PEX11B and peroxisomal disease: Notably, mutations in the PEX11 genes can lead to diseases in mammals: deficiency in PEX11β, one of the three mammalian paralogs of Pex11, causes neurological and developmental defects of the Zellweger syndrome spectrum in mice [12,13], and a mutation in PEX11β was found in a patient with symptoms somewhat atypical for peroxisome biogenesis disorders [14].