In this report, functional studies on fibroblasts from ZSD patients carrying the PEX13 p.Arg294Trp variant (either in the compound heterozygous or the homozygous state) revealed a reduced number of PEX13 expressing, enlarged peroxisomes as well as a mitochondria mislocalization, that was triggered under particular cellular stress condition. The gene discussed is PEX13; the disease is peroxisome biogenesis disorder.