Successful RPE65 gene replacement and improved visual function in humans

Leber congenital amaurosis (LCA) is a group of severe autosomal recessive retinal dystrophies unified by the onset of blindness at birth and absence of ERG signals. Mutations in fourteen genes are currently associated with LCA, accounting for approximately 60% of patients. LCA genes encode retinal proteins that participate in a variety of significant retinal pathways ranging from photoreceptor development to replenishing vitamin A in the retinoid cycle. In some of the genetic subtypes of LCA (e.g. RPE65), viable photoreceptors and a relatively intact retina have been discovered. Consequently, successful photoreceptor and visual rescue have been achieved in mice and canine models of LCA. Two research groups, one in Philadelphia, USA (Maguire et al.) another in London, England (Bainbridge et al.) recently tested RPE65 replacement in two human trials with a total of six LCA patients. Remarkably, visual improvements were documented by ETDRS visual acuity measurements, pupillometry, nystagmus frequency, visual field measures, perimetry and an obstacle course. There were no local, or systemic side effects, nor improvements in ERG measures. These spectacular results will now stimulate further investigations of younger patients, higher dosages, and clinically or genetically related retinal disorders.