Preface of Special Issue "Molecular Therapies for Inherited Retinal Diseases".

Inherited retinal diseases (IRDs) are a group of progressive disorders that lead to severe visual impairment or even complete blindness. IRDs display a vast heterogeneity, clinically as well as genetically, with over 250 genes identified in which mutations can cause one or more clinical subtypes of IRD. Long considered incurable diseases, intense research over the last two decades, combined with major technological advancements, have enabled the development of the first therapeutic approaches for these diseases. The approval of LuxturnaTM (voretigene neparvovec), a gene augmentation therapy vector for RPE65-associated IRD, by the US Food and Drug Administration and the European Medicines Agency, is considered a true milestone in the field, and has led to the development of similar, or different therapeutic strategies for many other subtypes of IRD. Despite these major achievements, there are still many aspects that can-and need to-be improved, including more insights into the relationship between genetic variation and cellular dysfunction, optimization of the vectors and sequences used, improving delivery methods, as well as understanding and modulating the (local) immune response. In addition, the extreme rarity of some genetic subtypes of IRDs poses an enormous challenge on the development of novel therapies, in terms of e.g., costs and regulatory affairs.[...].