In humans, mutations causing dysfunction in PEX1, PEX6, and PEX26—the human equivalents to yeast Pex1, Pex6, and Pex15—are the most prevalent cause of rare genetic disorders called peroxisome biogenesis disorders (PBDs) [19]. The gene discussed is PEX1; the disease is Peroxisome biogenesis disorder-Zellweger syndrome spectrum.