Gilbert's syndrome causes mild, unconjugated hyperbilirubinemia and is present 
in approximately 10% of the Caucasian population. The basis of the disorder is a 
70% reduction in bilirubin glucuronidation catalyzed by the 
UDP-glucuronosyltransferase 1A1 (UGT1A1), which, in Caucasians, is the result of 
a homozygous TA insertion into the promoter region of the UGT1A1 gene 
(UGT1A1*28). Homozygous carriers of UGT1A1*28 as well as those with additional 
UGT1A variants can suffer from severe irinotecan toxicity or jaundice during 
treatment with the protease inhibitor atazanavir. UGT1A1*28 genotyping 
identifies patients at risk for drug toxicity and can increase drug safety by 
dose individualization. Rapid and facile UGT1A1*28 genotyping is therefore of 
great clinical importance. Two hundred ninety-one patients with suspected 
Gilbert's syndrome were genotyped using the TaqMan 5'nuclease assay with minor 
groove binder-non fluorescent quench probes; results were confirmed by direct 
sequencing. Ninety-six patients (33%) were homozygous for UGT1A1*28, which was 
verified by direct sequencing of a different PCR product showing 100% 
concordance with the TaqMan PCR results. We describe a novel UGT1A1*28 
genotyping method that employs allelic discrimination by TaqMan PCR. This assay 
provides a rapid, high-throughput, and cost-effective method for Gilbert's 
syndrome genotyping, which is of value for pretreatment screening of potential 
irinotecan toxicity. The method utilizes a technological platform that is widely 
used in clinical practice and could therefore be easily adapted for routine 
clinical applications.