ABCA4 Gene: Function, Mutations, and Associated Retinal Diseases

ABCA4 encodes the ATP-binding cassette transporter ABCA4 (also known as ABCR), predominantly expressed in retinal photoreceptor outer segments. It functions as a flippase for N-retinylidene-phosphatidylethanolamine (N-Ret-PE), facilitating the clearance of all-trans-retinal and preventing toxic bisretinoid accumulation. Loss-of-function mutations lead to lipofuscin deposition in retinal pigment epithelium, causing progressive vision loss. Over 1,000 pathogenic variants are associated with autosomal recessive Stargardt disease, cone-rod dystrophy, and retinitis pigmentosa.

Tissue Expression

Cell Line Expression

Hotspot Mutations

Mutation functional classification

• Retinoid cycle (visual cycle)

• ATP-binding cassette (ABC) transporters

• Phospholipid transport in photoreceptors

ABCA4 is a 2,273-amino acid transmembrane protein with two nucleotide-binding domains (NBDs) and two transmembrane domains (TMDs). It localizes to the rims of photoreceptor outer segment discs. The protein uses ATP hydrolysis to flip N-retinylidene-PE from the lumenal to the cytoplasmic leaflet, enabling all-trans-retinal reduction and recycling. Structural studies reveal a 'lumenal gate' that opens upon substrate binding. Mutations disrupting NBD ATPase or substrate recognition cause retinal degeneration.