Combined effect of regulatory polymorphisms on transcription of UGT1A1 as a cause of Gilbert syndrome.
BACKGROUND
Gilbert syndrome is caused by defects in bilirubin UDP-glucuronosyltransferase (UGT1A1). The most common variation believed to be involved is A(TA)7TAA. Although several polymorphisms have been found to link with A(TA)7TAA, the combined effect of regulatory polymorphisms in the development of Gilbert syndrome remains unclear.


METHODS
In an analysis of 15 patients and 60 normal subjects, we detected 14 polymorphisms and nine haplotypes in the regulatory region. We classified the 4-kbp regulatory region of the patients into: the TATA box including A(TA)7TAA; a phenobarbital responsive enhancer module including c.-3275T>G; and a region including other ten linked polymorphisms. The effect on transcription of these polymorphisms was studied.


RESULTS
All haplotypes with A(TA)7TAA had c.-3275T>G and additional polymorphisms. In an in-vitro expression study of the 4-kbp regulatory region, A(TA)7TAA alone did not significantly reduce transcription. In contrast, c.-3275T>G reduced transcription to 69% of that of wild type, and the linked polymorphisms reduced transcription to 88% of wild type. Transcription of the typical regulatory region of the patients was 56% of wild type. Co-expression of constitutive androstane receptor (CAR) increased the transcription of wild type by a factor of 4.3. Each polymorphism by itself did not reduce transcription to the level of the patients, however, even in the presence of CAR.


CONCLUSIONS
These results imply that co-operation of A(TA)7TAA, c.-3275T>G and the linked polymorphisms is necessary in causing Gilbert syndrome.
Matsui
Katsuyuki
K
Department of Pediatrics, Shiga University of Medical Science, Tsukinowa, Seta, Otsu, Shiga 520-2192, Japan.
Maruo
Yoshihiro
Y
Sato
Hiroshi
H
Takeuchi
Yoshihiro
Y
D044466:Asian People / Q000235:genetics; D016022:Case-Control Studies; D000090702:Constitutive Androstane Receptor; D005878:Gilbert Disease / Q000235:genetics* / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000235:genetics*; D006239:Haplotypes / Q000235:genetics; D006801:Humans; D007564:Japan; D011110:Polymorphism, Genetic / Q000235:genetics*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D014158:Transcription, Genetic; D044465:White People / Q000235:genetics; D000099148:UGT1A1 Enzyme
D000090702:Constitutive Androstane Receptor; D014453:Glucuronosyltransferase; D018160:Receptors, Cytoplasmic and Nuclear; D000099148:UGT1A1 Enzyme