What you carry at this position in your DNA and what research says about it.
Drug and Bilirubin Clearance: 9/10 evidence, 18 publications.
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Sample genotype (not yours): G/G
Typical Drug Metabolism and Standard Bilirubin Levels
Standard enzyme activity allows for normal clearance of medications and metabolic waste. The risk of experiencing severe side effects from specific therapies remains at the typical baseline.
What this genotype means: Standard chemotherapy side effect risk; Typical baseline bilirubin levels.
Sample genotype (not yours): A/A
Significantly Reduced Drug Clearance and Elevated Bilirubin
Highly reduced enzyme activity slows the clearance of certain medications and of bilirubin, which is associated with a higher risk of severe side effects from some chemotherapy drugs.
What this genotype means: High risk of severe chemotherapy toxicity; Elevated baseline bilirubin levels; Slightly lower total cholesterol levels.
Sample genotype (not yours): G/A
Moderately Reduced Drug Clearance and Increased Side Effect Risk
Reduced enzyme activity slows the clearance of certain medications, moderately increasing the risk of treatment-related toxicities.
What this genotype means: Moderately higher risk of chemotherapy side effects; Slightly reduced clearance of certain antipsychotics.
Gene function and biological role
Gene Function: The UGT1A10 gene belongs to a critical cluster of enzymes responsible for glucuronidation, a primary detoxification pathway in the body. This process attaches glucuronic acid to lipophilic molecules, making them water-soluble so they can be safely excreted through bile or urine. The enzyme is highly active in the gastrointestinal tract and liver, where it processes both foreign substances and internal waste. Along with its sister gene UGT1A1, it plays a major role in clearing cellular breakdown products and clinical medications. Variations across this gene region can significantly alter overall metabolic capacity and drug tolerance.
Variant Impact: The rs10929302 variant is an intronic genetic change located within the UGT1A gene cluster on chromosome 2. This variant is also known as UGT1A1*93 and is in strong linkage disequilibrium with other functional promoter variants like UGT1A1*28. The presence of the A allele is associated with reduced transcriptional activity of the glucuronidation enzymes. This reduction in enzyme expression slows down the clearance of both endogenous waste products and specific therapeutic drugs. Consequently, it serves as a key clinical marker for predicting drug toxicities and baseline liver enzyme function.
Key Insight: The A allele of this variant reduces the liver's ability to clear certain chemotherapy drugs, significantly increasing the risk of severe side effects like neutropenia.
Location: UGT1A1. Chromosome 2 · 2q37.1 · 233.8 Mb
Estimated prevalence by population
Global 49.2%; European 50.5%; African 48.7%; East Asian 77.0%; South Asian 37.7%; Americas 49.6%; Ashkenazi 43.6%; Finnish 36.6%; Middle Eastern 49.3%; Amish 36.6%.
Estimated GG genotype frequency.
Global 41.6%; European 41.1%; African 42.2%; East Asian 21.5%; South Asian 47.4%; Americas 41.7%; Ashkenazi 44.9%; Finnish 47.8%; Middle Eastern 41.8%; Amish 47.8%.
Estimated GA genotype frequency.
Global 9.2%; European 8.4%; African 9.1%; East Asian 1.5%; South Asian 14.9%; Americas 8.8%; Ashkenazi 11.5%; Finnish 15.6%; Middle Eastern 8.9%; Amish 15.6%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Pharmacogenomics
Chemotherapy Response
Irinotecan Toxicity. Evidence: 8/10. Source: PMID 15007088. Typical Risk.
Antidepressant & Psychiatric Drug Response
Risperidone Response. Evidence: 5/10. Source: PMID 29955115. Typical Response.
Drug Metabolism Enzyme Activity
Fesoterodine Metabolism. Evidence: 5/10. Source: PMID 39338398. Typical Metabolism.
Organ Systems
Liver Function & Disease
Bilirubin Levels. Evidence: 9/10. Source: PMID 22085899. Typical Levels.
Cardiovascular & Metabolic
Lipids & Cholesterol
Total Cholesterol. Evidence: 8/10. Source: PMID 33462484. Slightly Higher.
Neurology & Mental Health
Sleep & Circadian Rhythm
Insomnia. Evidence: 8/10. Source: PMID 34343768. Typical Risk.
Showing effects for A/A genotype
Irinotecan Toxicity. Evidence: 8/10. Source: PMID 15007088. High Risk.
Fesoterodine Metabolism. Evidence: 5/10. Source: PMID 39338398. Faster Metabolism.
Bilirubin Levels. Evidence: 9/10. Source: PMID 22085899. Elevated Levels.
Total Cholesterol. Evidence: 8/10. Source: PMID 33462484. Slightly Lower.
Insomnia. Evidence: 8/10. Source: PMID 34343768. Altered Risk.
Showing effects for G/A genotype
Irinotecan Toxicity. Evidence: 8/10. Source: PMID 15007088. Increased Risk.
Risperidone Response. Evidence: 5/10. Source: PMID 29955115. Elevated Prolactin.
Total Cholesterol. Evidence: 8/10. Source: PMID 33462484. Typical Levels.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Normal glucuronidation activity ensures that the body efficiently processes and excretes various substances, including therapeutic drugs and cellular byproducts. Clinical studies demonstrate that carrying two copies of the G allele is associated with a standard, baseline risk of toxicity when undergoing chemotherapy with irinotecan. Bilirubin levels typically remain within the normal reference range, reflecting efficient liver clearance. While total cholesterol levels may trend slightly higher compared to carriers of the variant allele, overall metabolic function is well-balanced.
Standard chemotherapy side effect risk; Typical baseline bilirubin levels.
Sample genotype: AA (Homozygous)
Having two copies of the A allele leads to a pronounced reduction in glucuronidation enzyme expression and activity. This metabolic slowdown significantly increases the risk of severe, dose-limiting toxicities, such as grade 4 neutropenia and severe diarrhea, when treated with the chemotherapy drug irinotecan. The reduced clearance also causes unconjugated bilirubin to accumulate in the blood, a benign condition often referred to as Gilbert's syndrome. Conversely, this genotype is associated with slightly lower total cholesterol levels, representing a minor metabolic trade-off.
High risk of severe chemotherapy toxicity; Elevated baseline bilirubin levels; Slightly lower total cholesterol levels.
Sample genotype: GA (Heterozygous)
Carrying one copy of the A allele moderately reduces the efficiency of the glucuronidation pathway, which can slow the breakdown of certain drugs. Clinical evidence indicates that this intermediate metabolism state increases the severity of neutropenia, a drop in white blood cells, during irinotecan chemotherapy. Additionally, there is a moderately elevated risk of experiencing elevated prolactin levels if treated with the antipsychotic medication risperidone. Bilirubin levels generally remain close to the typical range, though clearance is slightly less efficient than in the major genotype.
Moderately higher risk of chemotherapy side effects; Slightly reduced clearance of certain antipsychotics.
Variants with shared genetic architecture
rs6742078 · UGT1A1 Gene · Chr 2 · Gallstone Risk
rs887829 · UGT1A1 Gene · Chr 2 · Bilirubin and Heart Health
rs4148323 · UGT1A1 Gene · Chr 2 · Bilirubin and Drug Metabolism
Content updated September 2026.
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