PKHD1 and autosomal recessive polycystic kidney disease: ARPKD is caused by dysfunction of primary cilia15 due to mutations within polycystic kidney and hepatic disease-1 (PKHD1), which encodes a 4074 amino acid multi-domain transmembrane protein (fibrocystin/polyductin, FPC) that is expressed in the primary cilia of renal tubular epithelial cells and cholangiocytes16,17.