2.1
Inherited retinal dystrophies (IRDs) are a group of rare genetic eye diseases. They are caused by germline mutations in more than 260 genes, including that for the enzyme RPE65. This enzyme is critical for the visual cycle. It is involved in a multistep process that converts light entering the eye into electrical signals, which are transmitted to the brain. Lack of RPE65 causes severe deficiency in functional rhodopsin (a sensory protein that converts light into an electrical signal) and death of photoreceptor cells on the retina through accumulation of toxic chemical compounds. People with RPE65-mediated IRD have progressive vision loss. There is variation in the presentation and time of diagnosis of the condition. Loss of vision can begin as early as the first few months of life, or during childhood or adolescence. Initially, people have problems with peripheral vision and seeing in dim light or night blindness. These symptoms are followed by progressive deterioration in visual field (range of vision) and visual acuity (clarity of vision), and reduced sensitivity to light. Ultimately, the deterioration leads to near-total blindness.