What you carry at this position in your DNA and what research says about it.
Blood Clotting and VTE Risk: 9/10 evidence, 28 publications.
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Sample genotype (not yours): G/G
Higher Risk of Blood Clots
Carrying two copies of the G allele is associated with non-O blood groups and significantly higher levels of active clotting factors. This genotype increases the risk of developing deep vein blood clots and cardiovascular complications.
What this genotype means: Elevated risk of deep vein thrombosis; Higher circulating clotting factors; Increased risk of type 2 diabetes.
Sample genotype (not yours): A/A
Typical Clotting and Lower VTE Risk
Carrying two copies of the A allele is strongly linked to blood group O, which naturally promotes faster clearance of clotting factors. This genotype provides significant protection against deep vein blood clots.
What this genotype means: Lower baseline clotting factor levels; Reduced risk of deep vein thrombosis; Typical metabolic and liver enzyme profiles.
Sample genotype (not yours): G/A
Moderately Increased Blood Clot Risk
Carrying one copy of the G allele is associated with non-O blood groups and moderately elevated levels of clotting factors. This genotype presents an intermediate risk for venous thromboembolism compared to the typical baseline.
What this genotype means: Moderately higher clotting factor levels; Slightly elevated risk of venous clots; Slightly higher type 2 diabetes risk.
Gene function and biological role
Gene Function: The ABO gene encodes glycosyltransferase enzymes that determine an individual's ABO blood group by modifying carbohydrate antigens on red blood cells and other tissues [1]. Beyond determining blood type compatibility, these enzymatic modifications influence the clearance and half-life of critical plasma proteins involved in coagulation [2]. Specifically, non-O blood group enzymes slow down the breakdown of von Willebrand factor and coagulation factor VIII, leading to higher circulating levels of these proteins [2]. Consequently, genetic variation within this gene is a major determinant of systemic blood clotting activity and cardiovascular risk profiles.
Variant Impact: The rs687621 variant is an intronic single nucleotide polymorphism located within the ABO gene that serves as a strong genetic proxy for blood group status. The A allele is in tight linkage disequilibrium with the O blood group, whereas the G allele is associated with non-O blood groups such as A, B, or AB [3]. This genetic change alters the expression and activity of the ABO transferase enzyme, directly impacting the glycosylation patterns of clotting factors in the bloodstream [2]. As a result, individuals carrying different alleles show marked differences in their baseline blood coagulation rates and susceptibility to thromboembolic events.
Key Insight: This single genetic letter determines whether your body clears clotting proteins quickly or lets them linger, directly shifting your risk of deep vein blood clots by over fifty percent.
Location: ABO. Chromosome 9 · 9q34.2 · 133.3 Mb
Estimated prevalence by population
Global 14.7%; European 11.8%; African 18.9%; East Asian 15.4%; South Asian 19.3%; Americas 8.0%; Ashkenazi 18.8%; Finnish 21.3%; Middle Eastern 11.1%; Amish 42.2%.
Estimated GG genotype frequency.
Global 46.4%; European 45.1%; African 49.2%; East Asian 47.7%; South Asian 49.3%; Americas 40.6%; Ashkenazi 49.1%; Finnish 49.7%; Middle Eastern 44.4%; Amish 45.5%.
Estimated GA genotype frequency.
Global 38.9%; European 43.1%; African 31.9%; East Asian 36.9%; South Asian 31.4%; Americas 51.4%; Ashkenazi 32.1%; Finnish 29.1%; Middle Eastern 44.4%; Amish 12.3%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Cardiovascular & Metabolic
Coagulation & Clotting
Venous Thromboembolism. Evidence: 6/10. Source: PMID 23650146. ~1.55x Higher Risk.
Blood Clotting Speed. Evidence: 9/10. Source: PMID 35285134. Higher Clotting.
Diabetes & Glycemic Traits
Type 2 Diabetes. Evidence: 6/10. Source: PMID 30054458. Increased Risk.
Organ Systems
Liver Function & Disease
ALT Liver Enzyme. Evidence: 6/10. Source: PMID 33547301. Elevated Levels.
Showing effects for A/A genotype
Venous Thromboembolism. Evidence: 6/10. Source: PMID 23650146. Typical Risk.
Blood Clotting Speed. Evidence: 9/10. Source: PMID 35285134. Typical Clotting.
Type 2 Diabetes. Evidence: 6/10. Source: PMID 30054458. Typical Risk.
ALT Liver Enzyme. Evidence: 6/10. Source: PMID 33547301. Typical Levels.
Showing effects for G/A genotype
Venous Thromboembolism. Evidence: 6/10. Source: PMID 23650146. Increased Risk.
Blood Clotting Speed. Evidence: 9/10. Source: PMID 35285134. Moderately Higher.
Type 2 Diabetes. Evidence: 6/10. Source: PMID 30054458. Slightly Increased.
ALT Liver Enzyme. Evidence: 6/10. Source: PMID 33547301. Slightly Elevated.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Inheriting two copies of the G allele strongly correlates with having a non-O blood type, which is a well-established driver of elevated cardiovascular risk. This genetic profile leads to slower clearance of von Willebrand factor and coagulation factor VIII, resulting in higher circulating levels of these proteins [1]. Clinical data indicates that this elevation significantly increases the risk of venous thromboembolism, with studies reporting an odds ratio of approximately 1.55 for clot formation [2]. Elevated levels of fibrin D-dimer, a key marker of active blood clotting, are also frequently observed in individuals with this genotype [3]. Additionally, this genetic makeup is associated with higher susceptibility to type 2 diabetes and elevated liver enzymes like alanine aminotransferase. Maintaining a heart-healthy lifestyle and staying active during long periods of immobility can help mitigate these inherited cardiovascular risks.
Elevated risk of deep vein thrombosis; Higher circulating clotting factors; Increased risk of type 2 diabetes.
Sample genotype: AA (Homozygous)
Carrying two copies of the A allele is a hallmark of the O blood group, which is characterized by highly efficient clearance of key coagulation proteins. Because the body breaks down von Willebrand factor and factor VIII more rapidly, circulating levels of these clotting proteins remain low [1]. This natural biological clearance mechanism translates to a significantly lower risk of venous thromboembolism and deep vein thrombosis compared to non-O blood types [2]. Individuals with this genotype also show lower baseline levels of fibrin D-dimer, reflecting a highly stable and typical coagulation profile [3]. Furthermore, this genetic profile is associated with lower risks of type 2 diabetes and typical, healthy levels of the liver enzyme alanine aminotransferase. Overall, this genotype represents a highly favorable cardiovascular profile with built-in genetic protection against unwanted blood clots.
Lower baseline clotting factor levels; Reduced risk of deep vein thrombosis; Typical metabolic and liver enzyme profiles.
Sample genotype: GA (Heterozygous)
Possessing one copy of the G allele indicates a non-O blood group status, which moderately influences systemic blood coagulation dynamics. This heterozygous profile results in intermediate levels of crucial clotting proteins, such as factor VIII and von Willebrand factor, compared to the lower levels seen in blood group O individuals [1]. Consequently, carriers face a moderately elevated risk of venous thromboembolism and deep vein blood clots [2]. Research also links this genetic variation to slightly higher baseline levels of fibrin D-dimer, indicating active coagulation pathways [3]. Beyond cardiovascular traits, the G allele is associated with minor increases in type 2 diabetes risk and slightly elevated alanine aminotransferase liver enzymes. While the risk is lower than that of the G/G genotype, staying hydrated and active during long flights or periods of immobility remains a highly effective preventive strategy.
Moderately higher clotting factor levels; Slightly elevated risk of venous clots; Slightly higher type 2 diabetes risk.
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
Genetic predictors of fibrin D-dimer levels in healthy adults.
Content updated August 2026.
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