What you carry at this position in your DNA and what research says about it.
Stomach Flu Resistance: 8/10 evidence, 31 publications.
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Sample genotype (not yours): G/G
Typical Stomach Flu Susceptibility
Secretor status means expressing blood group antigens in bodily fluids, which supports gut microbiome diversity but leaves you susceptible to common norovirus strains.
What this genotype means: Susceptible to common norovirus strains; Supports typical gut microbiome diversity; Typical baseline risk for inflammatory bowel disease.
Sample genotype (not yours): A/A
Stomach Flu Resistance but Higher Autoimmune Risk
Non-secretor status grants near-complete immunity to common norovirus strains, though it is linked to lower gut microbiome diversity and a higher risk of inflammatory conditions.
What this genotype means: Highly resistant to common norovirus strains; Lower levels of beneficial gut Bifidobacteria; Increased risk of Crohn's disease and gallstones.
Sample genotype (not yours): G/A
Secretor status is maintained with a single functional copy of the gene, keeping you susceptible to common norovirus strains but supporting typical gut microbiome diversity.
Gene function and biological role
Gene Function: The FUT2 gene encodes fucosyltransferase 2, an enzyme responsible for secreting ABO blood group antigens into bodily fluids like saliva and mucus [1]. These soluble antigens act as attachment sites and food for beneficial gut bacteria [2]. People who produce these antigens are known as secretors, while those who do not are non-secretors [1]. Secretor status plays a major role in gut microbiome composition, immune defense, and susceptibility to various pathogens [2].
Variant Impact: The rs601338 variant is a nonsense mutation in the FUT2 gene that introduces a premature stop codon, resulting in a completely nonfunctional enzyme [1]. Carrying two copies of the inactive A allele prevents the secretion of blood group antigens onto mucosal surfaces and into bodily fluids [1]. This lack of surface antigens prevents certain pathogens, such as norovirus, from binding to and infecting intestinal cells [2]. However, it also alters the gut environment, reducing the abundance of beneficial bacteria like Bifidobacteria [3].
Read on the Secretor Status page
Key Insight: Being a non-secretor provides near-complete genetic immunity to the most common strains of norovirus, the leading cause of stomach flu.
Location: FUT2. Chromosome 19 · 19q13.33 · 48.7 Mb
Origin Story: The non-secretor variant has risen to high frequencies in European and African populations likely due to historical evolutionary pressure, where resisting devastating waterborne viral outbreaks provided a survival advantage despite the trade-offs in gut health.
Estimated prevalence by population
Global 32.2%; European 27.3%; African 25.1%; East Asian 99.2%; South Asian 49.6%; Americas 39.9%; Ashkenazi 30.9%; Finnish 40.0%; Middle Eastern 19.6%; Amish 42.2%.
Estimated GG genotype frequency.
Global 47.3%; European 49.9%; African 50.0%; East Asian 0.8%; South Asian 41.6%; Americas 46.5%; Ashkenazi 49.4%; Finnish 46.5%; Middle Eastern 49.3%; Amish 45.5%.
Estimated GA genotype frequency.
Global 20.4%; European 22.8%; African 24.9%; East Asian < 0.1%; South Asian 8.7%; Americas 13.6%; Ashkenazi 19.7%; Finnish 13.5%; Middle Eastern 31.1%; Amish 12.3%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Immunity & Inflammation
Infection Susceptibility & Resistance
Norovirus Resistance. Evidence: 3/10. Source: PMID 12692541. Typical.
Chronic Inflammatory Diseases
Crohn's Disease. Evidence: 4/10. Source: PMID 23075394. Typical.
Organ Systems
Digestive & Gut Disorders
Gut Microbiome. Evidence: 4/10. Source: PMID 30376117. Typical.
Gallstones. Evidence: 8/10. Source: PMID 30504769. Typical.
Nutrition & Metabolism
Vitamin & Mineral Metabolism
Vitamin B12 Levels. Evidence: 8/10. Source: PMID 18776911. Typical.
Showing effects for A/A genotype
Norovirus Resistance. Evidence: 3/10. Source: PMID 12692541. Highly Resistant.
Crohn's Disease. Evidence: 4/10. Source: PMID 23075394. Increased Risk.
Gut Microbiome. Evidence: 4/10. Source: PMID 30376117. Reduced.
Gallstones. Evidence: 8/10. Source: PMID 30504769. ~9% Increased Risk.
Vitamin B12 Levels. Evidence: 8/10. Source: PMID 18776911. ~16-18% Higher.
Showing effects for G/A genotype
Gallstones. Evidence: 8/10. Source: PMID 30504769. Slightly Increased.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Secretor status is determined by the presence of functional G alleles, which are highly common globally [1]. Your body actively secretes ABO blood group antigens into your saliva, digestive tract, and other mucosal secretions [1]. These sugars serve as crucial binding sites and nourishment for beneficial gut microbes, particularly Bifidobacteria [2]. While this supports a healthy, diverse microbiome, these same surface sugars are unfortunately exploited by noroviruses [3]. The virus uses them as anchors to attach to and infect your intestinal cells, making you susceptible to the classic stomach flu [3]. On the positive side, you have a typical baseline risk for inflammatory bowel diseases and normal vitamin B12 levels [4].
Susceptible to common norovirus strains; Supports typical gut microbiome diversity; Typical baseline risk for inflammatory bowel disease.
Sample genotype: AA (Homozygous)
Homozygosity for the inactive A allele makes you a non-secretor, meaning you do not express blood group antigens in your bodily fluids or gut lining [1]. This lack of surface sugars means that common norovirus strains cannot bind to your intestinal cells, granting you strong genetic resistance to the stomach flu [2]. However, the absence of these sugars also means beneficial gut bacteria, such as Bifidobacteria, have fewer attachment sites and nutrients, often leading to lower microbiome diversity [3]. This altered gut environment is associated with an increased risk of inflammatory bowel diseases like Crohn's disease [4]. Additionally, non-secretors tend to have significantly higher circulating vitamin B12 levels [5]. You also have a slightly higher risk of developing gallstones [6].
Highly resistant to common norovirus strains; Lower levels of beneficial gut Bifidobacteria; Increased risk of Crohn's disease and gallstones; Higher circulating vitamin B12 levels.
Sample genotype: GA (Heterozygous)
Heterozygous G/A individuals possess one functional G allele and one inactive A allele, which still allows the body to produce functional fucosyltransferase 2 enzyme [1]. As a secretor, you express blood group antigens in your saliva and gastrointestinal secretions [1]. This provides the necessary environment to support beneficial gut bacteria like Bifidobacteria [2]. However, because these antigens are present on your intestinal lining, you remain susceptible to norovirus infections, which use these sugars to gain entry into your cells [3]. Your risk profile for inflammatory conditions like Crohn's disease and your vitamin B12 levels remain at the typical population baseline [4]. Overall, your health outcomes and gut characteristics are highly similar to those with the G/G genotype.
Variants with shared genetic architecture
rs516246 · FUT2 Gene · Chr 19 · Gut Health and Immunity
rs602662 · FUT2 Gene · Chr 19 · Vitamin B12 and Gut Health
rs1047781 · FUT2 Gene · Chr 19 · Norovirus and Gut Health
Human susceptibility and resistance to Norwalk virus infection.
FUT2 Genetic Variants and Reported Respiratory and Gastrointestinal Illnesses During Infancy.
Common variants of FUT2 are associated with plasma vitamin B12 levels.
Content updated August 2026.
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