rs2004640 — IRF5 G198T

IRF5 G198T — Autoimmune Disease Risk Through Altered Interferon Signaling

The rs2004640 variant in the IRF5 (interferon regulatory factor 5) gene is one of the most well-established genetic risk factors for autoimmune diseases. This single nucleotide change in the first intron of IRF5 creates an alternative splice donor site¹¹ creates an alternative splice donor site
The T allele generates a new 5' donor splice site in exon 1B, allowing transcription of unique IRF5 isoforms, fundamentally altering how the immune system responds to threats. IRF5 is a transcription factor that acts as a master regulator of type I interferon production²² type I interferon production
Type I interferons (IFN-α and IFN-β) are cytokines critical for antiviral immunity but also drive autoimmune inflammation when dysregulated and proinflammatory cytokines including TNF-α, IL-6, and IL-12. When this splice site variant is present, it leads to expression of IRF5 isoforms with enhanced activity, tipping the balance toward chronic immune activation.

The Mechanism

The rs2004640 variant is a G-to-T substitution located 198 base pairs downstream of exon 1A in the first intron of IRF5. The T allele creates a functional 5' splice donor site that enables use of an alternative first exon (exon 1B), resulting in alternative splicing patterns and increased IRF5 expression³³ alternative splicing patterns and increased IRF5 expression
Multiple IRF5 splice variants exist with the T allele producing isoforms that have increased stability and transcriptional activity. IRF5 functions downstream of toll-like receptors (TLRs)⁴⁴ toll-like receptors (TLRs)
Pattern recognition receptors that detect viral and bacterial molecular signatures in the MyD88-dependent pathway. Upon activation by viral or self-nucleic acids, IRF5 translocates to the nucleus and binds to interferon-stimulated response elements (ISREs) in the promoters of type I interferon genes and inflammatory cytokine genes. The alternative isoforms produced by the T allele appear to have greater transcriptional activity and longer half-lives, leading to sustained interferon production even in the absence of ongoing infection.

The Evidence

The association between rs2004640 and autoimmune disease has been replicated across multiple ethnicities and conditions. For systemic lupus erythematosus (SLE)⁵⁵ systemic lupus erythematosus (SLE)
A chronic autoimmune disease characterized by immune complex deposition, autoantibody production, and multi-organ inflammation, a comprehensive meta-analysis of 28 studies including 11,228 SLE cases and 14,374 controls found that individuals carrying the T allele had a 39% increased risk (OR=1.393, 95% CI: 1.276-1.522). The association held across Asians (OR=1.256), Europeans (OR=1.338), and Latin Americans (OR=1.853). A Korean replication study⁶⁶ Korean replication study
Study of 593 SLE patients and 972 controls demonstrated an odds ratio of 1.44 for the T allele, with the strongest signal coming from the rs2004640-T/rs2280714-T haplotype.

Beyond lupus, rs2004640 confers risk for systemic sclerosis (scleroderma)⁷⁷ systemic sclerosis (scleroderma)
Autoimmune disease characterized by fibrosis of skin and internal organs. In a French cohort of 881 systemic sclerosis patients, the TT genotype was associated with a 58% increased risk (OR=1.58, p=0.002) and showed particularly strong association with pulmonary fibrosis (OR=2.07). Multivariate analysis confirmed that the IRF5 variant remained independently associated with lung involvement even after accounting for disease subtype and autoantibody status. The variant is also associated with Sjögren syndrome⁸⁸ Sjögren syndrome
Autoimmune disease primarily affecting salivary and lacrimal glands, causing dry mouth and eyes, where 87% of patients carried the GT or TT genotype compared to 77% of controls (OR=1.93).

For rheumatoid arthritis, the evidence is more mixed. A meta-analysis of 4,818 RA cases⁹⁹ meta-analysis of 4,818 RA cases
Analysis pooling data from six case-control studies across eight countries found that the T allele was associated with a modest 14% increased risk when using a dominant genetic model (TT + TG versus GG: OR=1.14, p=0.003). The association was stronger in Caucasians (OR=1.25 for TT versus GG) than in Asian populations. Interestingly, one French study found no association with RA and even a slight undertransmission of the T allele from parents to affected offspring, suggesting the IRF5 risk architecture may differ between SLE and RA.

Practical Implications

If you carry one or two copies of the T allele, you have a moderately elevated genetic risk for developing autoimmune conditions, particularly lupus, systemic sclerosis, and Sjögren syndrome. This does not mean you will develop these diseases — most people with the T allele remain healthy — but it does mean your immune system may be primed toward higher interferon production and inflammatory responses. Early recognition of autoimmune symptoms becomes more important.

There are no specific medications or supplements that directly counteract the IRF5 variant's effects. However, understanding your genetic predisposition can inform monitoring strategies. If you develop early signs of autoimmune disease (persistent joint pain, unexplained rashes, chronic dry eyes and mouth, Raynaud phenomenon, or unexplained fatigue), seek medical evaluation promptly. Early diagnosis and treatment of autoimmune conditions significantly improves long-term outcomes. Some evidence suggests that vitamin D deficiency may amplify autoimmune risk¹⁰¹⁰ vitamin D deficiency may amplify autoimmune risk
Vitamin D has immunomodulatory effects and deficiency is common in autoimmune diseases, so maintaining adequate vitamin D status through sun exposure or supplementation may be prudent.

Interactions

The rs2004640 variant often occurs on haplotypes with other functional IRF5 polymorphisms. The most well-studied is the combined rs2004640-T/rs2280714-T haplotype, which has been associated with even stronger risk than either variant alone (pooled p=2.11×10⁻¹⁶ for SLE). The rs2280714 variant affects the polyadenylation signal, producing a shorter and more stable IRF5 mRNA, while rs2004640 affects splicing. Together, they create a "double hit" leading to both altered isoform production and increased transcript stability. A 5-bp insertion/deletion polymorphism (CGGGG indel) in the IRF5 promoter is also in strong linkage disequilibrium with rs2004640 and increases binding of the SP1 transcription factor, further amplifying IRF5 expression.

IRF5 also shows gene-gene interactions with STAT4, another key regulator of interferon signaling. Individuals carrying risk alleles at both IRF5 (rs2004640) and STAT4 (rs7574865) have additive risk for systemic sclerosis and interstitial lung disease that exceeds the risk from either variant alone. This likely reflects convergent effects on the type I interferon pathway, with STAT4 acting downstream of interferon receptor signaling while IRF5 controls interferon production. The combined effect suggests that individuals with both variants have sustained activation of the interferon system from both increased cytokine production and enhanced cellular responses to those cytokines.

For individuals of mixed ancestry, it's worth noting that the T allele frequency varies substantially: approximately 52% in Europeans, 34% in East Asians, 47% in Africans, and 38% in South Asians. This population structure means that risk perception should be calibrated to ancestry-specific frequencies. However, the functional effect of the T allele appears consistent across populations — when present, it increases autoimmune risk regardless of ethnic background.