The most widely studied mouse model of ARPKD, the cpk mouse carries a spontaneous insertion/deletion (indel) mutation in the Cys1 gene, encoding the cystin protein (Hou et al., 2002; Guay-Woodford, 2003; Nagao et al., 2012). Here, PIK3C2A is linked to autosomal recessive polycystic kidney disease.