PKHD1 and autosomal dominant polycystic kidney disease: In humans, loss of function in polycystin 1 (PC1) and polycystin 2 (PC2) cause autosomal dominant PKD (ADPKD) (Saigusa and Bell 2015), whereas loss of function in fibrocystin/polyductin causes autosomal recessive PKD (ARPKD) (Guay-Woodford et al.