Omega-3 fatty acid status in patients diagnosed with Usher syndrome: a descriptive study of red blood cell (RBC) docosahexaenoic acid (DHA) levels in Usher subtypes
Usher syndrome is a genetic disease that includes visual impairment, due to progressive retinal degeneration, as well as congenital hearing loss. Night blindness is frequently the first ocular symptom and can occur within the first decade of life. Severe tunnel vision will typically lead to legal blindness by the second or third decade. Reduced blood levels of the long-chain omega-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA) have been reported in patients with Usher syndrome. DHA is found at its highest concentration in the human body in rod and cone photoreceptors suggesting a potential functional role in the phototransduction process of vision. Numerous studies have found defects in retinal and visual function of both animal models and humans deficient in omega-3 fatty acids including DHA. The current study used a retrospective, cross-sectional design to assess if blood levels of DHA (RBC-DHA) in patients with Usher syndrome were significantly different from normal. A secondary purpose was to determine if differences in RBC-DHA were evident between clinical and genotypic subgroups of Usher syndrome. The relationship between dietary intake and blood fatty acid status was explored and compared between the normal and Usher study cohorts.
Study participants were comprised of a convenience sample of normal controls (n = 60) and patients with Usher syndrome (n = 114) recruited from multi-state and nationwide patient registries. The present study demonstrated that the Usher syndrome cohort had lower mean RBC-DHA levels compared to normal (3.70% vs. 4.09%; p = .017). However, significant differences were not observed in DHA levels between clinical or genotypic subgroups. Calculated daily dietary DHA intake was not significantly different between the normal and Usher cohorts. Significant relationships were observed between DHA intake and RBC-DHA levels among both the normal and Usher cohorts (r = .470 and r = .433, respectively; p < .001). This study represents the first comprehensive comparison of blood DHA levels between each of the Usher clinical and genotypically-defined subtypes. These results contribute to our understanding of the omega-3 fatty acid status among patients with Usher syndrome and the association of dietary intake of DHA from omega-3 rich food sources.