(TA)8 allele in the UGT1A1 gene promoter of a Caucasian with Gilbert's syndrome

Abstract

BACKGROUND AND OBJECTIVE: Gilbert's syndrome, a chronic non-hemolytic unconjugated hyperbilirubinemia, is caused by a reduction in the activity of hepatic bilirubin UDP-glucuronosyltransferase (UGT1A1). This reduction has been shown to be due to a polymorphism in the promoter region of the UGT1A1 gene. The presence of seven thymine adenine (TA) repeats reduces the efficiency of transcription of the UGT1A1 gene. To elucidate the genetic background of a patient affected by Gilbert's syndrome, we collected blood samples from family members for the analysis of the A(TA)nTAA motif in the promoter region of the UGT1A1 gene. DESIGN AND METHODS: Analysis of the A(TA)nTAA motif in the promoter region of the UGT1A1 gene was performed by PCR. Estimation of UGT1A1 promoter containing the variable (TA) repeats was performed by using a luciferase reporter system. RESULTS: Three different genotypes were identified due to the presence of (TA)6, (TA)7 and (TA)8 repeats. The production of luciferase decreases in inverse relation to the number of repeats. INTERPRETATION AND CONCLUSIONS: The (TA)7 polymorphism, associated with Gilbert syndrome, is the only allele found up to now in white populations, while two other variants (TA)5 and (TA)8 have been identified in black populations. We describe here the first case of a subject affected by Gilbert's syndrome who is heterozygous for the (TA)8 allele in the promoter region of the UGT1A1 gene. This polymorphism, as well as the (TA)7 one, is associated with an increased level of bilirubin and a significant reduction of transcription activity of the UGT1A1 gene.