ABCA4 and severe early-childhood-onset retinal dystrophy: This is perhaps best exemplified by disease‐causing variants in ABCA4, where those associated with childhood‐onset autosomal recessive Stargardt disease (STGD1) usually function as null alleles and are rare, while those associated with late‐onset STGD1 are often hypomorphic, have a greater prevalence in the general population, and so are less readily identifiable using current bioinformatics analysis (Fujinami et al., 2015).