Peroxisome biogenesis disorders (PBDs), thought to be inherited in an autosomal recessive manner, are caused by mutation in one of several PEX genes. Ahlemeyer et al. study the effects in mice of homozygous versus heterozygous deletion of Pex11b, which has a known role in peroxisome proliferation. Surprisingly, heterozygotes show signs of neuronal cell death, delayed neuronal differentiation and increased levels of oxidative stress, although to a lesser extent than homozygotes. These data suggest that mutation of a single Pex allele can cause neurological defects, and represent one of the first reports of oxidative stress being involved in the pathology of PBDs. Page 125

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