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D. R. Hoffman, D. K. H. Wheaton, D. G. Birch; Docosahexaenoic Acid Profiles in Red Blood Cells of Patients With Retinal Degenerative Diseases. Invest. Ophthalmol. Vis. Sci. 2007;48(13):574.
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. The long-chain ω3 polyunsaturated fatty acid, docosahexaenoic acid (DHA; 22:6ω3) is an integral component of cell membranes throughout the body with particularly high levels in the retina and brain. About 25 years ago, blood fatty acid levels were first noted to be abnormal in patients with retinitis pigmentosa. Here we examine DHA levels in red blood cells (RBCs) as an index to the fatty acid status in patients with retinitis pigmentosa (RP), Stargardt macular degeneration (STGD), and allied retinal diseases including Leber Congenital Amaurosis (LCA), choroideremia (CHD), retinoschisis (RTS) and cone-rod dystrophy (CRD).
. Blood samples were collected by venipuncture from 185 healthy volunteers (range: 4-82y) and 478 patients with retinal disease referred for research studies by retinal specialists. To limit the dietary contribution of DHA, individuals consuming >3 fish meals per week or taking fish oil/ DHA supplements were excluded from analysis. Following lipid extraction, methyl esters of thirty fatty acids from RBCs were quantified by gas chromatography (data reported as % total fatty acids).
. In normally-sighted volunteers, the mean RBC-DHA levels were 3.88% with a 95% confidence interval of 0.13%. Patients with RP (n=356) including autosomal dominant, autosomal recessive, isolate, X-linked, and Ushers type I, II, & III had a mean 21% reduction from normal [3.1±0.9% (SD); p<0.0005]. Patients with either X-linked RP (n=120) or autosomal recessive RP (n=23) had the lowest mean RBC-DHA levels of 2.6±0.6% and 2.6±0.7%; both 33% below normal. Patients with STGD had 17% reductions in DHA (3.2±0.7%; p=0.003; n=18). Patients with LCA, CHD, RTS, or CRD had reductions in DHA of 14% (p=0.08; n=8), 20% (p=0.002; n=15), 26% (p<0.0005; n=14), and 20% (p<0.0005; n=33) compared to normals.
. The mechanism(s) responsible for reductions in blood DHA levels in patients with retinal diseases of varied genetic origins is unknown. Down-regulation of the DHA biosynthetic pathway has been demonstrated in patients with X-linked RP and may be under hormonal control (Hoffman et al. JLR 2001) or a retinal trigger (Scott & Bazan, PNAS 1989). Nutritional DHA supplementation by-passes in vivo DHA production resulting in an elevation of blood DHA levels. The potential for slowing inherited retinal disease progression in DHA intervention trials remains under active investigation.
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