Refsum's disease: nature of the enzyme defect

Two siblings with Refsum's disease, an inherited disorder of lipid metabolism, oxidized intravenously injected uniformly labeled phytanic acid-C(14) at rates less than 5 percent of those found in normal subjects. The defect in oxidation of phytanic acid persisted in cultures of fibroblasts from the patients' skin. The rate of oxidation of the phytanic acid-C(14) was less than 1 percent of that found in cultures of fibroblasts from normal skin. However, pristanic acid, previously shown to be the first product of phytanic acid degradation, was oxidized at a normal rate in the patients' cultures. These results indicate that the enzymatic defect in Refsum's disease is in the first step of the pathway for degradation of phytanic acid, that is, in the unusual alpha-oxidative process that leads to a shortening of phytanic acid by one carbon atom.