UGT1A1 rs3064744: What Your Genotype Means
The rs3064744 variant is a genetic marker located in the promoter region of the UGT1A1 gene. It is primarily associated with the regulation of bilirubin levels and the metabolism of specific medications, including the chemotherapy drug irinotecan.
What each genotype means
Normal enzyme activity
This genotype corresponds to the UGT1A1*1/*1 status, which is associated with normal enzyme function. Individuals with this profile typically process medications like irinotecan at standard rates, though you should always discuss specific dosing with your clinician or pharmacist.
Carried by approximately 2% of the population based on TA6 allele frequency data.
Intermediate enzyme activity
This genotype corresponds to the UGT1A1*1/*28 status, often classified as an intermediate metabolizer. Research suggests this may lead to slightly reduced enzyme activity compared to those with two copies of the normal allele; please consult your healthcare provider regarding potential medication sensitivities.
This is a common genotype, as the TA7 allele is present in over 60% of the population.
Reduced enzyme activity
This genotype corresponds to the UGT1A1*28/*28 status, which is associated with reduced UGT1A1 enzyme activity and an increased risk of hyperbilirubinemia or toxicity from certain drugs like irinotecan. It is essential to discuss this result with your clinician or pharmacist before starting any medication metabolized by this enzyme.
The TA7 allele is the most common variant form, found in roughly 60% of the population, making this a relatively frequent genotype.
Reduced enzyme activity
This genotype involves the combination of the *28 and *37 alleles, both of which are associated with reduced enzyme function. Individuals with this profile may have a higher risk of drug-related side effects; please review your treatment plan with your medical team.
This genotype is less common than homozygous TA7, reflecting the lower frequency of the TA8 allele in the general population.
Reduced enzyme activity
This genotype corresponds to the UGT1A1*37/*37 status, which is linked to decreased enzyme expression and potential sensitivity to specific drug therapies. Always consult your pharmacist or physician to ensure your medication dosages are appropriate for your genetic profile.
The TA8 allele is found in approximately 35% of the population, making this genotype a notable, though less frequent, occurrence.
Understanding the rs3064744 Variant
The rs3064744 variant is a well-studied genetic marker located within the promoter region of the UGT1A1 gene. Unlike variants that change a single DNA letter, this specific marker involves a variable number of TA repeats. The standard reference sequence typically contains six or seven TA repeats, while variant forms may contain more. Because this region controls how much of the UGT1A1 enzyme is produced, changes in the number of repeats can significantly alter the body's ability to process certain substances. This variant is the primary genetic basis for defining several UGT1A1 star alleles, such as *28, *36, and *37, which are widely used in clinical pharmacogenomics to categorize enzyme activity levels.
The Role of the UGT1A1 Gene
The UGT1A1 gene provides instructions for making an enzyme called UDP-glucuronosyltransferase 1A1. This enzyme is essential for the process of glucuronidation, a chemical reaction that makes substances—such as bilirubin and certain drugs—more water-soluble so they can be easily excreted from the body. Bilirubin is a yellow pigment produced during the normal breakdown of red blood cells. When the UGT1A1 enzyme is less active, bilirubin can build up in the bloodstream, leading to mild jaundice, a condition known as Gilbert syndrome. Beyond bilirubin, this enzyme is responsible for detoxifying various compounds, including the active metabolite of the chemotherapy drug irinotecan. Consequently, the efficiency of this enzyme directly impacts how a patient might respond to specific medical treatments.
Research and Clinical Associations
Research has established a strong link between rs3064744 and the risk of adverse reactions to irinotecan. Patients with reduced UGT1A1 enzyme activity may struggle to clear the drug's active metabolite, increasing the risk of severe side effects like neutropenia and diarrhea. Clinical guidelines, such as those from the Clinical Pharmacogenetics Implementation Consortium (CPIC), use this variant to help clinicians optimize starting doses for patients. Additionally, this variant is a common cause of Gilbert syndrome, a benign condition characterized by intermittent mild hyperbilirubinemia. While the evidence for these associations is robust, it is important to note that individual responses to medication are complex and influenced by multiple genetic and environmental factors. Always consult with your healthcare provider or a pharmacist to interpret how your specific genetic profile might influence your clinical care.
Population Frequency
The frequency of the rs3064744 variant varies significantly across different global populations. For example, the allele associated with reduced enzyme function is relatively common in individuals of African and European descent, where it is a frequent cause of Gilbert syndrome. In contrast, other variants in the UGT1A1 gene, such as those involving different SNPs, may be more prevalent in East Asian populations. Because these frequencies are not uniform, the clinical relevance of testing for this variant can depend heavily on an individual's ancestry. Large-scale genomic databases continue to refine these frequency estimates, providing a clearer picture of how this genetic diversity is distributed worldwide.
What You Can Do With This Information
Knowing your genotype for rs3064744 can be a valuable piece of information for your medical team, particularly if you are prescribed medications metabolized by the UGT1A1 enzyme. If you have received genetic testing results, you should share them with your doctor or a clinical pharmacist. They can help determine if your specific genotype warrants a dose adjustment or closer monitoring for potential side effects. It is critical to remember that this information is not a diagnosis and should never be used to make independent medical decisions. Genetic markers are only one part of a larger clinical picture that includes your medical history, current health status, and other medications you may be taking. Always rely on professional medical guidance when interpreting genetic data.
How common is this variant?
The frequency of the rs3064744 variant is variable; it is common in many populations, with specific allele frequencies differing significantly between African, European, and Asian ancestries.
Frequently asked questions
Is rs3064744 the same as Gilbert syndrome?
The rs3064744 variant is a common genetic cause of Gilbert syndrome. However, having the variant does not guarantee you will have the condition, and other factors can also influence bilirubin levels.
Does this variant affect all medications?
No, this variant specifically affects the metabolism of drugs processed by the UGT1A1 enzyme, such as irinotecan. It does not impact the metabolism of most other common medications.
Should I get tested for this variant?
Genetic testing for UGT1A1 is typically ordered by a physician if you are scheduled to receive a medication known to be affected by this gene. You should discuss the necessity of testing with your healthcare provider.
Can I change my UGT1A1 genotype?
No, your genotype is inherited and cannot be changed. However, knowing your genotype allows your doctor to adjust your medical treatment plan to ensure safety and efficacy.
Sources & further reading
Educational information only, last refreshed 10/7/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This variant is associated with hyperbilirubinaemia (Gilbert's syndrome) and is used to guide irinotecan dosage.
Missense variant corresponding to the functional UGT1A1*27 allele associated with reduced glucuronidation and elevated irinotecan toxicity risk.
Variant allele in UGT1A1 (defining UGT1A1*60 in the promoter region) associated with altered glucuronidation and elevated risk of irinotecan-induced neutropenia and hyperbilirubinemia.
The TT genotype is associated with significantly increased serum bilirubin concentrations in pediatric populations.
Missense alteration associated with reduced glucuronidation capacity and increased susceptibility to irinotecan toxicity and hyperbilirubinemia.
This variant in the UGT1A gene cluster is associated with serum total bilirubin levels and susceptibility to Gilbert syndrome.