Mechanisms of cyst expansion in ADPKD and the associated increase in TKV are based on reduced intracellular Ca2+ influx caused by mutations in either PKD1 or PKD2, increased cellular adenosine 3′, 5′-cyclic monophosphate (cAMP) levels, and aberrant Ras/Raf/ERK activation [18]. The gene discussed is PKD2; the disease is cyst.