Only a handful of individual cysts from ADPKD patients have been genetically investigated, and while the results were interpreted to suggest that second hit mutations are largely inactivating mutations (86), the genetic data does not necessarily agree with studies investigating PC1 expression on the protein level in which overexpression of PC1 was observed (87, 88, 89). This evidence concerns the gene PKD1 and autosomal dominant polycystic kidney disease.