Uridine Diphosphate (UDP) Glucuronosyltransferase 1A1 TA Repeat Genotype, UGT1A1, Varies

Casandra

Casandra Test Code MC70730Version 1 (DRAFT)

Performing Lab

Lab Mayo Clinic LabLab Test ID U1A1QCPT Code 81350

Uridine Diphosphate (UDP) Glucuronosyltransferase 1A1 TA Repeat Genotype, UGT1A1, Varies

Clinical Use

Use

This pharmacogenomic test interrogates the thymine‑adenine (TA) repeat in the TATA‑box promoter region of UGT1A1 and evaluates the UGT1A1*6 (c.211G>A) allele. Variability in TA repeat counts (TA5–TA8) affects UGT1A1 enzymatic activity. Individuals with TA7, TA8, or compound heterozygous configurations exhibit reduced activity associated with Gilbert syndrome or increased risk of adverse drug reactions, especially to irinotecan and other UGT1A1‑metabolized drugs. The test is not informative for Crigler‑Najjar syndrome. Reduced UGT1A1 expression due to TA repeat variation and UGT1A1*6 variant elevates risk of adverse drug outcomes. Samples from individuals with recent transfusions or transplants may yield inaccurate results unless pre‑transplant DNA is used. Male liver or kidney dysfunction also independently affects drug response risk.

Special Instructions

New York clients require documented informed consent (forms T576 or T826). Order must include appropriate request form if not electronic (e.g., Therapeutics Test Request T831 or Oncology Test Request T729). Pre‑transplant DNA specimen is recommended for hematopoietic stem cell transplant recipients. This test uses a tagging SNP strategy and cannot distinguish TA7 vs TA8—they are both reported as TA7.

Limitations

The assay targets only TA5–TA8 repeats and UGT1A1*6; rare or additional variants outside these are not detected. Sequencing is available for full gene coverage. The tagging SNP method cannot distinguish between TA7 and TA8. Donor DNA from transfusions or transplant recipients may impact genotyping; reversion may occur 6 weeks post transfusion. Results from liver transplant recipients may not reflect the patient's genotype. Organ dysfunction may independently affect drug toxicity risk.

Test Details

New York Approved