FUT2 rs601338: Understanding Your Secretor Status
The rs601338 variant in the FUT2 gene determines whether an individual is a 'secretor' or 'non-secretor' of blood-group antigens in body fluids. This genetic difference is associated with varying susceptibility to specific viral infections and differences in plasma vitamin B12 levels.
What each genotype means
Secretor status
Individuals with this genotype are considered 'secretors,' meaning they secrete ABO blood group antigens into their body fluids and saliva. This is the most common genotype in many populations and is associated with typical susceptibility to certain viral infections like norovirus.
This is the most common genotype in many global populations.
Secretor status
Carriers of one copy of the A allele are typically secretors, similar to those with the G/G genotype. Research indicates that having at least one G allele allows for the production of the functional FUT2 enzyme required for secreting blood group antigens.
This heterozygous genotype is common across many diverse human populations.
Non-secretor status
Individuals with this genotype are 'non-secretors' because they carry two copies of an enzyme-inactivating nonsense mutation (also referred to as W143X). This status confers resistance to certain infections, such as norovirus, but has been statistically associated with an increased risk for conditions like Crohn's disease, type 1 diabetes, and altered serum vitamin B12 levels. Please discuss any health concerns or specific disease risks with your clinician.
Approximately 20% of individuals in many populations are homozygous for this non-secretor allele.
What is rs601338?
The rs601338 variant is a single nucleotide polymorphism (SNP) located on chromosome 19 within the FUT2 gene. In genetic databases, it is often described by the presence of either a guanine (G) or an adenine (A) nucleotide at a specific position. This variation is well-known in human genetics for its role in defining 'secretor status.' Individuals who possess the functional G allele are typically classified as secretors, meaning they secrete ABO blood-group antigens into bodily fluids like saliva and mucus. Those who are homozygous for the A allele are classified as non-secretors, as they lack the functional enzyme required to secrete these antigens. This simple genetic switch has been the subject of extensive research due to its broad impact on human physiology and interaction with the environment.
The Role of the FUT2 Gene
The FUT2 gene encodes an enzyme called alpha(1,2)-fucosyltransferase. This enzyme is responsible for adding a specific sugar molecule to the H antigen, which is a precursor for ABO blood-group antigens. When the enzyme is active, these antigens are produced and secreted into various body fluids. This process is not just about blood types; it plays a critical role in the mucosal lining of the gut and other tissues. Because these secreted antigens can act as receptors for certain pathogens, the presence or absence of these sugars on mucosal surfaces can significantly alter how the body interacts with viruses and bacteria. Consequently, the FUT2 gene acts as a gatekeeper, influencing the internal environment of the digestive tract and the body's overall immune response to specific external threats.
Research and Associations
Research has consistently linked the rs601338 variant to several health-related traits. One of the most notable associations is with norovirus susceptibility; individuals who are non-secretors (AA genotype) often show resistance to certain strains of norovirus, as the virus struggles to bind to their mucosal cells. Conversely, this same genotype has been associated with an increased risk for other conditions, including type 1 diabetes and inflammatory bowel disease, though the evidence for these associations varies in strength. Additionally, studies have observed that the A allele is associated with higher plasma vitamin B12 levels. While these findings are statistically significant in large population studies, it is important to remember that these are associations, not direct causes. Genetic factors are only one piece of a complex puzzle that includes diet, environment, and overall lifestyle.
Interpreting Your Information
Understanding your rs601338 genotype provides insight into your biological secretor status, but it should not be used to make medical decisions or predict health outcomes. While the variant influences susceptibility to specific infections or metabolic markers like vitamin B12, it does not guarantee that you will or will not develop a specific condition. If you are concerned about your vitamin B12 levels or your risk for specific gastrointestinal issues, it is essential to consult with a healthcare professional. They can provide context based on your full medical history, blood tests, and clinical symptoms. Never use genetic information to self-diagnose or alter your medical care without professional guidance. Genetic data is a tool for education and curiosity, not a substitute for clinical evaluation.
How common is this variant?
The rs601338 variant is common across global populations, with the GMAF (Global Minor Allele Frequency) reported at approximately 0.32.
Frequently asked questions
What does it mean to be a 'secretor'?
Being a secretor means your body produces and releases ABO blood-group antigens into fluids like saliva, tears, and digestive juices. This is determined by the activity of the FUT2 enzyme.
Does being a non-secretor mean I am immune to all viruses?
No. Being a non-secretor (AA genotype) is associated with resistance to specific strains of norovirus, but it does not provide immunity to other viruses or infections.
Can this variant affect my vitamin B12 levels?
Yes, research has shown a statistical association between the rs601338 genotype and plasma vitamin B12 levels. However, your actual B12 status is also heavily influenced by your diet and absorption.
Should I change my diet based on my FUT2 genotype?
There is no standard medical recommendation to change your diet based solely on this SNP. Always discuss any concerns about nutrition or vitamin levels with your doctor or a registered dietitian.
Sources & further reading
Educational information only, last refreshed 10/5/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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