PKHD1 and autosomal recessive polycystic kidney disease: ARPKD is caused by mutations in the PKHD1 gene, which maps to chromosome 6p21.1-p12. PKHD1 is amongst the largest genes in humans with 66 coding exons [5] and encodes a 4074-amino acid protein named fibrocystin/polyductin (FC/PD).