PKD2 and cystic kidney disease: In autosomal dominant polycystic kidney disease (ADPKD), primary ciliary dysfunction due to mutations in the PKD1 (polycystin-1; PC1) and PKD2 (polycystin-2; PC2) genes, which encode the polycystin 1 and polycystin 2 Ca2+ ion channels expressed in the surface of primary cilia, respectively, result in tubular epithelial cell-derived renal cysts.