Relationship between Total Kidney Volume and eGFR in Autosomal Dominant Polycystic Kidney Disease

In autosomal dominant polycystic kidney disease, there is a linear relationship between the log-transformed total kidney volume and eGFR. There is a predictable change in the rate of eGFR decline with reduction in kidney growth rate. This framework can be used to determine treatment effect to support accelerated approval of drugs for polycystic kidney disease.

Total kidney volume (TKV) is accepted by the US Food and Drug Administration as a surrogate end point that is reasonably likely to predict clinical benefit in autosomal dominant polycystic kidney disease and the most commonly used response biomarker for proof-of-concept intervention trials. However, the magnitude of treatment effect on TKV that would be predictive of a meaningful improvement in a clinical outcome, such as eGFR, is unknown. Inference of this from observational studies has previously been approached by examining interindividual variance in the relationship between TKV and GFR slopes over time.

We developed a novel approach to modeling the intraindividual relationship between TKV and eGFR. Patients from the Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease and Halt Progression of Polycystic Kidney Disease Study A dataset were stratified by Mayo Imaging Class (MIC). Linear mixed models were fitted to eGFR with a fixed effect of log(TKV) and random intercepts, and the average slope within each MIC was estimated.

We found that within each MIC, there is a consistent, linear relationship between log(TKV) and eGFR. The model predicts that within classes 1C-1E, for each 1% point per year reduction in TKV growth rate, the rate of eGFR decline would be reduced by 0.40-0.52 ml/min per 1.73 m 2 per year.

We have developed a new model that provides a framework for defining the magnitude of treatment effect on TKV that would support accelerated approval of a drug for autosomal dominant polycystic kidney disease.