rs2488457 — PTPN22

PTPN22 -1123G>C — A Second Voice in the Same Gene

The PTPN22 gene is best known for its coding variant rs2476601 (R620W), the strongest non-HLA risk factor for autoimmunity in Europeans. But the gene harbors a second clinically relevant variant in its promoter region: -1123G>C (rs2488457), located 1,123 base pairs upstream of the transcription start site. Unlike R620W, which changes the protein's structure, this promoter variant sits in regulatory territory — influencing not what PTPN22 does, but [how much of it is made | Promoter variants affect transcription factor binding and thus the rate of mRNA production from the gene]. Its significance depends heavily on ancestry: in Asian populations, where R620W is virtually absent, -1123G>C stands alone as a primary PTPN22 risk signal¹¹ stands alone as a primary PTPN22 risk signal
In Chinese and Japanese cohorts, rs2476601 is non-polymorphic while rs2488457 shows independent association with RA, T1D, LADA, JIA, and UC. In Europeans, it rides along with the R620W haplotype and cannot be disentangled from it²² cannot be disentangled from it
Norwegian cohort study found -1123G>C association statistically indistinguishable from 1858C>T in RA in most cohorts.

The Mechanism

The -1123G>C change alters a nucleotide in the 5' regulatory region of PTPN22, a zone that binds transcription factors controlling how actively the gene is transcribed. Expression studies have found a tendency for association between -1123G>C and PTPN22 mRNA levels³³ tendency for association between -1123G>C and PTPN22 mRNA levels
Chinese RA study found expression analysis indicated association between -1123G>C and PTPN22 gene expression levels, though the direction and magnitude have not been pinned down with the same precision as functional coding variants. A Chinese ulcerative colitis study found dramatically elevated PTPN22 mRNA in inflamed colonic tissue⁴⁴ dramatically elevated PTPN22 mRNA in inflamed colonic tissue
PTPN22 mRNA significantly higher in inflamed vs non-inflamed colon; correlated with CRP r=0.578, p<0.001, with expression levels correlating with disease severity and systemic inflammation markers. Whether the promoter variant drives this upregulation, or is a passenger tagging another functional element, remains an open question.

A graft-versus-host disease study provided an unexpected functional clue: bone marrow transplant recipients carrying the CC genotype had lower incidence of acute GvHD⁵⁵ CC genotype had lower incidence of acute GvHD
C/C recipients HR 0.50 for grade II-IV acute GvHD compared to G/G carriers, but higher relapse rate HR 1.78 but higher relapse rates — the classic immune-suppression trade-off. This suggests the C allele (the common protective variant) may dampen immune responsiveness, while the G allele sustains a more active immune phenotype that fights both GvHD targets and autoantigens.

The Evidence

The variant's association spectrum spans multiple autoimmune conditions, but with marked population stratification⁶⁶ marked population stratification
Variant is polymorphic and shows independent autoimmune associations in Asian populations; in Europeans, tight LD with R620W makes independent contribution undetectable:

In Asian populations where R620W is absent, -1123G>C shows independent associations. A Japanese/Korean study found OR=1.41-1.42 for acute-onset type 1 diabetes⁷⁷ found OR=1.41-1.42 for acute-onset type 1 diabetes
Promoter SNP associated with acute-onset but not slow-onset T1D; OR=1.42 in Japanese, combined OR=1.41, with the authors arguing the promoter SNP is "a more likely causative variant" than R620W in these populations. A Chinese RA study found OR=1.52 for RA in Han Chinese⁸⁸ OR=1.52 for RA in Han Chinese
494 cases and 496 controls; R620W was non-polymorphic in this cohort. A Chinese LADA study reported OR=1.99 for latent autoimmune diabetes⁹⁹ OR=1.99 for latent autoimmune diabetes
Significant association in Chinese Hans; R620W showed no association in same cohort. In juvenile idiopathic arthritis, a Han Chinese study found OR=2.15 for GC/CC combined vs GG¹⁰¹⁰ OR=2.15 for GC/CC combined vs GG
137 JIA cases vs 150 controls; C allele OR=1.95.

A meta-analysis of uveitis¹¹¹¹ meta-analysis of uveitis
8 studies; OR=1.18 overall, OR=1.21 in Asian populations; weaker signal in Europeans found modest but significant association. For primary immune thrombocytopenia¹²¹² primary immune thrombocytopenia
Meta-analysis of 10 studies, 932 cases; G allele carriers OR=1.23; GG homozygotes 1.51× more susceptible than CC carriers, a meta-analysis found G allele carriers at modestly elevated risk.

In European populations, a Czech/Azeri study concluded no independent contribution¹³¹³ no independent contribution
Only R620W haplotype drove disease risk; -1123G>C alone conferred no additional risk from -1123G>C in T1D or JIA. The Norwegian RA study could not distinguish¹⁴¹⁴ could not distinguish
Tight LD between the two variants makes conditional analysis impossible in European samples between the two variants' contributions. In Europeans, this variant's clinical relevance is primarily as a tag for the R620W haplotype.

Practical Implications

The G allele (minor allele: ~22% in Europeans, ~40% in East Asians) is the risk variant associated with altered PTPN22 expression and modestly elevated autoimmune susceptibility. Risk associations are modest (OR 1.2–2.0 depending on condition and ancestry) and context-dependent. For individuals of East Asian ancestry, this variant has independent predictive value where R620W is not relevant. For individuals of European ancestry, carrying the G allele is primarily informative as a haplotype marker — its combined effect with R620W (rs2476601) on the same haplotype amplifies the overall PTPN22 risk signal, and joint genotyping provides fuller picture than either variant alone.

Monitoring guidance follows the same logic as for other PTPN22 variants: awareness of early autoimmune symptoms (joint inflammation, thyroid changes, skin changes, fatigue) and prompt evaluation if they develop. The variant does not point to a specific actionable intervention but raises the baseline vigilance warranted for immune dysregulation.

Interactions

rs2488457 and rs2476601 (R620W) are the two best-characterized PTPN22 variants, and their relationship depends on ancestry¹⁵¹⁵ their relationship depends on ancestry
In Europeans, both are on the same high-risk haplotype and are in tight LD; in Asian populations, rs2476601 is absent and rs2488457 acts independently. Czech and Azeri haplotype analysis showed only haplotypes carrying the R620W minor allele conferred disease risk — adding -1123G>C to a non-R620W haplotype added nothing. This makes the two variants co-travelers in Europeans but independent signals in Asians.

A third PTPN22 variant, rs33996649 (+788G>A), is also non-polymorphic in most Asian populations and tracks with R620W in Europeans, adding to the picture of a PTPN22 "risk haplotype" in Europeans that encodes multiple regulatory and coding changes simultaneously.

Compound interactions between rs2488457 and HLA loci have not been formally characterized but are expected to follow the same pattern as R620W: convergent independent risk from PTPN22 and HLA without strong epistasis.