Antisense oligonucleotides rescue an intronic splicing variant in the ABCB11 gene that causes progressive familial intrahepatic cholestasis type 2

Background: Progressive familial intrahepatic cholestasis type 2 (PFIC2) is a rare disorder caused by vari-ants in the ABCB11 gene encoding the bile salt export pump (BSEP). We investigated the molecular defect in a PFIC2 infant and rescued the splicing defect with antisense oligonucleotides (ASOs).Methods: Whole-exome sequencing (WES) revealed compound heterozygous variants in the ABCB11 gene in a PFIC2 patient. Liver biopsy was immunostained for BSEP. The splicing effect of the candidate variants was investigated by minigene assay . ASOs were designed to rescue aberrant splicing.Results: A Chinese girl of two nonconsanguineous healthy parents suffered from low glutamyl transpep-tidase cholestasis and showed no response to the ursodeoxycholic acid. WES revealed that the patient was compound heterozygous for two novel variants in the ABCB11 gene: c.76 + 29T > G and c.390-2A > G. Liver immunohistochemistry showed the absence of BSEP. The variant c.76 + 29T > G was confirmed to re-tain 42 bp in the mature mRNA. The variant c.390-2A > G was confirmed to cause exon 6 skipping. We designed two ASOs and identified one of them that efficiently induced pseudoexon exclusion.Conclusion: We reported two novel variants of the ABCB11 gene, c.76 + 29T > G and c.390-2A > G, in a PFIC2 infant, thereby expanding the genotype of PFIC2. Our findings provide evidence for ASOs as a therapeutic approach for PFIC2 patients carrying intronic variants.(c) 2022 Published by Elsevier Ltd on behalf of Editrice Gastroenterologica Italiana S.r.l.