AP1S1 and MEDNIK syndrome: Gene screening for the diagnosis of abnormal copper metabolism in liver diseases mainly involves genetic diseases that affect copper metabolism, such as gene defects of CDG-related disease, ABCB4 gene defect disease (progressive familial intrahepatic cholestasis type 3), Adaptor related protein complex 1 subunit sigma 1 (AP1S1) gene defect disease (MEDNIK syndrome) and SLC33A1 gene defect disease (Huppke-Brendl syndrome) (24).