There are four different forms of STGD (1–4) and three known disease genes.28,29 STGD1 is autosomal recessive and caused by mutations in the PR-specific ATP-binding cassette (ABC) transporter gene, ABCA4, which is a key protein of the visual cycle that transports N-retinylidene-phosphatidylethanolamine (N-ret-PE) to the cytosolic side of the PR disc membrane.30 Mutations in ABCA4 result in misfolded or dysfunctional proteins that lead to inefficient transportation of N-ret-PE and consequently N-ret-PE condensation. The gene discussed is ABCA4; the disease is severe early-childhood-onset retinal dystrophy.