rs2469434 — CD226

CD226 Intronic Variant — A Regulatory Signal at the DNAM-1 Autoimmune Locus

CD226 (also known as DNAM-1, DNAX Accessory Molecule-1)¹¹ CD226 (also known as DNAM-1, DNAX Accessory Molecule-1)
A co-stimulatory receptor expressed on T cells, natural killer cells, and myeloid cells that delivers activating signals when it binds PVR (CD155) or Nectin-2 (CD112) on antigen-presenting cells and stressed tissues is one of the few genes in the human genome where both coding and non-coding genetic variation independently contribute to autoimmune risk. rs2469434 sits deep within an intron of CD226 on chromosome 18q22, roughly 12,000 base pairs from the functionally well-characterised coding variant rs763361 (Gly307Ser). The two variants capture distinct signals at the same locus: rs763361 changes the protein's cytoplasmic signalling domain, while rs2469434 is thought to act through regulatory mechanisms — altering CD226 expression levels in immune cells rather than protein structure.

The Mechanism

rs2469434 maps to the notation c.728-3564 in the canonical CD226 transcript (NM_006566.4), placing it 3,564 nucleotides upstream of a major exon boundary — far from splice sites and beyond the reach of conventional splicing effects. The most plausible functional interpretation is that this variant lies within an intronic enhancer or silencer element²² enhancer or silencer element
Regulatory DNA sequences within introns that bind transcription factors and modulate gene expression levels without altering the protein sequence, modulating CD226 transcription in immune cell types. The GWAS signal for altered neutrophil count and total white blood cell count — two haematopoietic phenotypes with high expression in circulating immune cells — is consistent with a cis-regulatory effect on CD226 expression during immune cell maturation and differentiation.

CD226 itself delivers co-stimulatory signals that lower the activation threshold of both innate NK cells and adaptive T cells. Higher expression of the receptor (or dysregulated expression timing) translates into lower thresholds for immune cell activation — the cellular substrate for autoimmune tissue damage. The C risk allele at rs2469434 is associated with increased neutrophil count and elevated WBC in the largest multi-ethnic blood cell GWAS to date (Chen MH et al. 2020, 746,667 individuals)³³ (Chen MH et al. 2020, 746,667 individuals), consistent with a CD226 regulatory effect on myeloid cell development or survival.

The Evidence

The rheumatoid arthritis association at rs2469434 was established by the landmark Okada et al. 2014 RA GWAS meta-analysis⁴⁴ Okada et al. 2014 RA GWAS meta-analysis
Okada Y et al. Genetics of rheumatoid arthritis contributes to biology and drug discovery. Nature, 2014; >100,000 subjects, 29,880 RA cases, 73,758 controls, which mapped 42 novel RA risk loci including the CD226 18q22 region. The C allele shows an odds ratio of approximately 1.07 (95% CI 1.05–1.10) in European populations and 1.11 (95% CI 1.07–1.15) in East Asian populations, with genome-wide significance (P=9×10⁻¹⁰ and 1×10⁻⁸ respectively). These effect sizes are modest — consistent with the polygenic architecture of RA, where each individual variant contributes a small increment to cumulative risk.

The multiple sclerosis association comes from the International MS Genetics Consortium 2019 study⁵⁵ International MS Genetics Consortium 2019 study
Published in Science, 47,429 MS cases and 68,374 controls; established 200 autosomal susceptibility variants outside the MHC, which found rs2469434-C associated with MS susceptibility at OR 1.055 (P=3×10⁻⁸).

Importantly, the haematopoietic phenotype associations — neutrophil count (P=10⁻¹⁶) and total WBC count (P=5×10⁻¹³) from Chen MH et al. 2020 — provide mechanistic support for the autoimmune risk associations. Both phenotypes are cellular traits with well-known links to immune activation and autoimmune disease activity: elevated neutrophil counts are observed in active RA and MS flares, and circulating neutrophil levels are an intermediate phenotype between CD226 regulatory variants and clinical autoimmune disease expression.

Practical Implications

The per-allele ORs from this intronic variant (1.07–1.11 for RA, 1.055 for MS) are modest but real, and they act independently of the better-characterised rs763361 (Gly307Ser) coding variant. For CC homozygotes carrying two C alleles, the cumulative effect is approximately the square of the per-allele OR — roughly 1.14–1.23 × the risk of TT homozygotes, depending on the disease. In the context of RA and MS, which are both T-cell-mediated diseases with well-defined early biomarkers, monitoring for early signs is the primary actionable response.

Interactions

rs2469434 and rs763361 both map to the CD226 locus and independently associate with overlapping autoimmune diseases. Their independence as signals means a person can carry risk alleles at both variants, producing a compound effect at the CD226 locus beyond what either variant predicts alone. More broadly, the CD226 18q22 locus interacts pathogenically with other T-cell checkpoint genes: PTPN22 rs2476601 (LYP phosphatase), CTLA4 rs3087243 and rs231775 (inhibitory co-receptor), and IL2RA rs2104286 (IL-2 receptor alpha). All four genes converge on the T-cell activation/tolerance decision, and elevated CD226 expression from rs2469434 would amplify the effect of any co-existing checkpoint gene risk alleles.