RHO and retinitis pigmentosa 1: Over 200 causative genes have been identified, but the most common is rhodopsin, which is responsible for 40% of all known cases of RP.[1–3] In particular, the P23H mutation of rhodopsin is the most common cause of autosomal dominant retinitis pigmentosa (ADRP) in North America, as it is responsible for 12% of all known cases.[3–5] In this form of RP, the mutant rhodopsin is misfolded, which may lead to endoplasmic reticulum stress and, ultimately, rod cell death (for review see [6]).