PKD1 and ciliopathy: ADPKD is classified as a ciliopathy (29), based on the obligate functional heterodimerization of PC1 and PC2 on cell cilia, where PC1 normally acts as a flow sensor to trigger the calcium channel activity of PC2: calcium influx and other signaling interactions of the PC1/PC2 heterodimer act to restrain cell growth and govern the polarity of cell division in normal cells (30).