Objective: The aim of this study was to define the underlying molecular genetic basis of reduced expression in UGT1A1, leading to increased serum total bilirubin concentration in Omani sickle cell anemia patients.

Background: UDP-glucuronosyltranferase 1A1 (UGT1A1) is the key enzyme for bilirubin conjugation. Several polymorphisms in the UGT1A1 gene have been reported to be associated with decreased enzyme activity. Sickle cell disease(SCD) is a congenital hemolytic anemia with increased red cell destruction and an additional reduction in the UGT1A1 enzyme activity will lead to hyperbilirubinemia and its complications.

Methods: The study enrolled a total of 248 SCD patients (189 SS homozygotes; 8 SD heterozygote; 2 SC heterozygotes;49 Sβ+ Thal double heterozygotes), with a median age of 22 years (22.1 ± 9.1; Mean ± SD). 129(52%) were males. Blood was collected for several biochemical investigations, including total serum bilirubin. DNA was isolated from peripheral blood leucocytes by standard methods.UGT1A1 (TA)n promoter length variability was genotyped by polymerase chain reaction using previously described primers. Additionally, several other polymorphisms namely −3440C>A; −3401T>C; −3729T>G; −3154G>A & +211G>A were also studied by direct sequencing with appropriate primers to study the UGT1A1 haplotypes.

Results: Amongst 248 patients analyzed, 100(40%) were homozygous for (AT)6UGT1A1 allelle;114(46%) were heterozygous for (AT)6 and (AT)7 alleles and 23(9%) were homozygous for the (AT)7 allele. Mean serum bilirubin was significantly higher in the homozygous (AT)7 group as compared to the (AT)6 group(47.7 v/s 23.4; p <0.001). Furthermore, the mean serum bilirubin concenterations were also higher in −3440AA homozygotes, −3279GG homozygotes, and −3154AA homozygotes respectively when compared to the relative wild alleles.

Total serum bilirubin, hematological parameters and UGT1A1 gene polymorphisms in Omani SCD patients

No. of PatientsHb(Mean ± SD)Retic (Mean ± SD)HbF (Mean ± SD)Total Bilirubin(Mean ± SD)p values
SIG– Significant; NS–Not Significant 
(AT)6/6 96 9.57 ±1.34 229 ± 88 8.2 ± 6.0 23.4 ± 12.8  
(AT)7/7 22 9.55 ± 1.91 263 ± 138 11.0 ± 7.9 47.7 ± 45.2 <0.001[SIG] 
−3440 CC 200 9.52 ± 1.42 233 ± 104 8.8 ± 6.8 28.4 ± 21.9  
−3440 AA 2 8.3 ± 0.28 296 ± 47 2.4 ± 1.3 31.0 ± 1.31 0.868[NS] 
−3279 TT 36 9.94 ± 1.34 224 ± 98 10.0 ± 7.2 21.8 ± 14.9  
−3279 GG 62 9.21 ± 1.78 258 ± 128 7.1 ± 6.2 38.3 ± 33.0 0.005[SIG] 
−3145 GG 95 9.52 ± 1.48 234 ± 91 7.9 ± 6.1 23.6 ± 13.3  
−3154 AA 20 9.29 ± 1.59 264 ± 130 10.0 ± 5.9 48.7 ± 43.2 <0.001[SIG] 
No. of PatientsHb(Mean ± SD)Retic (Mean ± SD)HbF (Mean ± SD)Total Bilirubin(Mean ± SD)p values
SIG– Significant; NS–Not Significant 
(AT)6/6 96 9.57 ±1.34 229 ± 88 8.2 ± 6.0 23.4 ± 12.8  
(AT)7/7 22 9.55 ± 1.91 263 ± 138 11.0 ± 7.9 47.7 ± 45.2 <0.001[SIG] 
−3440 CC 200 9.52 ± 1.42 233 ± 104 8.8 ± 6.8 28.4 ± 21.9  
−3440 AA 2 8.3 ± 0.28 296 ± 47 2.4 ± 1.3 31.0 ± 1.31 0.868[NS] 
−3279 TT 36 9.94 ± 1.34 224 ± 98 10.0 ± 7.2 21.8 ± 14.9  
−3279 GG 62 9.21 ± 1.78 258 ± 128 7.1 ± 6.2 38.3 ± 33.0 0.005[SIG] 
−3145 GG 95 9.52 ± 1.48 234 ± 91 7.9 ± 6.1 23.6 ± 13.3  
−3154 AA 20 9.29 ± 1.59 264 ± 130 10.0 ± 5.9 48.7 ± 43.2 <0.001[SIG] 
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Summary/Conclusions: Apart for the UGT1A1 (AT)7 homozygosity, −3729GG homozygosity, −3154AA homozygosity were significantly associated with raised total bilirubin levels. This study did not find any statistically significant association between −3440 C>A, −3401T>C and +211G>A polymorphisms and the bilirubin levels in Omani SCD patients.

Topics:
genes, polymorphism, sickle cell anemia, udp-glucuronosyltransferase 1a1, bilirubin, serum bilirubin level, serum bilirubin measurement, anemia, hemolytic, congenital, chief complaint, dna

Author notes

Disclosure: No relevant conflicts of interest to declare.

2007, The American Society of Hematology
2007
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