Genetic treatment for autosomal dominant inherited retinal dystrophies: approaches, challenges and targeted genotypes

Inherited retinal diseases (IRDs) have been in the front line of gene therapy development for the last decade, providing a useful platform to test novel therapeutic approaches. More than 40 clinical trials have been completed or are ongoing, tackling autosomal recessive and X-linked conditions, mostly through adeno-associated viral vector delivery of a normal copy of the disease-causing gene. However, only recently has autosomal dominant (ad) disease been targeted, with the commencement of a trial for rhodopsin ( RHO )-associated retinitis pigmentosa (RP), implementing antisense oligonucleotide (AON) therapy, with promising preliminary results ( NCT04123626 ). Autosomal dominant RP represents 15%–25% of all RP, with RHO accounting for 20%–30% of these cases. Autosomal dominant macular and cone-rod dystrophies (MD/CORD) correspond to approximately 7.5% of all IRDs, and approximately 35% of all MD/CORD cases, with the main causative gene being BEST1 . Autosomal dominant IRDs are not only less frequent than recessive, but also tend to be less severe and have later onset; for example, an individual with RHO -adRP would typically become severely visually impaired at an age 2–3 times older than in X-linked RPGR -RP. Gain-of-function and dominant negative aetiologies are frequently seen in the prevalent adRP genes RHO , RP1 and PRPF31 among others, which would not be effectively addressed by gene supplementation alone and need creative, novel approaches. Zinc fingers, RNA interference, AON, translational read-through therapy, and gene editing by clustered regularly interspaced short palindromic repeats/Cas are some of the strategies that are currently under investigation and will be discussed here.