Objective: To determine whether adipose and red blood cell membrane lipids,particularly long-chain polyunsaturated fatty acids such as docosahexaenoic acid and eicosapentaenoic acid,are significantly correlated with phenotype in a family with autosomal dominant Stargardt macular dystrophy (gene locus STGD3). Amutation in the ELOVL4 gene is responsible for the macular dystrophy in this family,and its disease-causing mechanism may be its possible involvement in fatty acid elongation in the retina. Methods: The subjects in this study included 18 adult family members known to have a 2-base pair deletion in the ELOVL4 gene. Control subjects included 26 family members without the mutation. Each subject received a complete eye examination including fundus photographs,the results of which were used to grade the severity of macular dystrophy on a 3-tier scale. Red blood cell membrane and adipose tissue lipids were analyzed as an indication of short-term and long-term dietary fatty acid intake. Results: When adipose lipids were analyzed,there was a significant inverse relationship between phenotypic severity and the level of eicosapentaenoic acid (r=-0.54; P =.04). When red blood cell lipids were analyzed,there were significant inverse relationships between phenotypic severity and levels of eicosapentaenoic acid (r=-0.55; P=.02) and docosahexaenoic acid (r=-0.48; P=.04). Conclusions: These results indicate that the phenotypic diversity in this family may be related to differences in dietary fat intake as reflected by adipose and red blood cell lipids. Clinical Relevance: This study demonstrates that dietary factors can influence the severity of an inherited human macular dystrophy. Objective: To determine whether adipose and red blood cell membrane lipids, particularly long-chain polyunsaturated fatty acids such as docosahexaenoic acid and eicosapentaenoic acid, are highly correlated with phenotype in a family with autosomal dominant Stargardt macular dystrophy (gene locus STGD3). Amutation in the ELOVL4 gene is responsible for the macular dystrophy in this family, and its disease-causing mechanism may be its possible involvement in fatty acid elongation in the retina. Methods: The subjects in this study included 18 adult family members known to have a 2- base pair deletion in the ELOVL4 gene. Control subjects included 26 family members without the mutation. Each subject received a complete eye examination including fundus photographs, the results of which were used to grade the severity of macular dystrophy on a 3-tier scale. Red blood cell membrane and adipose tissue lipids were analyzed as an indication of short-term and long-term dietary fatty acid intake. Results: When adipose lipids were analyzed, there was a significant inverse relationship between phenotypic severity and the level of eicosapentaenoic acid (r = -0.54; P = .04). When red blood cell lipids were analyzed, there were significant inverse relationships between phenotypic severity and levels of eicosapentaenoic acid (r = -0.55; P = .02) and docosahexaenoic acid (r = -0.48; P = .04). Conclusions: These results indicate that the phenotypic diversity in this family may be related to differences in dietary fat intake as reflected by adipose and red blood cell lipids. Clinical Relevance: This study demonstrates that dietary factors can can the severity of an inherited human macular dystrophy.