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LCA is a severe retinal dystrophy characterised by an onset of symptoms before the age of 6 months, visual acuity below 201/400, searching nystagmus, sluggish pupillary reactions and no detectable responses on electrography. The visual fields are usually not measurable. LCA is genetically heterogeneous and is usually inherited in an autosomal recessive fashion. Seven genes have been reported to be mutated in LCA patients (AIPL1, CRB1, CRX, GUCY2D, RDH12, RPE65 and RPGRIP1). Each gene is responsible for a fraction of LCA patients. Mutations in these seven genes are estimated to underlie approximately 40-50% of LCA cases. Molecular genetic research is crucial to unravel the remaining genetic causes of this disabling disease.

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.