Potential explanations for this include that these cases had an unannotated second variant (perhaps hypomorphic rather than truly pathogenic); they had somatic mosaicism for a second pathogenic PKHD1 allele; they had an alternative cause for hepatic fibrosis; or that monoallelic PKHD1 variants can manifest with this phenotype. This evidence concerns the gene PKHD1 and Hepatic fibrosis.