Gene Therapy with RPGR Gene Preserves Vision in Canine RPGR X-Linked Retinitis Pigmentosa, Even at Later Stages of Blinding Disease After Significant Loss of Photoreceptor Cells

Gene therapy preserved vision in a study involving dogs with naturally occurring, late-stage retinitis pigmentosa, according to research funded by the National Eye Institute (NEI), part of the National Institutes of Health. The findings contribute to the groundwork needed to move gene therapy forward into clinical trials for people with this blinding eye disorder, for which there is currently no cure. Scientists from the University of Pennsylvania and the University of Florida, Gainesville, also determined, for the first time, that gene therapy may be of potential benefit even after there has been significant loss of cells in the eye. Up to this point, animal studies had shown benefits from gene therapy only when it was used in the earliest stages of the disease. "The study shows that a corrective gene can stop the loss of photoreceptors in the retina, and provides good proof of concept for gene therapy at the intermediate stage of the disease, thus widening the therapeutic window," said Neeraj Agarwal, Ph.D., a program director at the NEI. Retinitis pigmentosa is one of the most common inherited diseases that causes degeneration of the retina, the light-sensitive tissue lining the back of the eye. Roughly 1 in 4,000 people are affected and about 10 to 20 percent have a particularly severe form called X-linked retinitis pigmentosa, which predominately affects males, causing night blindness by age 10 and progressive loss of the visual field by age 45. Approximately 70 percent of people with the X-linked form carry mutations that cause loss of function of the retinitis pigmentosa GTPase regulator (RPGR) gene, which encodes a protein important for maintaining the health of photoreceptors. These are cells in the retina that absorb and convert light into electrical signals, which are then sent to the brain.
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