Phytanic Acid Oxidase Activity in Cultured Skin Fibroblasts. Diagnostic Usefulness and Limitations

Patients with Refsum's disease lack the ability to degrade phytanic acid to pristanic acid and CO2. This defect is expressed in fibroblasts from the patients. An assay system for the degradation of phytanic acid in cultured skin fibroblasts is described. The assay makes it possible to single out patients with Refsum's disease from the cob-web of clinically related conditions. The sensitivity is, however, not good enough to diagnose the heterozygous state. A defect of the same pronounced degree as in Refsum's disease is also found in fibroblasts from patients with Zellweger's syndrome, neonatal adrenoleukodystrophy, and infantile Refsum's disease. The radioactive material remaining in the cells after incubation was identified as unmetabolized phytanic acid. No traces of radioactive intermediates could be found in the cells from any of the patient groups. This might indicate that the defects both in Refsum's disease and in the peroxisomal disorders are located either at the same metabolic step or at steps which are closely linked to each other.