Gene therapy encompasses multiple techniques, including gene replacement, gene editing and gene silencing, with treatment choice dependent on whether the associated sequence variant(s) leads to a loss or gain in function.97 Human treatment trials of gene replacement therapy are already under way for retinal disease associated with mutations in ABCA4 (ClinicalTrials.gov identifier: NCT01367444) and RPGR (NCT03252847, NCT03116113 and NCT03316560), with results keenly awaited. The gene discussed is RPGR; the disease is Abnormal retinal morphology.