Remarkably, the increase in renal fibrosis promoted by smoking was much higher in cystic than noncystic mice, revealing positive interaction between smoking and Pkd1 deficiency (P = 0.003) [0.09% (0.04–0.09) in NC, 0.13% (0.09–0.19) in NCS, 0.25% (0.20–0.66) in CY, and 1.20% (0.88–1.92) in CYS]. The gene discussed is PKD1; the disease is renal fibrosis.