ABCA4 and Stargardt disease: One example supporting our theory is that mutations in the photoreceptor-specific gene ABCA4 impair the visual cycle and cause accumulation of abnormal toxic retinoid in the RPE, which in turn leads to Stargardt’s macular dystrophy.35 Similar to our cases, primary defects of photoreceptors leading to secondary RPE/choriocapillaris impairments were also revealed in mice overexpressing mutated PRPH2 p.R172W, another photoreceptor-specific gene associated with CACD.29 This PRPH2 mutation led to dominant defects in cones followed by loss of integrity of the RPE and choriocapillaris.