Phenotypic Variability in Fraternal Twins with PEX1 Mutations: Zellweger Syndrome with Discordant Clinical Phenotype

Perioxisomal biogenesis disorders are a group of genetically and clinically variable disorders affect very-long chain fatty acid metabolism. Many PEX genes have been implicated in various disorders of the Zellweger syndrome spectrum (ZSS). Here we report the cases of fraternal twins who share the same PEX1 mutations and biochemical abnormalities classic ZSS, but who have a discordant clinical presentation. While twin A had classical clinical features of Zellweger Syndrome (ZS), twin B’s neonatal presentation was much milder and she may not have been initially identified as having ZSS had it not been for her brother’s presentation. The twins had nearly identical biochemical markers of peroxisome function. This report highlights the wide spectrum of ZSS and suggests that its variability cannot be accounted for by genetics, biochemistry, or even intrauterine environment.