Use of Fully Denaturing HPLC for UGT1A1 Genotyping in Gilbert Syndrome (Technical Briefs‪)‬

Gilbert syndrome is an inborn error of bilirubin conjugation caused by mutations in the conjugating enzyme uridine diphosphate glucuronyltransferase (UGT1A1) (1). UGT1A1 activity is moderately reduced in Gilbert syndrome, causing low-grade nonhemolytic unconjugated hyperbilirubinemia without other biochemical or clinical features of hepatic or hematologic pathology. Bilirubin concentrations typically fluctuate over time and tend to be increased in response to metabolic stress such as intercurrent illness and fasting (2). The clinical importance of Gilbert syndrome derives from its high population prevalence. The causative mutation in Caucasians is almost exclusively a dinucleotide insertion in the TATA box of the UGT1A1 promoter. The most common UGT1A1 promoter contains the sequence [(TA).sub.6],TAA; insertion of an extra TA reduces expression of the UGT1A1 gene to 20%-30% of reference values (3). The frequency of the (TA),TAA allele (also known as UGT1A1*28) in the Caucasian population is -0.35; therefore, nearly all Caucasians with Gilbert syndrome are homozygous for this allele (4). UGT1A1*28 is less frequent in Asians. A significant proportion of Asians with Gilbert syndrome have UGT1A1*28 as one mutant allele, but other substitutions that diminish UGT1A1 activity are more common, including p.G71R and p.P229Q (5). Indeed, given the frequency of UGT1A1*28, 10%-15% of Caucasians are homozygous for this allele; however, the prevalence of clinical Gilbert syndrome has been estimated at 5%. The difference between these 2 values may reflect an ascertainment bias, relatively low penetrance of UGT1A1 *28 homozygosity, or a combination of both (1, 3 )