[OATP 1B1 T521C/A388G is an important polymorphism gene related to neonatal hyperbilirubinemia]

Multiple genetic and environmental factors contribute to the onset of many human diseases, such as neonatal hyperbilirubinemia. OATP 1B1 is an important polymorphism gene which transmembrane transports unconjugated bilirubin(UCB). Genetic polymorphisms that affect the functionality of the protein may potentially lead to altered transport characteristics. The T521C/A388G polymorphism of this gene has been reported to considerably reduce the transporting property of drugs like pravastatin, and may be involved in the membrane translocation of bilirubin. Some studies have shown that OATP 1B1 mediates bilirubin uptake from blood into the liver, and the OATP 1B1 polymorphism is a likely mechanism explaining the differences of bilirubin level in peripheral blood. The aim of this study was to evaluate the relationship between OATP 1B1 polymorphisms and neonatal hyperbilirubinemia.

A total of 220 newborn infants with hyperbilirubinemia were recruited from Hunan Children Hospital from November 2008 to December 2009 according to the diagnostic criteria. Age and sex matched control subjects comprised of 200 unrelated, hyperbilirubinemia-free newborns. Biochemical and clinical data were collected from the case history. One ml venous blood samples in EDTA vials were taken from each subject and DNA was isolated from peripheral leukocytes by standard methods, preserved in 4°C. 1 - 2 ml venous blood samples were also taken for detecting the serum total bilirubin and direct bilirubin level by chemical oxidation method. OATP 1B1 T521C/A388G polymorphisms were determined using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Allele and genotype frequencies were compared between patients and control. The gene polymorphism and risk of disease were also analyzed. Serum total bilirubin, conjugated bilirubin and unconjugated bilirubin levels were compared between different OATP 1B1 T521C/A388G genotypes.

Allele frequencies in patients and control population were in Hardy-Weinberg equilibrium (P > 0.05). Allele and genotype frequencies of the OATP 1B1 T521C polymorphism in patients were significantly different from the controls. The OATP 1B1 521C allele frequency was only 8.2% in patients, while reached 14.0% in the control group which was very close to the frequency of common Chinese people. However, the proportion of wild type genotypes was significantly higher than those of the controls, reached 84.1%. The 521 C allele and genotypes carrying 521 C allele illustrated low risk for neonatal hyperbilirubinemia (OR = 0.530, 95%CI = 0.328 - 0.857; OR = 0.541, 95%CI = 0.344 - 0.851). However, the frequencies of alleles and genotypes of SLCO1B1 A388G did not differ significantly from those of the controls, and this polymorphism did not influence susceptibility to such disease. Among the three OATP 1B1 A388G genotypes, the level of total serum bilirubin (TSB), direct bilirubin (DB) and unconjugated bilirubin (UCB) were significantly different. Values of TSB, DB and UCB were the highest in wild type subjects, lower in heterozygotes, and the lowest in mutant homozygotes. TSB and UCB in patients with wild type genotypes reached 602.5 µmol/L and 585.0 µmol/L respectively, nearly twice the average value of homozygous patients. While the TSB and UCB in homozygotes were below the average value of all patients, only 351.7 µmol/L and 338.8 µmol/L respectively.

Our findings indicated that OATP 1B1 A388G polymorphism has a notable influence on the serum bilirubin level in neonatal hyperbilirubinemia patients. The OATP 1B1 521T allele may be a potential risk factor of such disease. OATP 1B1 T521C/A388G was an important polymorphism gene which related with neonatal hyperbilirubinemia. Future study should involve other polymorphisms of OATP 1B1, more candidate genes and environmental risk factors. It is also necessary to investigate their association with the severity and prognosis of this disease in order to elucidate the genetic pathogenesis of neonatal hyperbilirubinemia as a complex disease. This study should be repeated in a larger population and different ethnic groups.