PTPN22

PTPN22 rs1217414 — An Independent Autoimmune Signal Beyond R620W

The PTPN22 gene is widely known for its R620W variant (rs2476601), one of the strongest non-HLA autoimmune risk factors. But R620W is not the only
functional player in this locus. Deep sequencing and haplotype studies have revealed that multiple independent signals exist within PTPN22 |
Haplotype analysis of 37 SNPs identified two additional PTPN22 variants associated with RA independent of R620W,
each potentially influencing immune regulation through different mechanisms. rs1217414 is one such secondary variant — an intronic SNP that has been
associated with psoriasis, ankylosing spondylitis, and autoimmune conditions in populations where R620W is effectively absent.

The Mechanism

rs1217414 sits within an intron of PTPN22 at GRCh38 chromosome 1 position 113,870,044. PTPN22 is transcribed on the minus strand, so genome files
report the plus-strand alleles (G/A), while many publications report the complementary coding-strand alleles (C/T). The G allele (plus strand) corresponds
to C on the coding strand; the A allele (plus strand) corresponds to T. As an intronic variant, rs1217414 has no direct effect on protein sequence. Its
functional impact is most likely regulatory — intronic variants can affect splicing efficiency, create or destroy binding sites for splicing factors, or
alter local chromatin accessibility | Intronic variants near exon-intron boundaries or within regulatory elements can modulate mRNA splicing and
transcription factor binding, altering PTPN22 expression level or isoform ratios in immune cells.

The low LD between rs1217414 and R620W | The psoriasis study found rs2476601 showed no association when rs1217414 was significantly associated,
indicating these two signals are largely independent means this variant captures PTPN22 biology not tagged
by the classic risk allele. In populations of East Asian ancestry, where R620W is nearly absent (~1% MAF), rs1217414 represents the primary accessible
PTPN22 risk signal, explaining why multiple Chinese-population studies examined this SNP specifically.

The Evidence

The most compelling evidence comes from Smith et al. 2008 | Polymorphisms in the PTPN22 region are associated with psoriasis of early onset. Br J
Dermatol, 2008, who genotyped 647 Type I psoriasis patients and 566 controls, then replicated in a
combined dataset of 900 patients and 2,590 controls. rs1217414 demonstrated significant association (P=0.003) and the signal held when adjusted for
rs2476601, confirming independence. Crucially, R620W showed no association with psoriasis at all, while rs1217414 did — a pattern that is the inverse
of what is seen in rheumatoid arthritis, where R620W dominates.

In a Chinese Han cohort, Wang et al. 2015 | Association of PTPN22 polymorphisms and ankylosing spondylitis susceptibility. Int J Clin Exp Pathol,
2015 found the T allele (A on plus strand) conferred substantial risk for ankylosing spondylitis (OR=2.13
for heterozygotes, OR=5.79 for homozygotes) — an additive dose-response pattern. The allele frequency in controls was ~10.5%, close to the 8% MAF
in East Asian populations from dbSNP.

A large-scale Chinese Han study by Tang et al. 2016 | PTPN22 polymorphisms, but not R620W, were associated with genetic susceptibility of SLE and
RA in a Chinese Han population. Hum Immunol, 2016 found the same T allele (A plus strand) to be protective
against both SLE (OR=0.57, padj=6×10⁻⁴; 713 cases, 672 controls) and RA (OR=0.26, padj=2×10⁻⁸; 358 cases, 564 controls). This may appear contradictory
to the AS risk data, but these studies used different populations and examined different autoimmune conditions with distinct immune pathologies. The
direction of effect at non-coding regulatory variants can differ by tissue context, disease type, and LD background.

In European-Americans with SLE, Namjou et al. 2013 | PTPN22 association in SLE with respect to individual ancestry and clinical sub-phenotypes.
PLoS One, 2013 identified rs1217414 as an independent secondary signal alongside rs2476601, specifically
in European-Americans. Neither SNP showed independent association in African-Americans or Asian-Americans.

The overall picture is moderate-evidence | Evidence is replicated across multiple independent studies and populations but with inconsistent direction of
effect across conditions, preventing clinical-grade classification: this variant genuinely influences
PTPN22-mediated immune regulation, but its directional effects differ by disease context, population background, and LD architecture.

Practical Implications

If you carry one or two copies of the A allele (GA or AA genotype), your PTPN22 regulatory activity may differ from the population average in ways
that modulate autoimmune susceptibility — specifically for psoriasis and spondyloarthropathy risk. Unlike R620W, this variant does not have established
associations with rheumatoid arthritis or type 1 diabetes in European populations, so the monitoring priorities differ.

The most clinically actionable finding is the psoriasis signal: if you have a personal or family history of psoriasis, early-onset skin or joint symptoms
warrant dermatology evaluation. Psoriatic arthritis — the inflammatory joint disease that affects about 30% of people with psoriasis — often begins with
skin disease and can progress silently before joint symptoms become prominent. PTPN22 variants have also been implicated in ankylosing spondylitis, a
form of axial spondyloarthropathy; unexplained back pain with inflammatory features (morning stiffness, worsening at rest) in carriers is worth evaluating.

Interactions

The key interaction context is with rs2476601 (R620W), the primary PTPN22 variant. rs1217414 is largely independent of R620W — the two SNPs tag
different haplotypes and likely different functional mechanisms. In Europeans, someone carrying both rs1217414-A and rs2476601-A faces cumulative PTPN22
dysregulation from two independent axes. In East Asian populations where R620W is rare, rs1217414 becomes the primary PTPN22 signal.

Within the psoriasis signal, rs1217414 was found to interact with rs3789604 — carrying risk alleles at both SNPs showed stronger combined association
(P=0.002) than either alone, suggesting haplotype-level effects on PTPN22 regulation. rs3789604 is a nearby PTPN22 variant also in the database;
together these may define a psoriasis-specific haplotype distinct from the R620W haplotype that drives RA and T1D risk.