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World J Gastroenterol. Apr 14, 2006; 12(14): 2269-2275
Published online Apr 14, 2006. doi: 10.3748/wjg.v12.i14.2269
Gilbert’s syndrome: High frequency of the (TA)7 TAA allele in India and its interaction with a novel CAT insertion in promoter of the gene for bilirubin UDP-glucuronosyltransferase 1 gene
Shabana Farheen, Sanghamitra Sengupta, Amal Santra, Suparna Pal, Gopal Krishna Dhali, Meenakshi Chakravorty, Partha P Majumder, Abhijit Chowdhury
Shabana Farheen, Sanghamitra Sengupta, Partha P Majumder, Human Genetics Unit, Indian Statistical Institute, Kolkata, India
Amal Santra, Suparna Pal, Gopal Krishna Dhali, Abhijit Chowdhury, Department of Gastroenterology, Institute of Postgraduate Medical Education & Research, Kolkata, India
Meenakshi Chakravorty, Human Genetics & Genomics Division, Indian Institute of Chemical Biology, Kolkata, India
Supported by grants from the Department of Biotechnology, Government of India (to PPM) and the Department of Science & Technology, Government of West Bengal (to AC)
Correspondence to: Abhijit Chowdhury, MD, Department of Gastroenterology, Institute of Postgraduate Medical Education and Research, Kolkata 700020, India. achowdhury@apexmail.com
Telephone: +91-332553209
Received: June 4, 2005
Revised: July 1, 2005
Accepted: October 10, 2005
Published online: April 14, 2006
Abstract

AIM: To identify the variants in UDP-glucuronosyltransfe-rase 1 (UGT1A1) gene in Gilbert’s syndrome (GS) and to estimate the association between homozygosity for TA insertion and GS in India, as well as the frequency of TA insertion and its impact among normal controls in India.

METHODS: Ninety-five GS cases and 95 normal controls were selected. Liver function and other tests were done. The promoter and all 5 exons of UGT1A1 gene were resequenced. Functional assessment of a novel trinucleotide insertion was done by in silico analysis and by estimating UGT1A1 promoter activity carried out by luciferase reporter assay of appropriate constructs in Hep G2 cell line.

RESULTS: Among the GS patients, 80% were homozygous for the TA insertion, which was several-fold higher than reports from other ethnic groups. The mean UCB level was elevated among individuals with only one copy of this insertion, which was not significantly different from those with two copies. Many new DNA variants in UGT1A1 gene were discovered, including a trinucleotide (CAT) insertion in the promoter found in a subset (10%) of GS patients, but not among normal controls. In-silico analysis showed marked changes in the DNA-folding of the promoter and functional analysis showed a 20-fold reduction in transcription efficiency of UGT1A1 gene resulting from this insertion, thereby significantly elevating the UCB level.

CONCLUSION: The genetic epidemiology of GS is variable across ethnic groups and the epistatic interactions among UGT1A1 promoter variants modulate bilirubin glucuronidation.

Keywords: Unconjugated hyperbilirubinemia; UGT1A1 gene; DNA resequencing; Luciferase reporter assay