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Kidney Week

Abstract: TH-OR37

Comparative PKD1 and PKD2 Missense Variant Profiling Aids Molecular Diagnoses Across the ADPKD Spectrum and Reveals Common Pathomechanisms

Session Information

Category: Genetic Diseases of the Kidneys

  • 1001 Genetic Diseases of the Kidneys: Cystic

Authors

  • Sieben, Cynthia J., Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Gainullin, Vladimir, Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Heyer, Christina M., Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Dillinger, Elizabeth K., Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Thao, Ka, Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Sturmlechner, Ines, Mayo Clinic Research Rochester, Rochester, Minnesota, United States
  • Harris, Peter C., Mayo Clinic Research Rochester, Rochester, Minnesota, United States
Background

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the formation and growth of fluid-filled renal cysts, often leading to kidney failure. Typically, monoallelic PKD1 or PKD2 variants cause ADPKD, however, complex inheritance and a broad phenotypic spectrum also exist. The advent of genomewide variant screening has emphasized the importance of ADPKD molecular diagnostic methods to reliably determine the pathogenicity of variants of unknown significance (VUS).

Methods

Here, we developed a cell-based flow cytometry assay to assess the pathogenicity of PKD1 and PKD2 VUS. This assay utilizes localization of polycystin 1 (PC1; encoded by PKD1) to the apical plasma membrane, where formation of the PC1/PC2 complex (PC2; encoded by PKD2) is required for proper PC1 trafficking. Employing this assay, we have assessed 48 PKD1 and 44 PKD2 variants with predicted pathogenicity ranging from fully penetrant monoallelic, to incompletely penetrant biallelic, and likely benign variants.

Results

The majority of likely pathogenic monoallelic PKD1 and PKD2 missense variants perturb PC1 trafficking by >80%, with a correlation between the predicted penetrance (determined bioinformatically) and surface PC1. In cis monoallelic PKD1 variants have an additive effect and perturb PC1 trafficking by 60-98%, whereas proposed biallelic PKD1 variants exhibit variable impacts (0-70% perturbation; majority <60%). In contrast, likely benign variants have little or no impact. To understand mechanisms underlying aberrant PC1 trafficking, we evaluated defective protein folding under enhanced folding conditions (reduced culture temperature; 30°C). The majority of PKD1 and PKD2 monoallelic, and all PKD1 and PKD2 complex variants impact PC1 or PC2 folding, and can be partially or fully rescued at 30°C.

Conclusion

These studies describe a novel in vitro assay for determining PKD1 and PKD2 VUS pathogenicity, and highlight a continuum of allele penetrance across the ADPKD spectrum. This firmly establishes PC1 trafficking as a common PKD1/PKD2-mediated ADPKD pathomechanism, but suggests that other mechanisms account for a minority of variants. Further, demonstrated aberrant PC1 or PC2 folding suggests a role for chaperone therapy in ADPKD.

Funding

  • NIDDK Support