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 asso ciated with fatty acid abnormalities within cell membrane phospholipid s, red blood cell membrane (RBC) phosphatidylethanolamine (PE) fatty a cid content (% of total fatty acids) was measured using high performan ce liquid chromatography and capillary column gas chromatography in 15 5 patients from separate families with different genetic types of RP a nd 101 normal subjects. After controlling for the effects of age and s ex, 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) c ontent, and significantly (P < 0.001) elevated mean RBC PE dimethyl ac etal (DMA) forms of 16:0, 18:0, and 18:1 omega 9 (n-9) as compared wit h normal subjects. RBC PE content of 22:5 omega 3 (n-3) (a precursor t o 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 domi nant, recessive, X-linked, and isolate forms of RP. The relative amoun ts of plasmalogens as indicated by DMA forms of 16:0 and 18:0 were sig nificantly (P < 0.01) increased in dominant (by 33% and 25%), recessiv e (by 36% and 25%), and isolate cases (by 32% and 26%) of RP as compar ed with normal subjects. No such differences were seen in X-linked cas es versus controls. Our data indicate that RBC PE DHA content is decre ased in all genetic types of RP patients as compared to control subjec ts, and that RBC PE plasmalogens art increased in dominant, recessive, and isolate forms of RP. These data raise the possibility that membra ne phospholipid fatty acid abnormalities may contribute to the pathoge nesis of RP.