The use of multiple gRNAs can increase the amount of gene knockdown (Tsai et al., 2018), but over-suppression may also be detrimental as VEGF is required for the normal, physiologic maintenance of vascular and neural tissues (Kurihara et al., 2012), and chronic anti-VEGF treatments have been linked to geographic or choroidal atrophy in patients with AMD and DME (Yiu et al., 2014; Grunwald et al., 2015). The gene discussed is VEGFA; the disease is age-related macular degeneration.