Phytanic acid storage disease (Refsum’s disease) has presumably been included in the present Symposium under the rubric “...and Allied Disorders.” In that it is an inherited lipidosis and, like so many of them, affects the nervous system, it is to that extent “allied”. However, the differences are several and important. First, phytanic acid storage disease is due to a defect in an oxidative enzyme system, not a hydrolase; second, it is a disease in which a particular fatty acid accumulates (and in essentially all lipid classes), rather than a particular subclass of lipids as in the hydrolase deficiencies; and, finally, the accumulated lipid is of exogenous rather than endogenous origin. This last difference is especially important since it affords in theory the opportunity to arrest (and possibly reverse) the storage and to determine whether that alters the progression of the disease. Methods are being actively sought to do this in the sphingolipidoses, as reported elsewhere in this Symposium, but the approaches are difficult and results remain equivocal. Thus, it may be of interest to report in some detail our encouraging experience with dietary treatment of phytanic acid storage disease. First, let us briefly review the biochemical basis of phytanate accumulation, add some recent results on the normal pathway for its oxidation and then finally summarize the clinical responses to diet observed to date.
