This protein family, named Coiled-coil domain-containing protein 66 (CCDC) refers to a protein domain found in eukaryotes, and is approximately 160 amino acids in length. CCDC66 protein is detected mainly in the inner segments of photoreceptors in many vertebrates including mice and humans. It has been found in dogs, that a mutation in the CCDC66 gene causes generalized progressive retinal atrophy (gPRA). This shows that the protein encoded for by this gene is vital for healthy vision and guards against photoreceptor cell degeneration. The structure of CCDC66 proteins includes a heptad repeat pattern which contains at least one coiled-coil domain. There are at least two or more alpha-helices which form a cable-like structure.