A novel ancestral splicing mutation in the multidrug resistance protein 2 gene causes Dubin-Johnson syndrome in Ashkenazi Jewish patients

Dubin-Johnson syndrome (DJS) is an inherited disorder characterized by chronic conjugated hyperbilirubinemia due to the absence or dysfunction of the multidrug resistance protein 2 (MRP2). We previously identified two distinct ancestral mutations causing DJS in 22 unrelated Iranian and five unrelated Moroccan Jewish patients, respectively. In this study we identified and characterized the mutation causing DJS in Ashkenazi Jewish patients and assessed a possible founder effect. Sequencing of all 32 exons of the MRP2 gene identified a novel IVS8 + 4A → G mutation in three unrelated homozygotes. Haplotype analysis using four intragenic dimorphisms disclosed a founder effect for the mutation. RT-PCR and real time PCR analysis of mRNA from one patient revealed three splice variants all leading to frameshifts and predicting premature termination codons. The main splice variant was a consequence of the use of a cryptic donor splice site inside exon 8. Liver biopsy in one patient revealed complete absence of MRP2 from the canalicular membrane of hepatocytes. In conclusion, our results provide strong evidence that an ancestral IVS8 + 4A → G mutation causes DJS in Ashkenazi Jewish patients by abolishing normal splicing of intron 8 leading to aberrantly spliced products that predict truncation of MRP2.