Among patients with a clinical and imaging-based diagnosis of autosomal dominant polycystic kidney disease (ADPKD), a negative family history for ADPKD (FH−) has been reported in 10%1 and 14.2%2 (this proportion is 27.8% in a broader PKD population3). Clinical reasons for an FH− are unavailable information about the biological parents and undiagnosed mild or variable ADPKD associated with de novo mutations.1-3 The genetic causes for clinically variable ADPKD include locus heterogeneity (PKD1, PKD2, and GANAB), allelic heterogeneity (truncating and nontruncating mutations), hypomorphic alleles, mosaicism, modifier genes, and rare combinations of these.