Clinical Exome Sequencing in Unexplained Hyperferritinemia Reveals Digenic and Oligogenic Inheritance Beyond Iron...

Hyperferritinemia encompasses heterogeneous genetic etiologies beyond HFE-related hemochromatosis. Current guidelines recommend testing for rare hemochromatosis genes, yet no consensus exists on comprehensive genomic approaches. We aimed to characterise the genetic landscape of unexplained hyperferritinemia using clinical exome sequencing (CES) and evaluate genotype-phenotype correlations across functional pathways.

In this retrospective study (2019-2024), consecutive patients with unexplained hyperferritinemia after exclusion of secondary causes underwent CES. Patients with known HFE p.Cys282Tyr homozygosity were not referred for CES. Variant filtering was performed using the Genomics England panel for iron metabolism and the French network for rare liver diseases panel, combined with phenotype-driven analysis based on Human Phenotype Ontology annotations for iron-related phenotypes. Genes were categorised into four pathways: systemic iron sensing, iron transport and storage, hepatic metabolism and erythropoiesis.

Among 108 patients, CES identified at least one variant in 72 (66.7%), including 44 (40.7%) with likely pathogenic or pathogenic (LP/P) variants. HFE was the most frequently affected gene, followed by SERPINA1, ATP7B, and CP. Among patients without monogenic HFE alterations (n = 57), 21 (36.8%) carried variants, mainly affecting CP, ATP7B, SERPINA1 or GBA. Digenic or oligogenic inheritance was observed in 30.6% (22/72) of patients overall and in 20.5% (9/44) of those carrying LP/P variants, most frequently involving HFE-SERPINA1 and HFE-ATP7B combinations. Cross-pathway combinations occurred in 17 of 22 digenic patients (77.3%). The systemic iron sensing group exhibited significantly higher serum iron (p = 0.009) and transferrin saturation (p = 0.008).

CES reveals genetic heterogeneity beyond the traditional Mendelian framework, with frequent non-HFE gene involvement and digenic inheritance and should be considered after exclusion of HFE p.Cys282Tyr homozygosity.