USH2A and Abnormal retinal morphology: Adeno-associated virus (AAV) vectors have been the gene transfer system of choice for human gene therapy, including retinal diseases.73, 74 However, a major limitation is that ABCA4 is larger than the current AAV vector capacity, a challenge that needs to be addressed for other genes that commonly cause inherited retinal disease, including USH2A.75 Subretinal injection of a lentivirus vector delivering ABCA4 has therefore been developed, given the larger cargo capacity of lentiviruses, and is currently in an ongoing Phase I/II clinical trial (ClinicalTrials.gov Identifier: NCT01367444).