Genotype-phenotype relationships of truncating mutations, p.E297G and p.D482G in bile salt export pump deficiency.
DOI: 10.1016/j.jhepr.2022.100626; PMCID: PMC9852554
Background & aims: Bile salt export pump (BSEP) deficiency frequently necessitates liver transplantation in childhood. In contrast to two predicted protein truncating mutations (PPTMs), homozygous p.D482G or p.E297G mutations are associated with relatively mild phenotypes, responsive to surgical interruption of the enterohepatic circulation (siEHC). The phenotype of patients with a compound heterozygous genotype of one p.D482G or p.E297G mutation and one PPTM has remained unclear. We aimed to assess their genotype-phenotype relationship.
Methods: From the NAPPED database, we selected patients with homozygous p.D482G or p.E297G mutations (BSEP1/1; n = 31), with one p.D482G or p.E297G, and one PPTM (BSEP1/3; n = 30), and with two PPTMs (BSEP3/3; n = 77). We compared clinical presentation, native liver survival (NLS), and the effect of siEHC on NLS.
Results: The groups had a similar median age at presentation (0.7-1.3 years). Overall NLS at age 10 years was 21% in BSEP1/3 vs. 75% in BSEP1/1 and 23% in BSEP3/3 (p < 0.001). Without siEHC, NLS in the BSEP1/3 group was similar to that in BSEP3/3, but considerably lower than in BSEP1/1 (at age 10 years: 38%, 30%, and 71%, respectively; p = 0.003). After siEHC, BSEP1/3 and BSEP3/3 were associated with similarly low NLS, while NLS was much higher in BSEP1/1 (10 years after siEHC, 27%, 14%, and 92%, respectively; p < 0.001).
Conclusions: Individuals with BSEP deficiency with one p.E297G or p.D482G mutation and one PPTM have a similarly severe disease course and low responsiveness to siEHC as those with two PPTMs. This identifies a considerable subgroup of patients who are unlikely to benefit from interruption of the enterohepatic circulation by either surgical or ileal bile acid transporter inhibitor treatment.
Impact and implications: This manuscript defines the clinical features and prognosis of individuals with BSEP deficiency involving the combination of one relatively mild and one very severe BSEP deficiency mutation. Until now, it had always been assumed that the mild mutation would be enough to ensure a relatively good prognosis. However, our manuscript shows that the prognosis of these patients is just as poor as that of patients with two severe mutations. They do not respond to biliary diversion surgery and will likely not respond to the new IBAT (ileal bile acid transporter) inhibitors, which have recently been approved for use in BSEP deficiency.
ABCB11, ATP-binding cassette, sub-family B member 11; ALT, alanine aminotransferase; AST, aspartate aminotransferase; BSEP; BSEP, bile salt export pump; ChiLDReN, Childhood Liver Disease Research Network; GGT, gamma-glutamyltransferase; HCC, hepatocellular carcinoma; LTx, liver transplantation; NAPPED, NAtural course and Prognosis of PFIC and Effect of biliary Diversion; NLS, native liver survival; PFIC2; PFIC2, progressive familial intrahepatic cholestasis type 2; PPTM, predicted protein truncating mutation; REDCap, Research Electronic Data Capture; TSB, total serum bilirubin; UDCA, ursodeoxycholic acid; compound heterozygosity; genotype; interruption of the enterohepatic circulation; phenotype; sBAs, serum bile acids; siEHC, surgical interruption of the enterohepatic circulation
Felzen A, van Wessel DBE, Gonzales E, et al. Genotype-phenotype relationships of truncating mutations, p.E297G and p.D482G in bile salt export pump deficiency. JHEP Rep. 2022;5(2):100626. Published 2022 Nov 16. doi:10.1016/j.jhepr.2022.100626
This is an open access article distributed under the terms of the Creative Commons CC-BY license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Publisher's Link: https://www.jhep-reports.eu/article/S2589-5559(22)00198-7/fulltext