The impact of a secondary, rare, non-pathogenic PKD1 variant on disease progression in autosomal dominant polycystic kidney disease

Background: Autosomal dominant polycystic kidney disease (ADPKD) is caused primarily by pathogenic variants in the PKD1 and PKD2 genes. Although the type of ADPKD variant can influence disease severity, rare, hypomorphic PKD1 variants have also been reported to modify disease severity or cause biallelic ADPKD. This study examines whether rare, additional, potentially protein-altering, non-pathogenic PKD1 variants contribute to ADPKD phenotypic outcomes. Methods: We investigated the prevalence of rare, additional, potentially protein-altering PKD1 variants in patients with PKD1-associated ADPKD. The association between rare, additional, potentially protein-altering variants and phenotypic outcomes, including progression to kidney failure, age at onset of hypertension and urological events, height-adjusted total kidney volume, and predicting renal outcomes in PKD (PROPKD) score, were examined. Results: Rare, additional, potentially protein-altering variants were detected in 6% of the 932 ADPKD patients in the study. The presence of rare, additional, potentially protein-altering variants was associated with 4 years earlier progression to kidney failure (hazard ratio (HR): 1.66; 95% confidence interval (CI): 1.18–2.34; P = 0.003), with in-trans rare, additional, potentially protein-altering variants (n = 13/894) showing a greater risk of kidney failure (HR: 1.83; 95% CI 1.00–3.33; P = 0.049). We did not detect statistically significant differences between rare, additional, potentially protein-altering variants and other phenotypic outcomes compared to those without rare, additional, potentially protein-altering variants. Conclusions: In patients with PKD1-associated ADPKD, our findings suggest that rare, additional, potentially protein-altering variants in PKD1 may influence disease severity. These findings have potential clinical implications in counselling and treating patients with rare, additional, potentially protein-altering variants, but further investigation of such variants in larger, longitudinal cohorts with detailed, standardised phenotype data is required.