CD63 and retinal degeneration: The Tetraspanin (TSP) family is a crucial component of the tetraspanin-enriched membrane microdomain (TEM) superfamily, comprising 4 main subfamilies: the CD family (CD9, CD81 and CD151), the slow retinal degeneration (RDS) family (RDS-ROM), the uroplakin family (UPK1A/1B) and the CD63 family (CD63 and TSPAN31).