PKD2 and autosomal dominant polycystic kidney disease: It is found that causative gene proteins in three human PKDs (PKD1, PKD2, and ARPKD) are associated with primary cilia and the related structures, and it is inferred that structural abnormality and dysfunction of the primary cilia cause disease, and it is a theoretical rationale for the common pathophysiological mechanism of ARPKD and ADPKD.