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D.K. Wheaton, W.J. Kimberling, M.L. Jensen, M. Tuazon, B.D. Stier, D.R. Hoffman; Blood Docosahexaenoic Acid (DHA) Levels in Individuals With Genotypically–Defined Usher Syndrome . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4604.
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Deficiencies in the long–chain omega–3 polyunsaturated fatty acid, DHA, are associated with sub–optimal retinal, visual, and neurodevelopment. Patients with Usher syndrome, a genetic disease leading to loss of hearing and sight, are reported to have reduced blood DHA levels (Bazan et al., 1986; Anderson et al., 1998); however, previous studies have not genotypically characterized the patients. We conducted a study to analyze blood lipid profiles and assess differences in DHA levels among patients ascribed to one of the major genetically defined subtypes of Usher syndrome, namely, 1B, 1C, 1D, 1F, 2A, 2C and 3A.
Blood samples were collected from 124 individuals (14–80 yrs) affected with Usher syndrome for determination of red blood cell (RBC) fatty acid levels using capillary column gas chromatography. Dietary questionnaires were completed by each participant to document dietary intake of DHA–rich food sources and nutritional supplements. Individuals were excluded from data analysis if, 1) ingesting DHA or fish oil supplements (n=17); or 2) ingesting ≥4 cold water, oily fish meals (3 ounces each) per week with a RBC–eicosapentaenoic acid level >1% (n=6). Data from normal, age–matched controls (n=160; 14–71 yrs) meeting dietary inclusion criteria were used for fatty acid comparison (% of total fatty acids; mean±SD).
RBC–DHA was decreased by 11% compared to normal in the Usher syndrome cohort (n=101); 3.56±0.89% affected vs. 3.98±0.94% normal (p=0.0003). 67 patients were found to have mutations in one of the defined subtypes; specifically, type 1B (n=12), type 1C (n=1), type 1D (n=2), type 1F (n=1), type 2A (n=45), type 2C (n=3) and type 3A (n=3). RBC–DHA was reduced by 16% in type 1, by 9% in type 2, and by 8% in type 3; 3.35±0.98 (p=0.01), 3.63±0.98 (p=0.02) and 3.67±0.41 (p=0.0001), respectively.
Patients with Usher syndrome exhibit significantly decreased RBC–DHA levels. The type 1 sub–group is associated with a more severe phenotype and demonstrated the greatest reductions compared to normal. Understanding the differences in DHA status between the genetic types is crucial to the conception and design of a DHA nutritional intervention to delay the progression of retinal degeneration in these patients.
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