What you carry at this position in your DNA and what research says about it.
Vel Blood Group Antigen: 10/10 evidence, 13 publications.
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Sample genotype (not yours): A/A
Weaker Vel Antigen Expression and Lower Hemoglobin
Weaker expression of the Vel blood group antigen on red blood cells is associated with this genetic profile. It also correlates with slightly lower hemoglobin levels and red blood cell counts.
What this genotype means: Weaker Vel antigen expression; Slightly lower hemoglobin levels; Slightly higher red cell distribution width.
Sample genotype (not yours): A/G
Typical Vel Antigen Expression and Blood Cell Counts
Typical expression of the Vel blood group antigen occurs with this heterozygous profile. It represents an intermediate, healthy balance of red blood cell traits.
What this genotype means: Typical Vel antigen expression; Average hemoglobin levels; Typical red blood cell counts.
Sample genotype (not yours): G/G
Stronger Vel Antigen Expression and Higher Hemoglobin
Stronger expression of the Vel blood group antigen on red blood cells characterizes this genetic profile. It also correlates with slightly higher hemoglobin levels and red blood cell counts.
What this genotype means: Stronger Vel antigen expression; Slightly higher hemoglobin levels; Slightly higher red blood cell count.
Gene function and biological role
Gene Function: The SMIM1 gene encodes small integral membrane protein 1, which is the essential carrier of the Vel blood group antigen on red blood cells [1]. Discovered over sixty years ago, the Vel antigen is present in more than 99.9% of the global population [1]. Individuals who completely lack SMIM1 expression due to rare homozygous deletions are classified as Vel-negative [1]. These rare individuals can develop severe transfusion reactions if they receive Vel-positive blood [1]. Beyond blood typing, SMIM1 plays a critical role in regulating red blood cell formation and overall erythrocyte development [1].
Variant Impact: The rs1175550 variant is a common genetic change in the SMIM1 gene that directly regulates how much Vel antigen is produced on red blood cells [1]. Having the G allele increases SMIM1 gene expression, resulting in stronger Vel antigen levels on the cell surface [1]. This genetic variation also influences broader blood characteristics, including hemoglobin levels and red blood cell counts [1] [2]. Conversely, the A allele is linked to weaker Vel antigen expression and lower baseline SMIM1 transcript levels [1]. These differences help explain natural, healthy variations in blood cell traits across populations [2].
Key Insight: The Vel blood group antigen was a mystery for over 60 years until researchers discovered it is carried by the SMIM1 protein, which is regulated by this very variant.
Location: SMIM1. Chromosome 1 · 1p36.32 · 3.8 Mb
Estimated prevalence by population
Global 50.5%; European 58.7%; African 22.7%; East Asian 99.5%; South Asian 68.7%; Americas 66.8%; Ashkenazi 52.4%; Finnish 48.9%; Middle Eastern 50.5%; Amish 69.6%.
Estimated AA genotype frequency.
Global 38.1%; European 35.8%; African 49.9%; East Asian 0.5%; South Asian 28.4%; Americas 29.9%; Ashkenazi 40.0%; Finnish 42.1%; Middle Eastern 41.1%; Amish 27.7%.
Estimated AG genotype frequency.
Global 11.3%; European 5.5%; African 27.4%; East Asian < 0.1%; South Asian 2.9%; Americas 3.3%; Ashkenazi 7.6%; Finnish 9.1%; Middle Eastern 8.4%; Amish 2.8%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Vel Antigen Expression. Evidence: 3/10. Source: PMID 23563608. Weaker Expression.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 32888494. Slightly Lower.
Red Blood Cell Count. Evidence: 10/10. Source: PMID 32888494. Slightly Lower.
Reticulocyte Count. Evidence: 9/10. Source: PMID 32888494. Slightly Lower.
Red Cell Distribution Width. Evidence: 10/10. Source: PMID 32888494. Slightly Higher.
Diabetes & Glycemic Traits
HbA1c. Evidence: 9/10. Source: PMID 34594039. Slightly Higher.
Showing effects for A/G genotype
Vel Antigen Expression. Evidence: 3/10. Source: PMID 23563608. Typical Expression.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 32888494. Typical.
Red Blood Cell Count. Evidence: 10/10. Source: PMID 32888494. Typical.
Reticulocyte Count. Evidence: 9/10. Source: PMID 32888494. Typical.
Red Cell Distribution Width. Evidence: 10/10. Source: PMID 32888494. Typical.
HbA1c. Evidence: 9/10. Source: PMID 34594039. Typical.
Showing effects for G/G genotype
Vel Antigen Expression. Evidence: 3/10. Source: PMID 23563608. Stronger Expression.
Hemoglobin Levels. Evidence: 10/10. Source: PMID 32888494. Slightly Higher.
Red Blood Cell Count. Evidence: 10/10. Source: PMID 32888494. Slightly Higher.
Reticulocyte Count. Evidence: 9/10. Source: PMID 32888494. Slightly Higher.
Red Cell Distribution Width. Evidence: 10/10. Source: PMID 32888494. Slightly Lower.
HbA1c. Evidence: 9/10. Source: PMID 34594039. Slightly Lower.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Two copies of the major A allele are linked to lower SMIM1 gene expression [1]. This leads to weaker expression of the Vel antigen on red blood cells, though they remain Vel-positive [1]. Standard blood typing may occasionally show weaker reactivity, but it does not mean the individual is Vel-negative [1]. This genotype also correlates with slightly lower hemoglobin levels and red blood cell counts [2]. Additionally, it is associated with a slightly higher red cell distribution width [2]. These variations are physiological and do not indicate anemia or any other blood disorder [2].
Weaker Vel antigen expression; Slightly lower hemoglobin levels; Slightly higher red cell distribution width.
Sample genotype: AG (Heterozygous)
One copy of each allele results in intermediate SMIM1 gene expression and typical Vel antigen levels [1]. Red blood cells display standard levels of the Vel antigen, ensuring normal compatibility in blood typing [1]. Hemoglobin levels, red blood cell counts, and reticulocyte counts generally fall near the population average [2]. This heterozygous state provides a balanced physiological profile without any clinical concerns [2]. It is the most common genotype in many global populations, reflecting a standard baseline [2]. No negative health outcomes or hematological risks are associated with this genotype [2].
Typical Vel antigen expression; Average hemoglobin levels; Typical red blood cell counts.
Sample genotype: GG (Homozygous)
Two copies of the high-expressing G allele enhance SMIM1 gene activity [1]. This results in robust expression of the Vel antigen on the surface of red blood cells, making standard blood typing highly reliable [1]. Research shows this genotype is also associated with slightly higher hemoglobin levels and red blood cell counts [2]. Additionally, it correlates with an increased reticulocyte count, which represents newly formed red blood cells [2]. These physiological variations are entirely healthy and fall within normal clinical ranges [2]. There is no associated risk of blood disorders or other adverse health conditions with this genotype [2].
Stronger Vel antigen expression; Slightly higher hemoglobin levels; Slightly higher red blood cell count.
Variants with shared genetic architecture
rs11085824 · GCDH Gene · Chr 19 · Red Blood Cell Traits
rs1256061 · ESR2 Gene · Chr 14 · Blood Oxygen Capacity
rs1434282 · LINC01221 Gene · Chr 1 · Blood Cell Characteristics
SMIM1 underlies the Vel blood group and influences red blood cell traits.
The Polygenic and Monogenic Basis of Blood Traits and Diseases.
Content updated August 2026.
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