The fact that we did not find genetic mutations nor epigenetic alterations in PKD1 could mean that a second hit did not occur in PKD1 or PKD2, but that merely the germline mutation leads to haploinsufficiency which is in line with previous findings that Pkd1+/− mice develop a cystic phenotype when renal injury is induced.20 Alternatively, a second hit in PKD1 may have occurred in the cyst but was lost during culture of the primary TECs used in this study. The gene discussed is PKD2; the disease is cyst.