Molecular genetics of hyperbilirubinemia in neonatal cases from Malta

Abstract

Neonatal hyperbilirubinemia and resultant jaundice are extremely common, affecting up to 80% of neonates. Although, generally a benign postnatal transitional phenomenon, a select number of infants develop potentially life-threatening levels of total serum bilirubin. The persistence level of hyperbilirubinemia can be due to variations in genes involved in the metabolic pathway of bilirubin including; the uridine diphosphate glucuronosyltransferase (UGT1A1) gene, more specifically the UGT1A1*28 and UGT1A1*6 polymorphisms, amongst other variants and solute carrier organic anion transporter family member 1B1 (SLCO1B1) gene, more specifically the; c.388G>A, c.463C>A and c.521T>C variants. The UGT1A1 gene encodes a UDP-glucuronosyltransferase, the sole enzyme responsible for catalysing the glucuronidation pathway which generates water-soluble bilirubin glucuronides. Hence, variations in this gene lead to deficiencies in bilirubin conjugation and excretion. The SLCO1B1 gene encodes for OATP1B1 protein transporter, responsible for the intracellular hepatic uptake of bilirubin. Thus, variations in this gene result in deficient uptake and intrahepatic storage of bilirubin. This study focused on the genotyping of four UGT1A1 gene variants and three SLCO1B1 variants on a collection of 409 selected Maltese neonates with reported severe hyperbilirubinemia in years 2014-2017, by means of RFLP-PCR. After performing multiple statistical analysis, no significant association was found between the total serum bilirubin average and first reading and genotype status. However, interestingly when comparing the allelic and haplotype frequencies in the Maltese case population, they were almost identical to the African population as opposed to the European population. This warrants further investigation to assess the role of UGT1A1 and SLCO1B1 in biochemical abnormalities so that new therapeutic approaches for treatment can be established.