PKHD1 and cholangiocarcinoma: Conversely, ARPKD is the result of mutations in PKHD1, whose protein polyductin is not known to increase the risk for malignancy, yet cases of cholangiocarcinoma have been reported in adults with ARPKD (Fonck, Chauveau, Gagnadoux, Pirson, & Grünfeld, 2001).