PEX1 and peroxisome biogenesis disorder: Pathogenic variants in the PEX1 gene account for nearly 2/3 of all PBD-ZSD cases, and over a third of cases are caused by pathogenic variants in any of PEX6, PEX12, PEX26, PEX10, PEX2, PEX5, PEX13, PEX16, PEX3, PEX19, PEX14, and PEX11β (ordered from most frequent to least frequent genetic cause of ZSD) [4].