The initial steps in vision start with light detection by visual pigment located in the neural retina and recycling of the visual pigment in the adjacent retinal pigment epithelium (RPE). RPE65 is a critical enzyme in the recycling of 11-cis-retinal, a cofactor that is required for light-sensitivity in the retina. When RPE65 is mutated, it causes a severe childhood-onset blindness called Leber congenital amaurosis, type 2 (LCA2). The Rpe65 gene knockout (KO) mouse was developed for the study and treatment of LCA2 and resembles the human disease in many important ways, but the KO mouse has a large Rpe65 gene deletion and such mutations are rarely found in humans. New mouse models, tvrm148 and rd12, contain point mutations in the Rpe65 gene that are similar to, or identical to, mutations found in humans. I hypothesized that the tvrm148 or rd12 point mutations would result in visual phenotypes different from the KO. I found that the tvrm148 mutation in Rpe65 caused a loss in visual function that was virtually identical to the KO because of low levels of RPE65 protein that had no enzymatic activity. In contrast, the rd12 mutation caused a much faster loss of visual function compared to tvrm148 or KO mice and inherited in a semidominant fashion, unlike the KO and many typical LCA2 patients. These mice produced no detectable RPE65 protein and no RPE65 enzymatic activity. The rd12 mice accumulated mutant Rpe65 mRNA that inefficiently associated with ribosomes for translation, and I conclude this contributes to the unusually aggressive form of blindness. These findings supported my hypothesis that point mutations could produce visual defects that differed from the KO mutation. These findings are important because treatments being developed for the disease are based on work in the KO mouse, and my work suggests that these treatments may not be as effective for all human mutations. Furthermore, because the rd12 mutation is found in humans and because my findings showed that it produced a more aggressive blindness, I recommend these patients need to be monitored for an unusually aggressive form of LCA2 that might be more difficult to treat.
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