Background: Neonatal hyperbilirubinemia is a common problem in neonates and affects 60% of Asian newborn babies which is twice that found in Caucasians. These findings suggest that a genetic factor might be involved. Recently, a relationship between polymorphisms of the bilirubin uridine 5 diphosphate-glucuronosyltransferase (UGT1A1) gene and neonatal hyperbilirubinemia has been reported. It was demonstrated that the genetic variations cause a decrease in UGT1A1 activity in neonates, leading to an accumulation of unconjugated bilirubin in serum. However, in Asians the G to A missense mutations in the UGT1A1 at nucleotide 211 (known as G71R), were the predominant findings. Therefore, the impact of this polymorphism on serum bilirubin in healthy Thai neonates is of interest.
Objective: The aim of the present study was to investigate the frequency of UGT1A1 allele in healthy Thai neonates and to determine its role in neonatal hyperbilirubinemia.
Material and Method: A cross sectional study was conducted to investigate an association between the UGT1A1 G71R polymorphism and neonatal hyperbilirubinemia. Cord blood of 291 neonates was obtained to determine the gene frequency of UGT1A1 G71R by PCR-restriction fragment length polymorphism method. During the first 48 to 72 hours of the infants’ life, the infants’ blood was collected to measure their microbilirubin.
Results: PCR-RFLP analysis revealed the UGT1A1 G71R polymorphism in 42 infants (14.4%). In addition, six of this group (14.3%) had a microbilirubin level more than 95th percentile which was approximately 2.5 times more than those with the wild type allele (5.6%). The maximum microbilirubin level of infants in the R71 allele group was significantly higher than those in the G71 allele group, (11.79 + 3.34 mg/dL and 9.53 + 2.34 mg/dL, respectively, p < 0.01).
Conclusion: In the present study, the UGT1A1 G71R allele was found to be one of the risk factors for neonatal hyperbilirubinemia in Thai neonates.

Keywords: neonatal hyperbilirubinemia, UGT1A1, G71R, microbilirubin