched among SLE patients and was significantly associated with high-titre ANA and anti-SSA antibodies⁹⁹ significantly associated with high-titre ANA and anti-SSA antibodies
Among BANK1 variant carriers with SLE, rs17266594 T allele showed specific enrichment for ANA ≥1:320 and Ro/SSA autoantibodies — autoantibody specificities that mark active, organ-threatening disease.

A meta-analysis of 22 studies¹⁰¹⁰ meta-analysis of 22 studies
Bae and Lee 2017; 22,684 patients and 36,437 controls across SLE, RA, and SSc; BANK1 rs17266594 T allele pooled OR=1.19 (95% CI 1.07–1.32), P=0.001 across all autoimmune diseases confirmed the disease-specific pattern: significant association for SLE (OR=1.41) and systemic sclerosis (OR=1.09), but no significant RA association — distinguishing rs17266594 from rs3733197 (A383T), which does associate with RA when the BLK risk background is also present.

B-cell functional studies showed that individuals carrying the BANK1 risk haplotype (TGG) have altered proximal BCR signaling¹¹¹¹ altered proximal BCR signaling
Risk haplotype carriers show reduced phospho-PLCγ2 and phospho-AKT, increased FOXO1 expression, and expanded memory B-cell compartment — a pro-autoimmune B-cell developmental bias, with expanded memory B cells and blunted immediate BCR activation markers, consistent with a B-cell population primed for autoantibody differentiation over acute antigen response.

Practical Actions

Carrying the TT genotype means your BANK1 produces predominantly the full-length isoform with intact TIR domain, giving your B cells enhanced responsiveness to both BCR stimulation and TLR7/TLR9 ligands such as viral RNA and DNA. This does not cause autoimmune disease independently — environmental triggers (UV light, viral infections, estrogen cycling), HLA haplotype, and other BANK1 and BLK variants are all required co-factors. Most T allele carriers will never develop SLE or SSc. However, the variant meaningfully shifts probability, and early recognition of symptoms — malar rash, persistent joint pain, Raynaud's phenomenon, persistent dry mouth or eyes, photosensitivity — warrants prompt rheumatologic evaluation rather than watchful waiting.

Because rs17266594 and rs10516487 are in near-complete LD, their clinical implications substantially overlap: both tag the same risk haplotype in most individuals. Where they differ is in Chinese populations (r²=1) where rs17266594 is the sole independent tag needed, and in the specific mechanism it illuminates — the TLR-MyD88 axis — which has direct therapeutic relevance. Belimumab (anti-BAFF) and hydroxychloroquine remain the best-evidenced interventions for SLE once diagnosed, regardless of BANK1 genotype. However, the TLR-MyD88 connection suggests that TLR7/TLR9 antagonists (under clinical development for SLE) may be particularly relevant for T allele carriers.

Interactions

rs17266594 is nearly always coinherited with rs10516487 (R61H) as part of the BANK1 risk haplotype TGG (rs17266594-rs10516487-rs3733197). The two SNPs affect distinct molecular mechanisms — branch-point splicing versus SRp40 splicing enhancer and protein multimerization — but their effects converge on the same phenotype (increased full-length:Δ2 isoform ratio and amplified B-cell activation). When interpreting these two SNPs, genotype concordance is expected in most people; a rare discordant individual (TC at rs17266594, GG at rs10516487) may have partially additive effects.

The BLK rs13277113 variant (reduced BLK expression in B cells) shows documented gene-gene interaction with BANK1 variants¹²¹² documented gene-gene interaction with BANK1 variants
BLK and BANK1 gene-gene interaction confirmed by logistic regression (P=0.013), MDR (P<0.0001), and linear regression (P=0.0017) in SLE susceptibility — when risk alleles at both loci are present, the combined SLE risk substantially exceeds individual contributions. Similarly, STAT4 rs7574865 (amplified JAK-STAT interferon signaling) compounds with BANK1 variants because the TLR-MyD88-IFN-α axis activated by full-length BANK1 feeds directly into the STAT4 pathway. Individuals carrying risk alleles at rs17266594 (or rs10516487), rs13277113, and rs7574865 simultaneously represent the highest-risk genetic tier for SLE among the SNPs in this database.