Project Summary/Abstract Retinitis pigmentosa (RP) is a heterogeneous group of disorders that cause retinal degeneration. To date, mutations in more than 58 genes have been linked to classic retinitis pigmentosa, and collectively all forms of inherited retinal dystrophies involves at least 300 genes. My studies are focused on retinitis pigmentosa-59 (RP59), a non-syndromic autosomal recessive form of RP caused by mutations in the dehydrodolichyl diphosphate synthase (DHDDS) gene, localized to exon 3 on chromosome 1p36.11. The most prevalent mutation is K42E, while T206A and R98W also have been reported. We generated a murine Dhdds K42E knock- in mouse model using CRISPR/Cas9 gene editing technology. Preliminary data shows significant reduction of ERG b-wave amplitudes and we have reported marked GFAP up-regulation, without retinal degeneration or decreased protein N-glycosylation. This suggests that defective DHDDS-dependent retinal degeneration may be more complicated than simply a loss-of-function mechanism due to altered protein glycosylation. To better understand the basis for selective retinal pathology associated with RP59 mutations, we plan to characterize the DhddsK42E/K42E knock-in mouse anatomically and physiologically. Additionally, we will create and analyze two new models of DHDDS-related inherited retinal disease, Dhdds T206A/T206A and DhddsT206A/K42E. Studying the retina in these mouse models will give us insight into the pathophysiology of this inherited disorder, and may lead to novel treatment options for this disorder.