Autosomal recessive Stargardt disease is caused by mutations in the ABCA4 gene. Mutations in ABCA4 are also found in two-thirds of cases with autosomal recessive cone-rod dystrophy, and a small fraction of patients with autosomal recessive retinitis pigmentosa. Patients with autosomal recessive retinitis pigmentosa, the most severe of these three phenotypes, invariably carry ABCA4 inactivating mutations; patients with autosomal recessive cone-rod dystrophy and Stargardt disease carry combinations of mutations that do not completely inactivate the retina specific 'ATP-binding cassette transporter' (ABCR) protein. DNA diagnostics is complicated by the high allelic heterogeneity and the uncertainty as to whether some ABCA4 variants are pathological. Nevertheless, ABCA4 mutation analysis is particularly important for patients with cone-rod dystrophy to confirm the autosomal recessive mode of inheritance.