PEX1 and peroxisome biogenesis disorder: Approximately 60% of PBD-ZSD patients have bi-allelic mutations in the PEX1 gene of whom 40% are compound heterozygous or homozygous for the missense mutation c.2528G>A, which results in a p.G843D amino acid change causing impaired PEX1 protein function (Ebberink et al., 2011).