A genotype–phenotype correlation model was proposed to explain the wide range of phenotypes associated with biallelic pathogenic variants in ABCA4. This genotype–phenotype correlation model links the residual activity of the ABCA4 protein to the severity of retinal dystrophy (van Driel et al., 1998; Maugeri et al., 1999). This evidence concerns the gene ABCA4 and inherited retinal dystrophy.