PIK3C2A and autosomal recessive polycystic kidney disease: We note that in both human PKHD1-related disease and the Cys1cpk/cpk mouse model of ARPKD, cystic disease is initiated in the fetal proximal tubule and transitions to collecting duct dilation as the predominant lesion in the perinatal period (Nakanishi et al., 2000).