Outside the Zellweger spectrum, adult Refsum disease has similar symptoms to infantile Refsum disease, but the adult-onset disease is due to a mutation in the PHYH gene that codes for the peroxisomal enzyme phytanoyl-CoA dioxygenase, which peroxisomes use to break down phytanic acid into pristanic acid (Wanders et al., 2011; Wanders and Poll-The, 2017; Gettelfinger and Dahl, 2018). This evidence concerns the gene PHYH and Refsum disease.