Autosomal recessive polycystic kidney disease (ARPKD) is a severe renal cystic disease mainly caused by PKHD1. However, its genetic cause, pathological features, and mechanism remained unsolved. Our findings may provide new insight on the pathophysiology of the polycystic kidney due to PKHD1 deficiency, and the PKHD1 mosaicism needs to be taken close attention in genetic testing of ARPKD.