Red blood cell membrane phosphatidylethanolamine fatty acid content in various forms of retinitis pigmentosa.

In order to test the hypothesis that retinitis pigmentosa (RP) is associated with fatty acid abnormalities within cell membrane phospholipids, red blood cell membrane (RBC) phosphatidylethanolamine (PE) fatty acid content (% of total fatty acids) was measured using high performance liquid chromatography and capillary column gas chromatography in 155 patients from separate families with different genetic types of RP and 101 normal subjects. After controlling for the effects of age and sex, patients with all genetic forms of RP had significantly (P < 0.001) reduced mean RBC PE 22:6 omega 3 (n-3) (docosahexaenoic acid, DHA) content, and significantly (P < 0.001) elevated mean RBC PE dimethyl acetal (DMA) forms of 16:0, 18:0, and 18:1 omega 9 (n-9) as compared with normal subjects. RBC PE content of 22:5 omega 3 (n-3) (a precursor to DHA) and 18:2 omega 6 (n-6) (the major dietary essential fatty acid) were not significantly different in RP than in controls. Analysis by genetic types of RP showed that the mean RBC PE DHA percentages were significantly reduced by 24%, 14%, 30%, and 17%, respectively, in dominant, recessive, X-linked, and isolate forms of RP. The relative amounts of plasmalogens as indicated by DMA forms of 16:0 and 18:0 were significantly (P < 0.01) increased in dominant (by 33% and 25%), recessive (by 36% and 25%), and isolate cases (by 32% and 26%) of RP as compared with normal subjects. No such differences were seen in X-linked cases versus controls. Our data indicate that RBC PE DHA content is decreased in all genetic types of RP patients as compared to control subjects, and that RBC PE plasmalogens are increased in dominant, recessive, and isolate forms of RP. These data raise the possibility that membrane phospholipid fatty acid abnormalities may contribute to the pathogenesis of RP.