What you carry at this position in your DNA and what research says about it.
Severe COVID-19 Risk: 8/10 evidence, 22 publications.
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Sample genotype (not yours): C/C
Typical Risk of Severe COVID-19
This genotype is associated with a lower, typical risk of severe respiratory complications from COVID-19. It is also linked to slightly lower risks of pancreatic cancer but a higher likelihood of colon polyps.
What this genotype means: Lower risk of severe COVID-19 complications; Slightly lower risk of pancreatic cancer; Slightly higher risk of colon polyps.
Sample genotype (not yours): A/A
Increased Risk of Severe COVID-19
Carrying two copies of the A allele is linked to a higher risk of severe COVID-19 respiratory failure. It is also associated with slightly higher risks of pancreatic cancer and elevated TSH levels.
What this genotype means: Higher risk of severe COVID-19 respiratory failure; Slightly higher risk of pancreatic cancer; Slightly higher baseline TSH levels.
Sample genotype (not yours): C/A
Slightly Increased Risk of Severe COVID-19
Carrying one copy of the A allele is associated with a slightly elevated risk of severe COVID-19 complications. It also represents an intermediate profile for pancreatic cancer and colon polyp risks.
What this genotype means: Slightly higher risk of severe COVID-19; Intermediate risk of pancreatic cancer; Intermediate risk of colon polyps.
Gene function and biological role
Gene Function: The ABO gene encodes a glycosyltransferase enzyme that determines an individual's ABO blood group by modifying carbohydrates on red blood cells and other tissues. Beyond blood typing, this gene plays a critical role in cardiovascular health, inflammation, and susceptibility to infectious diseases [1]. Variations in the ABO gene influence circulating levels of key coagulation factors, such as Von Willebrand factor, which directly impacts blood clotting and stroke risk [2]. Additionally, the gene is associated with systemic inflammatory markers and cellular adhesion molecules that modulate how the immune system responds to pathogens [3].
Variant Impact: The rs657152 variant is an intronic change located within the ABO gene on chromosome 9. This genetic marker is in strong linkage disequilibrium with the primary genetic determinants of the ABO blood group system [1]. The A allele of this variant is strongly linked to non-O blood groups, particularly blood group A, which influences cellular susceptibility to viral entry and immune recognition [4]. Conversely, the C allele is associated with blood group O, which is often protective against certain severe infections but carries different baseline metabolic characteristics [5].
Key Insight: This variant was one of the very first genetic markers linked to severe COVID-19 respiratory failure in early 2020 genome-wide studies.
Location: ABO. Chromosome 9 · 9q34.2 · 133.3 Mb
Estimated prevalence by population
Global 37.0%; European 40.1%; African 31.7%; East Asian 39.1%; South Asian 30.4%; Americas 48.6%; Ashkenazi 31.5%; Finnish 27.3%; Middle Eastern 43.1%; Amish 9.2%.
Estimated CC genotype frequency.
Global 47.2%; European 46.5%; African 49.2%; East Asian 46.9%; South Asian 49.5%; Americas 42.2%; Ashkenazi 49.2%; Finnish 49.9%; Middle Eastern 45.1%; Amish 42.3%.
Estimated CA genotype frequency.
Global 15.8%; European 13.5%; African 19.1%; East Asian 14.1%; South Asian 20.2%; Americas 9.2%; Ashkenazi 19.2%; Finnish 22.8%; Middle Eastern 11.8%; Amish 48.4%.
Estimated AA genotype frequency.
Showing effects for C/C genotype
Immunity & Inflammation
Infection Susceptibility & Resistance
COVID-19 Severity. Evidence: 8/10. Source: PMID 32558485. Typical Risk.
Inflammatory & Circulating Protein Markers
Systemic Inflammation. Evidence: 4/10. Source: PMID 23251661. Typical IL-6.
Cancer & Oncology
Gastrointestinal Cancers
Pancreatic Cancer. Evidence: 4/10. Source: PMID 23816557. Typical Risk.
Colorectal Cancer
Colon Polyps. Evidence: 6/10. Source: PMID 34594039. Increased Risk.
Endocrine & Reproductive
Hormone Levels & Endocrine Regulation
Thyroid Function. Evidence: 4/10. Source: PMID 23408906. Typical TSH.
Estrogen Levels. Evidence: 8/10. Source: PMID 32042192. Higher Estradiol.
Showing effects for A/A genotype
COVID-19 Severity. Evidence: 8/10. Source: PMID 32558485. ~1.3x Higher Risk.
Systemic Inflammation. Evidence: 4/10. Source: PMID 23251661. Higher IL-6.
Pancreatic Cancer. Evidence: 4/10. Source: PMID 23816557. Increased Risk.
Colon Polyps. Evidence: 6/10. Source: PMID 34594039. Typical Risk.
Thyroid Function. Evidence: 4/10. Source: PMID 23408906. Higher TSH.
Estrogen Levels. Evidence: 8/10. Source: PMID 32042192. Lower Estradiol.
Showing effects for C/A genotype
COVID-19 Severity. Evidence: 8/10. Source: PMID 32558485. Slightly Higher Risk.
Pancreatic Cancer. Evidence: 4/10. Source: PMID 23816557. Slightly Higher Risk.
Colon Polyps. Evidence: 6/10. Source: PMID 34594039. Slightly Higher Risk.
Estrogen Levels. Evidence: 8/10. Source: PMID 32042192. Typical Estradiol.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Carrying two copies of the C allele is the most common genetic profile globally. Large-scale genome-wide association studies have demonstrated that this genotype is protective against severe respiratory failure during COVID-19 infections compared to carriers of the A allele [1]. This protective effect is closely tied to the biological characteristics of blood group O, which is highly correlated with this genetic signature [2]. However, this genotype is also associated with higher circulating levels of estradiol, which can influence bone mineral density and hormonal balance [3]. Additionally, research suggests a slightly elevated risk for developing colon polyps, requiring standard adherence to routine screening guidelines [4].
Lower risk of severe COVID-19 complications; Slightly lower risk of pancreatic cancer; Slightly higher risk of colon polyps.
Sample genotype: AA (Homozygous)
Having two copies of the A allele is associated with the highest genetic risk at this locus for severe respiratory complications and mortality from COVID-19 [1]. This variant is strongly linked to non-O blood groups (such as blood group A), which exhibit higher levels of cell-adhesion molecules and altered immune responses to certain viral pathogens [2]. Research also indicates that this genotype is associated with a slightly higher risk of pancreatic ductal adenocarcinoma [3]. Furthermore, individuals with this profile tend to have higher baseline levels of thyroid-stimulating hormone (TSH), which can be a marker of subtle differences in thyroid regulation [4]. Conversely, this genotype is associated with a lower risk of developing colon polyps [5].
Higher risk of severe COVID-19 respiratory failure; Slightly higher risk of pancreatic cancer; Slightly higher baseline TSH levels.
Sample genotype: CA (Heterozygous)
This heterozygous genotype represents a blend of the major and minor allele traits. Having one copy of the A allele correlates with a slightly increased susceptibility to severe respiratory symptoms and hospitalization from COVID-19 [1]. This genetic link is mediated by the ABO blood group system, where non-O blood groups show different patterns of viral interaction and inflammatory response [2]. Individuals with this genotype may also have slightly higher baseline levels of systemic inflammatory markers like interleukin-6 [3]. On the other hand, the presence of one C allele maintains a moderate risk profile for colon polyps and intermediate estradiol levels [4].
Slightly higher risk of severe COVID-19; Intermediate risk of pancreatic cancer; Intermediate risk of colon polyps.
Variants with shared genetic architecture
rs507666 · ABO Gene · Chr 9 · Heart Disease Risk
rs550057 · ABO Gene · Chr 9 · COVID-19 Severity
rs495828 · ABO Gene · Chr 9 · Blood Clot Risk
Genomewide Association Study of Severe Covid-19 with Respiratory Failure.
Genetic regulation of serum phytosterol levels and risk of coronary artery disease.
A cross-population atlas of genetic associations for 220 human phenotypes.
Content updated August 2026.
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