PBDs, including Zellweger spectrum disorders (ZSDs), rhizomelic chondrodysplasia punctata type 1 (RCDP1) (Braverman et al, 1997; Motley et al, 1997; Purdue et al, 1997), and RCDP5 (Barøy et al, 2015), are caused by mutations of PEX genes encoding peroxins required for peroxisome assembly (Waterham & Ebberink, 2012; Fujiki et al, 2014; Fujiki, 2016). The gene discussed is PEX5; the disease is rhizomelic chondrodysplasia punctata type 1.