RPE65 and retinal degeneration: When administered at an early stage of disease, protection against retinal degeneration results in sustained benefit in mice and dogs.4, 7 In humans, gene-augmentation therapy for RPE65 deficiency using AAV2/2 vectors can improve aspects of sight.8, 9, 10, 11, 12 However, improvements in photoreceptor function in humans have been relatively modest compared with those in animal models, even when retinal degeneration is relatively mild.