What you carry at this position in your DNA and what research says about it.
Blood Type Disease Risk: 9/10 evidence, 40 publications.
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Sample genotype (not yours): C/C
Non-O Blood Type and Higher Disease Risks
A non-O blood type (A, B, or AB) is indicated by this genetic profile. It is associated with an elevated risk of blood clots, pancreatic cancer, and type 2 diabetes.
What this genotype means: Non-O blood type (A, B, or AB); Higher risk of blood clots and pancreatic cancer; Slightly higher risk of type 2 diabetes.
Sample genotype (not yours): C/T
Non-O Blood Type and Moderately Higher Risks
A non-O blood type is typically indicated by this genetic profile. It is linked to a moderately increased risk of pancreatic cancer and venous blood clots.
What this genotype means: Non-O blood type; Moderately higher risk of pancreatic cancer; Moderately higher risk of blood clots.
Sample genotype (not yours): T/T
Blood Type O and Lower Disease Risks
Blood type O is indicated by this genetic profile. It is associated with a lower risk of blood clots, pancreatic cancer, and type 2 diabetes.
What this genotype means: Blood type O; Lower risk of blood clots and pancreatic cancer; Slightly higher risk of Graves disease.
Gene function and biological role
Gene Function: The ABO gene encodes the glycosyltransferase enzyme responsible for determining an individual's ABO blood group [1]. This enzyme modifies carbohydrate antigens on the surface of red blood cells and other tissues [1]. Depending on the specific genetic sequence, the enzyme is either fully functional, producing A or B antigens, or inactive, resulting in the O blood type [1]. Beyond blood transfusions, these surface antigens play a critical role in cell-to-cell communication and immune responses [2]. Consequently, the ABO gene is heavily linked to cardiovascular health, blood clotting, and susceptibility to various infectious diseases and cancers [2].
Variant Impact: The rs505922 variant is an intronic single nucleotide polymorphism located within the ABO gene that serves as a strong genetic marker for blood type [1]. Specifically, the T allele is in tight linkage disequilibrium with the deletion that inactivates the ABO enzyme, thereby tagging the O blood type [1]. Conversely, the C allele is associated with non-O blood types, which feature active A or B antigens on cell surfaces [1]. This molecular difference alters how cells interact with clotting factors and inflammatory proteins in the bloodstream [3]. As a result, this single genetic change significantly influences an individual's risk profile for blood clots, pancreatic cancer, and metabolic conditions [3].
Key Insight: This variant acts as a genetic proxy for your ABO blood group, with the T allele representing blood type O and the C allele representing non-O blood types. Your blood type significantly influences your risk for blood clots and pancreatic cancer due to how blood group antigens interact with clotting factors and inflammatory proteins.
Location: ABO. Chromosome 9 · 9q34.2 · 133.3 Mb
Origin Story: The evolutionary persistence of different ABO blood groups is widely believed to be driven by natural selection and resistance to infectious diseases. For instance, blood type O, tagged by the T allele, is historically associated with increased survival and protection against severe malaria, which likely helped maintain its high frequency in populations where malaria was endemic.
Estimated prevalence by population
Global 12.8%; European 11.8%; African 12.6%; East Asian 14.8%; South Asian 18.9%; Americas 7.5%; Ashkenazi 17.0%; Finnish 21.2%; Middle Eastern 10.4%; Amish 41.5%.
Estimated CC genotype frequency.
Global 45.3%; European 45.1%; African 45.8%; East Asian 47.3%; South Asian 49.2%; Americas 39.7%; Ashkenazi 48.4%; Finnish 49.7%; Middle Eastern 43.7%; Amish 45.8%.
Estimated CT genotype frequency.
Global 41.9%; European 43.2%; African 41.6%; East Asian 37.9%; South Asian 31.9%; Americas 52.8%; Ashkenazi 34.6%; Finnish 29.1%; Middle Eastern 45.8%; Amish 12.7%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Cancer & Oncology
Gastrointestinal Cancers
Pancreatic Cancer. Evidence: 8/10. Source: PMID 19648918. ~1.5x Increased Risk.
Cardiovascular & Metabolic
Coagulation & Clotting
Venous Thromboembolism. Evidence: 9/10. Source: PMID 19278955. ~1.8x Increased Risk.
Diabetes & Glycemic Traits
Type 2 Diabetes. Evidence: 9/10. Source: PMID 29358691. Slightly Increased.
Vascular Health & Aneurysm
Arterial Disease. Evidence: 7/10. Source: PMID 31285632. Slightly Increased.
Immunity & Inflammation
Infection Susceptibility & Resistance
COVID-19 Severity. Evidence: 8/10. Source: PMID 35848942. Increased Risk.
Autoimmune Diseases
Graves' Disease. Evidence: 6/10. Source: PMID 21841780. Typical Risk.
Showing effects for C/T genotype
Pancreatic Cancer. Evidence: 8/10. Source: PMID 19648918. ~1.2x Increased Risk.
Venous Thromboembolism. Evidence: 9/10. Source: PMID 19278955. Increased Risk.
COVID-19 Severity. Evidence: 8/10. Source: PMID 35848942. Slightly Increased.
Graves' Disease. Evidence: 6/10. Source: PMID 21841780. Slightly Increased.
Showing effects for T/T genotype
Pancreatic Cancer. Evidence: 8/10. Source: PMID 19648918. Typical Risk.
Venous Thromboembolism. Evidence: 9/10. Source: PMID 19278955. Typical Risk.
Type 2 Diabetes. Evidence: 9/10. Source: PMID 29358691. Typical Risk.
Arterial Disease. Evidence: 7/10. Source: PMID 31285632. Typical Risk.
COVID-19 Severity. Evidence: 8/10. Source: PMID 35848942. Typical Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
A non-O blood type, such as A, B, or AB, strongly correlates with this genetic profile [1]. Research shows that those with non-O blood types have higher circulating levels of von Willebrand factor and other clotting proteins, which increases the risk of venous thromboembolism [2]. This genotype is also associated with a roughly 1.5-fold increased risk of developing pancreatic cancer compared to those with blood type O [3]. Furthermore, large-scale genetic studies have linked this profile to slightly higher rates of type 2 diabetes and peripheral arterial disease [4]. On the other hand, this genotype appears to offer some protection against Graves' disease, an autoimmune thyroid condition [5]. Overall, maintaining a heart-healthy lifestyle and avoiding smoking can help mitigate these elevated cardiovascular and cancer risks.
Non-O blood type (A, B, or AB); Higher risk of blood clots and pancreatic cancer; Slightly higher risk of type 2 diabetes.
Sample genotype: CT (Heterozygous)
Inheriting one C allele and one T allele typically results in a non-O blood type, as the C allele is dominant over the O-associated T allele [1]. This heterozygous profile is associated with a 1.2-fold increased risk of pancreatic cancer compared to individuals with blood type O [2]. The presence of the C allele also leads to higher levels of clotting factors, moderately elevating the risk of venous thromboembolism and peripheral arterial disease [3]. Additionally, some studies suggest a slight increase in susceptibility to severe COVID-19 infections and type 2 diabetes [4]. Conversely, carrying one copy of each allele represents an intermediate risk profile for Graves' disease [5]. Focusing on routine cardiovascular health and a balanced diet is highly beneficial for individuals with this genetic makeup.
Non-O blood type; Moderately higher risk of pancreatic cancer; Moderately higher risk of blood clots.
Sample genotype: TT (Homozygous)
Blood type O is typically determined by this genetic profile, which is characterized by the absence of A and B antigens on red blood cells [1]. This genetic profile is highly protective against venous thromboembolism, as individuals with blood type O naturally have lower levels of key clotting factors [2]. It is also associated with the lowest risk of pancreatic cancer, showing a significant protective effect compared to non-O genotypes [3]. Additionally, large-scale studies have linked this genotype to lower rates of type 2 diabetes, peripheral arterial disease, and severe respiratory complications from COVID-19 [4]. However, this genotype is associated with a slightly higher susceptibility to Graves' disease, an autoimmune thyroid condition [5]. Despite this minor trade-off, the overall health profile of this genotype is highly favorable.
Blood type O; Lower risk of blood clots and pancreatic cancer; Slightly higher risk of Graves disease.
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
Association between ABO gene polymorphism (rs505922) and cancer risk: a meta-analysis.
Detailed stratified GWAS analysis for severe COVID-19 in four European populations.
Content updated August 2026.
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