The vast allelic heterogeneity (more than 1000 disease-causing ABCA4 variants) makes genotype–phenotype correlations challenging.35 However, there is increasing evidence that onset relates to the severity of the underlying ABCA4 variants, with childhood-onset STGD being associated with more deleterious variants (including nonsense variants) compared with adult-onset or the later onset foveal-sparing STGD (more frequently missense variants). The gene discussed is ABCA4; the disease is severe early-childhood-onset retinal dystrophy.