ADPKD etiopathogenesis derives from two distinct and sequential processes: (i) an initiating event in which the PKD1/PKD2 functional activity falls below a critical threshold, triggering a cascade of signaling events; and (ii) cyst growth mediated by cellular proliferation, fluid secretion, and extracellular matrix deposition. The gene discussed is PKD2; the disease is autosomal dominant polycystic kidney disease.