Intrafamilial Variability of ADPKD

Introduction: Discordance in kidney disease severity between affected relatives is a recognized feature of autosomal dominant polycystic kidney disease (ADPKD). Here, we report a systematic study of a large cohort of families to define the prevalence and clinical features of intrafamilial discordance in ADPKD. Methods: The extended Toronto Genetic Epidemiology Study of Polycystic Kidney Disease (eTGESP) cohort includes 1390 patients from 612 unrelated families with ADPKD ascertained in a regional polycystic kidney disease center. All probands underwent comprehensive PKD1 and PKD2 mutation screening. Total kidney volume by magnetic resonance imaging (MRI) was available in 500 study patients. Results: Based on (i) rate of estimated glomerular filtration rate (eGFR) decline, (ii) age at onset of end-stage renal disease (ESRD), and (iii) Mayo Clinic Imaging Classification (MCIC), 20% of patients were classified as having mild disease, and 33% as having severe disease. Intrafamilial ADPKD discordance with at least 1 mild and 1 severe case was observed in 43 of 371 (12%) families, at a similar frequency regardless of the responsible gene (PKD1/PKD2/no mutation detected) or mutation type (protein-truncating versus nontruncating). Intrafamilial discordance was more common in larger families and was present in 30% of families with more than 5 affected members. The heritability of age at onset of ESRD was similar between different mutation types. Conclusion: Extreme kidney disease discordance is present in at least 12% of families with ADPKD, regardless of the underlying mutated gene or mutation class. Delineating genetic and environmental modifiers underlying the observed intrafamilial ADPKD variability will provide novel insights into the mechanisms of progression in ADPKD.