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.
OBJECTIVE
To identify the variants in UDP-glucuronosyltransferase 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.


CONCLUSIONS
The genetic epidemiology of GS is variable across ethnic groups and the epistatic interactions among UGT1A1 promoter variants modulate bilirubin glucuronidation.
Farheen
Shabana
S
Human Genetics Unit, Indian Statistical Institute, Kolkata, India.
Sengupta
Sanghamitra
S
Santra
Amal
A
Pal
Suparna
S
Dhali
Gopal Krishna
GK
Chakravorty
Meenakshi
M
Majumder
Partha P
PP
Chowdhury
Abhijit
A
D000328:Adult; D001663:Bilirubin / Q000097:blood; D005260:Female; D005787:Gene Frequency; D005878:Gilbert Disease / Q000097:blood / Q000235:genetics*; D014453:Glucuronosyltransferase / Q000235:genetics*; D006801:Humans; D008297:Male; D011401:Promoter Regions, Genetic; D000099148:UGT1A1 Enzyme
D001663:Bilirubin; D014453:Glucuronosyltransferase; D000099148:UGT1A1 Enzyme