PTPN22 rs2476602: Autoimmunity Risk and the R620W Variant
The rs2476602 variant in the PTPN22 gene is a widely studied single-nucleotide polymorphism that alters an amino acid in the lymphoid tyrosine phosphatase enzyme. Carrying the alternative T allele is statistically associated with a higher susceptibility to several autoimmune conditions, including rheumatoid arthritis, type 1 diabetes, and systemic lupus erythematosus. However, inheriting this variant is not diagnostic and represents only one component in a complex web of genetic and environmental influences.
What each genotype means
Typical autoimmune predisposition
You carry two copies of the common C allele at this position. This genotype is not associated with elevated genetic susceptibility to autoimmune disorders like rheumatoid arthritis or type 1 diabetes linked to this locus. Your baseline risk for these conditions is comparable to the standard population rate.
Found in approximately 84% to 86% of European populations and virtually 100% of East Asian and African populations.
Moderately increased autoimmune predisposition
You have one copy of the T risk allele and one copy of the C allele. In published studies, carrying one risk allele is associated with a moderate increase in relative susceptibility to autoimmune conditions including rheumatoid arthritis, type 1 diabetes, and systemic lupus erythematosus. This is a statistical risk factor and does not mean that you will develop an autoimmune disorder.
Carried by approximately 13% to 15% of individuals of European ancestry, but rarely observed in East Asian or African populations.
Elevated autoimmune predisposition
You carry two copies of the T risk allele at this variant. Multiple studies have reported that having two risk alleles confers a stronger statistical predisposition to autoimmune diseases, such as rheumatoid arthritis and type 1 diabetes, compared to non-carriers. Genetic predisposition is only one component of disease risk, and most individuals with this genotype do not develop these conditions.
Carried by roughly 0.5% to 1% of individuals of European descent and is extremely rare or absent in other global populations.
Genomic Location and the R620W Variation
The single-nucleotide polymorphism rs2476602 (historically documented in literature as c.1858C>T or C1858T) is located on chromosome 1 within exon 14 of the PTPN22 (Protein Tyrosine Phosphatase Non-Receptor Type 22) gene. This missense mutation changes a single nucleotide from cytosine (C) to thymine (T). At the protein level, this nucleotide substitution replaces the amino acid arginine with tryptophan at position 620, an alteration commonly designated as R620W. This amino acid switch occurs in a critical proline-rich motif of the encoded lymphoid phosphatase protein, altering how the enzyme binds to intracellular regulatory partners, including the C-terminal Src kinase (CSK).
Biological Role of PTPN22 in Immune Signaling
The PTPN22 gene codes for lymphoid-specific tyrosine phosphatase (LYP), an intracellular enzyme expressed primarily in immune cells such as T lymphocytes, B lymphocytes, and neutrophils. Under normal physiological conditions, LYP acts as an important negative regulator of antigen receptor signaling, dephosphorylating key kinases to prevent excessive immune activation. The R620W substitution encoded by the rs2476602 alternative allele disrupts standard protein-protein interactions, altering the threshold for immune cell activation and selection. Research indicates this disruption can impair central and peripheral tolerance mechanisms, allowing potentially autoreactive lymphocytes to escape elimination and circulate in peripheral tissues.
Autoimmune Disease Associations and Evidence
Large-scale genome-wide association studies (GWAS) and systematic meta-analyses have established rs2476602 as one of the most prominent non-HLA genetic risk factors for multiple autoimmune disorders. Carriers of the T allele demonstrate increased statistical odds of developing rheumatoid arthritis (RA), type 1 diabetes mellitus (T1D), systemic lupus erythematosus (SLE), and juvenile idiopathic arthritis. Interestingly, while the variant increases susceptibility across systemic and organ-specific autoimmune conditions, some studies have noted neutral or paradoxically divergent associations with certain intestinal inflammatory disorders like Crohn's disease. Despite strong statistical correlations, the effect size remains modest, operating co-dominantly alongside diverse polygenic and environmental risk factors.
Population Distribution and Ancestry Patterns
The distribution of rs2476602 exhibits dramatic divergence across ancestral populations. The minor T allele is observed primarily in populations of European ancestry, where its frequency generally ranges between 5% and 15% (with an average minor allele frequency around 0.08, trending higher in Northern Europe than Southern Europe). Conversely, the variant allele is virtually absent or found at extremely low frequencies (less than 0.001) in East Asian and African populations. Consequently, the statistical autoimmune risks attributed to this specific SNP are primarily applicable and measurable within European cohorts, highlighting the population-specific architecture of complex genetic traits.
Understanding Your Results in Context
Discovering an rs2476602 variant on a direct-to-consumer genetic test does not mean that an individual has an autoimmune disease or will inevitably develop one. Like most complex health predispositions, autoimmune conditions arise from an intricate interplay of dozens or hundreds of genetic loci combined with environmental triggers, infections, microbiome composition, and lifestyle factors. Genetic findings for rs2476602 cannot be used for standalone clinical diagnosis, prognosis, or therapeutic decisions. Individuals with personal health concerns, unexplained joint pain, or a family history of autoimmune illness should consult a qualified physician or genetic counselor for comprehensive clinical evaluation.
How common is this variant?
The minor T allele frequency is approximately 0.08 in European populations, with higher frequencies reported in Northern Europe, but it is virtually absent (frequency below 0.001) in East Asian and African populations.
Frequently asked questions
Does having the rs2476602 T allele mean I will get an autoimmune disease?
No. The rs2476602 variant confers a modest statistical predisposition rather than a direct clinical diagnosis. Most individuals who carry the T allele never develop an autoimmune condition because disease onset requires multiple additional genetic, environmental, and immune factors.
Why is the rs2476602 variant called R620W?
The label R620W refers to the specific change in the protein product. The single nucleotide change at rs2476602 causes the amino acid arginine (abbreviated as R) to be replaced by tryptophan (abbreviated as W) at position 620 of the LYP enzyme.
Can this genetic variant predict my response to medications?
Current clinical guidelines do not recommend altering medication regimens based on rs2476602 genotype alone. Always discuss pharmacological therapies, dosing, and treatment plans with your prescribing physician or a pharmacist.
Why is this variant common in Europeans but rare in other ancestries?
Allele frequencies often differ across global populations due to ancestral demographic history, genetic drift, and natural selection. The rs2476602 T allele arose or expanded in frequency in ancestral European populations while remaining largely absent in African and Asian ancestral lineages.
Sources & further reading
Educational information only, last refreshed 9/13/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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