PEX7 and Usher syndrome: Together with these retinal developmental factors, myosin (MYO7A, synonym: USH1B, the cause of Usher syndrome)23, 24, transducin α (GNAT2, the cause of Achromatopsia)25, and peroxisomal targeting signal 2 receptor protein (PEX7, the cause of Refsum disease)26 are also known components of the CCT machinery27, 28, 29.