Wilson disease is a single gene disorder - comprehensive analysis of patients with prior negative genetic testing

Wilson disease (WD) is an autosomal recessive disorder caused by damaging ATP7B variants. Up to 20% of clinically diagnosed cases remain genetically unexplained. We aimed to analyze patients with WD (Leipzig score ≥4) with zero or one known ATP7B variant using state-of-the-art methods.

Among 761 patients from four WD cohorts previously screened for ATP7B variants, 44 with zero or one known variant in ATP7B were sequenced by current best practice methods (whole genome sequencing) and the data were analyzed in a stepwise approach: first searching for pathogenic variants in ATP7B, then in 97 copper-related genes, and finally in 4,304 genes linked to liver or neurological diseases. If unsolved, long-read ATP7B sequencing and/or ATP7B protein surrogate peptide analysis was conducted when possible.

A total of 5.8% of patients had zero or only one known variant in ATP7B. Median (range) Leipzig score was 6 (4-11). Primary presentations at diagnosis were hepatic (24), neurologic (12), or mixed (8). Genetic analysis of ATP7B resolved 52% (23/44) of cases: 7 through reclassification of previously reported findings and 16 by whole genome sequencing detecting previously unreported ATP7B variants. ATP7B peptide measurement detected six additional patients with ATP7B protein defects, supporting pathogenicity of variants. Together, these methods confirmed ATP7B dysfunction in 66% (29/44). In our entire cohort, this corresponded to genetic confirmation in 98% (746/761). Comprehensive screening of other genes did not identify alternative genetic causes.

Our comprehensive data strongly support WD as a single-gene disease. Genetic reevaluation, ATP7B resequencing, and peptide analysis should be performed in unresolved cases.

This work addresses the molecular diagnostic gap in clinically confirmed Wilson disease by demonstrating that most genetically unresolved cases can be explained by previously undetected or misclassified ATP7B variants when modern genomic and functional approaches are applied. The findings are particularly relevant for clinicians and patients facing diagnostic uncertainty, as they reinforce Wilson disease as a single-gene disorder rather than a genetic heterogeneous condition. Practically, the study supports routine genetic reevaluation using contemporary whole-genome sequencing and targeted functional assays in unresolved cases, improving diagnostic certainty, genetic counseling, and cascade testing. While some advanced analyses were not feasible in all patients, the results highlight the value of revisiting negative genetic findings before considering alternative diagnoses.