ABCA4 and cone-rod dystrophy: Consistent with the model that clinical phenotypes are dependent on the residual activity of ABCA4 protein (5, 6), variants resulting in null alleles, such as stop-gain, frameshift, canonical splice site, and large copy number variants, have been documented in the most severe phenotypes, such as cone-rod dystrophy, rapid-onset chorioretinopathy (ROC), and even generalized choriocapillaris dystrophies with retinitis pigmentosa–like features (6–10).