Microtubule-binding protein required for ciliogenesis. May function in ciliogenesis by mediating the transport of proteins like BBS4 to the cilium, but also through the organization of the centriolar satellites (By similarity). Plays a role in retina morphogenesis and/or homeostasis (PubMed:19777273). Homodimer; disulfide-linked (By similarity). Interacts with CEP290 (By similarity). Interacts with PCM1 (By similarity). Interacts with ARMC9, TOGARAM1, CSPP1 and CEP104 (By similarity). Restricted to the centrosomes and the spindle microtubules during mitosis (By similarity). Enriched in the inner segment of the photoreceptor (PubMed:19777273). Expressed in retina and blood (PubMed:19777273). Expressed in retina, mainly in photoreceptors but also in outer plexiform and ganglion cell layers (at protein level) (PubMed:19777273). Defects in CCDC66 are the cause of generalized progressive retinal atrophy (gPRA), characterized by continuous degeneration of photoreceptor cells leading to night blindness and progressive vision loss. A homozygous mutation in the CCDC66 gene resulting in a frameshift and the production of a truncated protein is probably causing the disease.