ABCA4 and severe early-childhood-onset retinal dystrophy: Although administration of oversize AAV vectors achieves therapeutically-relevant levels of transgene expression in rodent and canine models of human inherited diseases (Allocca et al, 2008; Monahan et al, 2010; Grose et al, 2012; Lopes et al, 2013), including the retina of the Abca4−/− and shaker 1 ( sh1) mouse models of STGD and USH1B (Allocca et al, 2008; Lopes et al, 2013), the mechanism underlying oversize AAV-mediated transduction remains elusive.