This gene dosage effect of PKD1 has been reported in humans with ADPKD and mouse models of the disease18 and is supported by the more severe phenotype observed in 20-day-old RC/null mice compared with the phenotype observed in 6−7-month-old RC/RC mice (Figs. 3, 4). This evidence concerns the gene PKD1 and autosomal dominant polycystic kidney disease.