Progress, challenges, and pragmatic concessions in predicting relative risk of kidney survival in ARPKD.

Autosomal recessive polycystic kidney disease is rare, with heterogeneous disease progression toward kidney failure. Risk stratification tools are needed to identify patients at higher risk of progression. Burgmaier et al. developed a relative risk score model in the international ARPKD registry for children older than 2 months of age without kidney failure. Their regression-based model included 5 predictors and yielded a simple prognostic score that classified "lower-risk" and "higher-risk" groups. Discrimination separating these 2 groups was good, but there are potential future opportunities for absolute risk prediction. We discuss considerations for the interpretation of relative risk scores and external validation of prediction models in rare diseases like autosomal recessive polycystic kidney disease.