What you carry at this position in your DNA and what research says about it.
Ankylosing Spondylitis Risk: 8/10 evidence, 40 publications.
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Sample genotype (not yours): T/T
Double Risk of Ankylosing Spondylitis
Carrying two copies of the T allele is associated with a twofold increase in the risk of developing ankylosing spondylitis. Conversely, this genotype is linked to slightly lower blood pressure and a reduced risk of hypertension.
What this genotype means: Twofold higher risk of ankylosing spondylitis; Slightly lower blood pressure; Reduced risk of hypertension.
Sample genotype (not yours): C/C
Typical Low Risk of Ankylosing Spondylitis
Carrying two copies of the C allele provides protection against ankylosing spondylitis, maintaining a typical low risk of about 0.1%. However, it is associated with slightly higher blood pressure and hypertension risk.
What this genotype means: Typical low risk (0.1%) of ankylosing spondylitis; Slightly higher blood pressure; Slightly increased risk of hypertension.
Sample genotype (not yours): T/C
Moderately Increased Ankylosing Spondylitis Risk
Carrying one copy of the T allele is linked to a 1.4-fold higher risk of developing ankylosing spondylitis. It also represents an intermediate profile for blood pressure and hypertension risk.
What this genotype means: 1.4x higher risk of ankylosing spondylitis; Intermediate blood pressure levels; Slightly elevated hypertension risk.
Gene function and biological role
Gene Function: The ERAP1 gene encodes endoplasmic reticulum aminopeptidase 1, an enzyme essential for processing proteins into smaller peptide fragments [1]. These trimmed peptides are then loaded onto major histocompatibility complex class I molecules, which present them on the cell surface to immune cells [1]. This presentation is a critical step in helping the immune system distinguish between the body's own cells and foreign invaders [2]. Beyond its immunological role, ERAP1 also helps regulate blood pressure by degrading angiotensin II, a hormone that constricts blood vessels [3]. Consequently, variations in this gene can influence both autoimmune susceptibility and cardiovascular health.
Variant Impact: A missense mutation in the ERAP1 gene, rs30187 alters the amino acid at position 528 from lysine to arginine [1]. This specific change directly impacts the enzyme's trimming efficiency, altering how effectively it processes peptide antigens [1]. The lysine-encoding T allele produces a highly active enzyme, whereas the arginine-encoding C allele results in reduced trimming activity [4]. This difference in peptide processing alters the repertoire of antigens presented to the immune system, particularly in individuals carrying the HLA-B27 tissue type. Additionally, the altered enzyme activity affects the degradation of vasoactive peptides, thereby influencing blood pressure regulation [3].
Key Insight: This variant acts as a genetic trade-off, where the allele that protects against a severe spinal autoimmune condition slightly increases the risk of high blood pressure.
Location: ERAP1. Chromosome 5 · 5q15 · 96.8 Mb
Estimated prevalence by population
Global 14.2%; European 11.7%; African 15.6%; East Asian 23.7%; South Asian 17.0%; Americas 16.3%; Ashkenazi 19.2%; Finnish 12.5%; Middle Eastern 24.0%; Amish 30.4%.
Estimated TT genotype frequency.
Global 46.6%; European 45.0%; African 47.8%; East Asian 50.0%; South Asian 48.5%; Americas 48.2%; Ashkenazi 49.2%; Finnish 45.7%; Middle Eastern 50.0%; Amish 49.5%.
Estimated TC genotype frequency.
Global 39.2%; European 43.3%; African 36.5%; East Asian 26.4%; South Asian 34.5%; Americas 35.5%; Ashkenazi 31.5%; Finnish 41.8%; Middle Eastern 26.0%; Amish 20.1%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Immunity & Inflammation
Autoimmune Diseases
Ankylosing Spondylitis. Evidence: 8/10. Source: PMID 21743469. 2x Higher Risk.
Cardiovascular & Metabolic
Hypertension
Systolic Blood Pressure. Evidence: 7/10. Source: PMID 33230300. Slightly Lower.
Diastolic Blood Pressure. Evidence: 7/10. Source: PMID 33230300. Slightly Lower.
Hypertension. Evidence: 7/10. Source: PMID 33230300. Reduced Risk.
Blood Cell & Iron Traits
Mean Platelet Volume. Evidence: 7/10. Source: PMID 32888493. Slightly Lower.
Showing effects for C/C genotype
Ankylosing Spondylitis. Evidence: 8/10. Source: PMID 21743469. Typical Low Risk.
Systolic Blood Pressure. Evidence: 7/10. Source: PMID 33230300. Slightly Higher.
Diastolic Blood Pressure. Evidence: 7/10. Source: PMID 33230300. Slightly Higher.
Hypertension. Evidence: 7/10. Source: PMID 33230300. Increased Risk.
Mean Platelet Volume. Evidence: 7/10. Source: PMID 32888493. Slightly Higher.
Showing effects for T/C genotype
Ankylosing Spondylitis. Evidence: 8/10. Source: PMID 21743469. 1.4x Higher Risk.
Systolic Blood Pressure. Evidence: 7/10. Source: PMID 33230300. Intermediate.
Diastolic Blood Pressure. Evidence: 7/10. Source: PMID 33230300. Intermediate.
Hypertension. Evidence: 7/10. Source: PMID 33230300. Slightly Increased.
Mean Platelet Volume. Evidence: 7/10. Source: PMID 32888493. Typical.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Susceptibility to ankylosing spondylitis is significantly elevated in individuals carrying two copies of the T allele, particularly when the HLA-B27 gene is also present [1]. This genotype encodes the highly active lysine form of the ERAP1 enzyme, which trims peptides to a length that easily binds to HLA-B27, triggering an autoimmune inflammatory response in the joints. Studies across multiple populations, including Caucasian and East Asian cohorts, consistently replicate this elevated risk. On the cardiovascular side, the highly active enzyme more efficiently degrades angiotensin II, which helps keep blood vessels relaxed [2]. As a result, individuals with this genotype tend to have slightly lower systolic and diastolic blood pressure [2]. They also exhibit a lower overall risk of developing essential hypertension [2]. Despite these cardiovascular benefits, the substantial increase in autoimmune risk makes this genotype unfavorable overall [3].
Twofold higher risk of ankylosing spondylitis; Slightly lower blood pressure; Reduced risk of hypertension.
Sample genotype: CC (Homozygous)
Protection against the development of ankylosing spondylitis is highly pronounced in individuals with two copies of the C allele, resulting in a typical baseline risk of just 0.1% [1]. This genotype encodes the arginine variant of the ERAP1 enzyme, which has reduced trimming efficiency and fails to generate the specific peptides that trigger spinal joint autoimmunity [2]. Multiple large-scale genetic studies confirm that individuals with this genotype are at a significantly lower risk for inflammatory joint diseases. However, this reduced enzyme activity also means angiotensin II is degraded less efficiently, leaving more of this vessel-constricting hormone in circulation [3]. Consequently, individuals with this genotype experience a small but measurable increase in both systolic and diastolic blood pressure [3]. This translates to a slightly higher susceptibility to essential hypertension over time [3]. Because the autoimmune protection is highly significant, this genotype is considered favorable overall [1].
Typical low risk (0.1%) of ankylosing spondylitis; Slightly higher blood pressure; Slightly increased risk of hypertension.
Sample genotype: TC (Heterozygous)
Inheriting one T allele and one C allele results in a moderate increase in the risk of ankylosing spondylitis [1]. The presence of the T allele leads to intermediate levels of ERAP1 enzyme activity, which moderately increases the presentation of inflammatory peptides to the immune system [2]. This intermediate activity translates to a 1.4-fold higher likelihood of spinal joint inflammation compared to the baseline population [3]. On the cardiovascular front, this genotype is associated with intermediate blood pressure levels [4]. The balance between the lysine and arginine variants of the enzyme provides moderate degradation of angiotensin II [4]. Consequently, the risk of developing hypertension is only slightly elevated compared to those with the protective cardiovascular genotype [4]. Overall, the moderate increase in autoimmune risk is the primary health factor for carriers [3].
1.4x higher risk of ankylosing spondylitis; Intermediate blood pressure levels; Slightly elevated hypertension risk.
Variants with shared genetic architecture
rs27044 · ERAP1 Gene · Chr 5 · Spondylitis Risk
rs17482078 · ERAP1 Gene · Chr 5 · Inflammatory Disease Risk
rs26653 · ERAP1 Gene · Chr 5 · Autoimmune Joint Risk
Functional variants of ERAP1 gene are associated with HLA-B27 positive spondyloarthritis.
Content updated August 2026.
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