Using the gene-editing tool CRISPR/Cas9, researchers at University of California San Diego School of Medicine and Shiley Eye Institute at UC San Diego Health, with colleagues in China, have reprogrammed mutated rod photoreceptors to become functioning cone photoreceptors, reversing cellular degeneration and restoring visual function in two mouse models of retinitis pigmentosa. The findings are published in the April 21 advance online issue of Cell Research. Retinitis pigmentosa (RP) is a group of inherited vision disorders caused by numerous mutations in more than 60 genes. The mutations affect the eyes' photoreceptors, specialized cells in the retina that sense and convert light images into electrical signals sent to the brain. There are two types: rod cells that function for night vision and peripheral vision, and cone cells that provide central vision (visual acuity) and discern color. The human retina typically contains 120 million rod cells and 6 million cone cells. In RP, which affects approximately 100,000 Americans and 1 in 4,000 persons worldwide, rod-specific genetic mutations cause rod photoreceptor cells to dysfunction and degenerate over time. Initial symptoms are loss of peripheral and night vision, followed by diminished visual acuity and color perception as cone cells also begin to fail and die. There is no treatment for RP. The eventual result may be legal blindness. In their published research, a team led by senior author Kang Zhang, M.D., Ph.D., Chief of Ohthalmic Genetics, Founding Director of the Institute for Genomic Medicine and Co-Director of Biomaterials and Tissue Engineering at the Institute of Engineering in Medicine, both at UC San Diego School of Medicine, used CRISPR/Cas9 to deactivate a master switch gene called Nrl and a downstream transcription factor called Nr2e3.
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