rs10050860 — ERAP1 D575N

Missense variant (Asp575Asn) in ERAP1; the protective T allele (Asn575) is co-protective with rs30187 Arg528, with combined homozygous protective state conferring 3-4x lower ankylosing spondylitis risk in HLA-B27-positive individuals

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ERAP1 D575N — A Secondary Dial in the Peptide-Trimming Machine

Your immune system runs a continuous quality-control operation inside every cell. Proteins are constantly degraded, and small fragments — peptides — are trimmed to the correct 8-10 amino acid length11 trimmed to the correct 8-10 amino acid length
a precisely sized peptide is required for stable binding to MHC class I molecules on the cell surface; peptides that are too long or too short cannot bind and are discarded by ERAP1 (Endoplasmic Reticulum Aminopeptidase 1) before being loaded onto HLA class I display platforms. This curated peptide sample is then presented on the cell surface for inspection by patrolling CD8+ T cells — the checkpoint that determines whether a cell is "self" or dangerous.

The D575N variant changes a single amino acid in ERAP1. This substitution does not knock out the enzyme, but it measurably alters trimming efficiency — and in individuals carrying the HLA-B27 antigen, those alterations compound into a meaningful shift in ankylosing spondylitis risk. D575N's effect is context-dependent: it acts synergistically with the more powerful K528R variant (rs30187) to define one of the most well-characterized ERAP1 risk haplotypes in human genetics.

The Mechanism

Biochemical characterization of naturally occurring ERAP1 variants shows that Asp575 confers modestly lower trimming activity compared to Asn575, but critically, the magnitude of this effect depends strongly on residue 528 (the K528R variant, rs30187). Functional epistasis studies22 Functional epistasis studies
Evnouchidou et al. 2014: combined effects of ankylosing spondylitis-associated ERAP1 polymorphisms outside the catalytic and peptide-binding sites on the processing of natural HLA-B27 ligands. J Biol Chem, 2014 established the activity hierarchy: Arg528/Asp575 < Lys528/Asp575 < Arg528/Asn575 < Lys528/Asn575.

HLA-B27 is unusual among HLA class I alleles: it preferentially presents longer, arginine-terminated peptides. ERAP1 over-trimming of HLA-B27 ligands can generate a mis-edited peptide repertoire that triggers autoimmune T cell responses and/or drives HLA-B27 heavy chain misfolding and endoplasmic reticulum stress. Both high-activity and low-activity ERAP1 allotypes can create pathogenic peptide landscapes depending on the specific HLA alleles present.

The Evidence

ERAP1 haplotype and AS susceptibility. The foundational haplotype study by Evans et al. 200933 Evans et al. 2009
Association of a specific ERAP1/ARTS1 haplotype with disease susceptibility in ankylosing spondylitis. Arthritis Rheum, 2009 identified a three-SNP haplotype — rs27044/rs10050860/rs30187 coded as CCT — as strongly associated with increased AS risk (pooled OR=1.81, 95% CI 1.46-2.24, P=7×10⁻⁸ across three Canadian cohorts). The rs10050860 C allele (Asp575) is the risk allele in this haplotype.

Meta-analytic confirmation. A meta-analysis found that the rs10050860 T allele (Asn575) was significantly protective against AS in European populations, with an OR=0.724 (95% CI 0.665-0.787, P<1×10⁻¹⁰)44 OR=0.724 (95% CI 0.665-0.787, P<1×10⁻¹⁰)
Associations between ERAP1 polymorphisms and ankylosing spondylitis susceptibility: a meta-analysis. Arthritis Care Res, 2011.

Co-protective state with rs30187. When both rs10050860 T (Asn575) and rs30187 C (Lys528) are inherited together, the combined protective effect on AS risk is substantial. In HLA-B27-positive individuals, this double-protective state reduces AS risk approximately 3-4 fold55 this double-protective state reduces AS risk approximately 3-4 fold
Evans et al. 2011: HLA-B27-positive individuals homozygous for protective ERAP1 alleles had substantially lower AS risk than those carrying risk alleles at either or both ERAP1 loci. Nat Genet, 2011.

Functional ranking. Proteomics-level studies of ERAP1 variant combinations showed that while K528R (rs30187) is the dominant contributor to HLA-B27 peptidome shaping, D575N amplifies the K528R effect. Ranking studies66 Ranking studies
Kochan et al. 2018, ranking the contribution of AS-associated ERAP1 polymorphisms to shaping the HLA-B27 peptidome noted that D575N's contribution to the HLA-B27 peptidome changes — while smaller than K528R's — is consistently directional and adds to the overall allotype effect.

Important caveat on independent effect. A subset of the rs10050860 signal may be attributable to strong linkage disequilibrium with a nearby splice-altering variant, rs7063, which influences ERAP1 protein levels rather than catalytic function. This does not invalidate the D575N finding — the functional studies above directly demonstrate biochemical effects — but it means the full AS association magnitude at this locus may reflect a combination of coding and regulatory mechanisms.

Practical Implications

On its own, the C allele at rs10050860 (Asp575) does not cause disease. The clinical significance of this variant is nearly entirely contingent on your HLA-B27 status and on your rs30187 genotype.

If you carry HLA-B27, the C allele at rs10050860 (particularly if combined with the T allele at rs30187) represents the risk configuration — the ERAP1 allotype that most strongly shifts the HLA-B27 peptidome toward arthritogenic states. Early recognition of ankylosing spondylitis symptoms matters: the disease is effectively managed with NSAIDs and biologics when caught early, but causes irreversible spinal fusion when untreated for years.

If you are homozygous TT at rs10050860 and carry the CC genotype at rs30187 (Lys528), this double-protective state confers substantially reduced AS risk compared to the risk haplotype.

Interactions

rs10050860 × rs30187 (K528R): Same-gene functional epistasis. The effects of D575N and K528R are not additive — they interact. The activity hierarchy depends on the combination of residues at both positions. This interaction is the strongest rationale for analyzing both variants together in a compound action context.

rs10050860 × HLA-B27: Disease-determining epistasis. Like all ERAP1 coding variants, D575N's contribution to AS risk operates exclusively through its interaction with HLA-B27. In HLA-B27-negative individuals, the C vs T genotype at rs10050860 has no meaningful AS association. The clinical weight of this variant should be interpreted entirely in the context of HLA-B27 status.

rs10050860 in the ERAP1 haplotype system. ERAP1 has been catalogued into 10+ naturally occurring haplotypes (Hap1-Hap10) defined by combinations of variants including rs30187, rs10050860, rs27044, rs27524, and others. The predominant risk haplotype (MKDRQ: Met349-Lys528-Asp575-Arg725-Gln730) is defined partly by D (Asp575, rs10050860 C allele). The predominant protective haplotype (VRNQE) carries N575 (rs10050860 T allele). Haplotype-level analysis provides a more complete picture than individual SNP analysis for ERAP1 allotype classification.

Genotype Interpretations

What each possible genotype means for this variant.

TT Asn575 Homozygous Beneficial

Both copies carry the protective Asn575 form of ERAP1, substantially reducing AS risk particularly when combined with the Lys528 allele at rs30187

You carry two copies of the T allele at rs10050860 (Asn575 homozygous), the least common genotype globally (approximately 4% of people; higher in European populations at ~5%). This genotype represents the most protective ERAP1 configuration at this position. When inherited together with the Lys528 protective allele (rs30187 CC genotype), the combined ERAP1 allotype confers approximately 3-4 times lower AS risk in HLA-B27-positive individuals compared to the risk haplotype. This variant represents part of the VRNQE-type protective ERAP1 haplotype that consistently shows inverse association with AS across studied populations.

CT Asp575Asn Heterozygous Intermediate

One copy of the protective Asn575 allele provides partial reduction in ERAP1-related ankylosing spondylitis risk

You carry one copy of the protective T allele (Asn575) and one copy of the risk C allele (Asp575) at rs10050860. This heterozygous genotype is present in approximately 31% of people globally. The T allele provides partial protective buffering against ERAP1-related AS and spondyloarthropathy risk, particularly in combination with any protective alleles at rs30187. As with CC, the clinical relevance of this variant is contingent on your HLA-B27 status — in HLA-B27-negative individuals, ERAP1 genotype has minimal independent AS risk.

CC Asp575 Homozygous High Risk

Both copies carry the Asp575 risk form of ERAP1, associated with elevated ankylosing spondylitis risk in HLA-B27-positive individuals

The Asp575 form of ERAP1 (C allele, rs10050860) is coded by the major/reference allele globally.

The AS risk from CC genotype alone is modest in the absence of HLA-B27. But in HLA-B27-positive individuals, ERAP1 genotype is a significant secondary determinant of AS risk — the combination of risk ERAP1 alleles plus HLA-B27 generates 3-4 times higher AS risk than the combination of protective ERAP1 alleles plus HLA-B27. The CC genotype at rs10050860, particularly when also carrying the CT or TT risk genotype at rs30187, represents the highest-risk ERAP1 configuration studied.

The rs10050860 C allele is the risk allele in the MKDRQ haplotype (rs27044/rs10050860/rs30187: Q730/D575/K528), the haplotype with the strongest positive AS association (OR=1.81 in Canadian cohorts).