A randomized, placebo-controlled clinical trial of docosahexaenoic acid supplementation for X-linked retinitis pigmentosa

Abstract

Purpose Low docosahexaenoic acid (DHA) in X-linked retinitis pigmentosa (XLRP) may influence retinal function. The goals of this study were to elevate blood DHA levels and determine the effect on the rate of disease progression. Design In a 4-year prospective randomized clinical trial, male patients with XLRP (mean age = 16 years; range = 4–38 years) received DHA (400 mg/d; n = 23; +DHA group) or placebo (n = 21) capsules. Methods Red blood cell (RBC)-DHA concentrations were assessed every 6 months. Full-field cone electroretinograms (ERGs; the primary outcome measure), visual acuity, dark-adaptation, visual fields, rod ERGs, and fundus photos were recorded annually. Results In the +DHA group, RBC-DHA increased 2.5-fold over placebo levels (70 vs 28 mg DHA/l). Repeated measures analysis of variance for cone ERG showed a significant main effect of year ( P < .0001) but not of group ( P = .16). Preservation of cone ERG function correlated with RBC-DHA ( P = .018), and there was less change in fundus appearance in the +DHA group ( P = .04). Neither visual acuity nor visual fields were changed. In subset analysis, DHA supplementation was beneficial in reducing rod ERG functional loss in patients aged <12 years ( P = .040) and preserving cone ERG function in patients ≥12 years ( P = .038). Conclusions Although DHA-supplemented patients had significantly elevated mean RBC-DHA levels, the rate of cone ERG functional loss was not significantly different between groups. Supplemental analyses provided evidence for a DHA benefit and a direction for subsequent investigations.