ABCA4 and Stargardt disease: Functional impairment of the ABCA4 protein is responsible for a wide range of retinal degeneration phenotypes, including Stargardt disease 1 (STGD1), cone–rod dystrophy 3 (CRD3), retinitis pigmentosa 19 (RP19), and other conditions collectively referred to as ABCA4-associated retinopathies (Sheremet et al., 2018; Cremers et al., 2020).