Peroxins are proteins involved in peroxisome biogenesis The peroxisome biogenesis factor Peroxin 2 (also designated Pex2) is an integral membrane protein of peroxisomes. Defects in the PXMP3 gene encoding Peroxin 2 are the cause of Zellweger syndrome-1 (ZWS-1), an autosomal recessive disorder due to defective import mechanisms for peroxisomal matrix enzymes. ZWS-1 is a severe form of the peroxisome-biogenesis disorders, a group of genetically heterogeneous, lethal diseases that are characterized by neuronal, hepatic and renal abnormalities, mental retardation and, in their most severe form, death within the first year of life.