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 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 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 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 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 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 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 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 Chinese | 494 cases and 496 controls; R620W was non-polymorphic in this
cohort. A Chinese LADA study
reported 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 GG | 137
JIA cases vs 150 controls; C allele OR=1.95.
A 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 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
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 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 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.
Alla genotyper
Two copies of the common allele — standard PTPN22 expression profile
You carry two copies of the common C allele, which is found in approximately 60% of Europeans and 80% of people globally. This represents the population- major genotype. PTPN22 expression is at its typical level for this allele combination. Your autoimmune risk from this specific variant is at baseline — other factors, including the nearby PTPN22 R620W variant (rs2476601), are more influential determinants of PTPN22-related immune regulation.
One copy of the minor G allele — modestly altered PTPN22 regulation
You carry one copy of the minor G allele at the PTPN22 promoter, a combination found in approximately 35% of Europeans. Evidence from multiple Asian populations shows G allele carriers have modestly elevated autoimmune susceptibility (OR approximately 1.2–1.9 depending on condition and population), though in European cohorts this signal is inseparable from the linked R620W coding variant. The heterozygous state is associated with intermediate effects on PTPN22 expression. For people of East Asian ancestry, this variant has independent predictive significance where R620W is absent.
Two copies of the minor G allele — most altered PTPN22 promoter activity
You carry two copies of the minor G allele, a genotype found in approximately 5% of Europeans and about 16% of East Asians. This is the genotype most consistently associated with altered PTPN22 expression and elevated autoimmune risk across studied conditions. A meta-analysis of immune thrombocytopenia found GG homozygotes 1.5× more susceptible than CC carriers. In Chinese JIA cohorts, the GC/CC combined genotype reached OR=2.15 — suggesting dose-dependent risk. In European populations, GG homozygotes carry both copies of the PTPN22 risk haplotype (with or without R620W), making this genotype the highest-risk combination at the PTPN22 locus.