Genotype-Phenotype Correlations of Monoallelic PFIC Variants in Pediatric Liver Disease: A Multicenter Retrospective Cohort Study.

Progressive familial intrahepatic cholestasis (PFIC) is classically caused by biallelic pathogenic variants, yet monoallelic variants of uncertain significance (VUS) in PFIC-associated genes are increasingly identified in children with cholestasis, creating diagnostic uncertainty. We conducted a multicenter cohort study of children with liver disease and/or cholestasis harboring monoallelic VUS in ATP8B1, ABCB11, ABCB4, TJP2, or NR1H4. Clinical and longitudinal data were analyzed, and variant frequencies were compared with population data from gnomAD. Twenty-six children with 37 monoallelic PFIC-gene VUS met inclusion criteria, and multigenic variant burden was common (73.1%). PFIC-like biochemical patterns were observed in 42.3% but were frequently transient, and no patient met criteria for monogenic PFIC on longitudinal follow-up. Severe liver outcomes, including transplantation in two patients, occurred in a subset of patients with ABCB4 and/or ATP8B1 VUS and multigenic burden, along with competing clinical factors. Among 22 variants with population data, 11 (50%) demonstrated significant enrichment after multiple-testing correction, most commonly involving ABCB4. These findings suggest that monoallelic PFIC-associated variants currently classified as VUS are unlikely to represent monogenic disease drivers in isolation and may instead contribute within multigenic or susceptibility-based contexts. Population-level enrichment, particularly involving ABCB4, further supports careful phenotype-anchored, longitudinal interpretation in pediatric liver disease.