GPSM2 and Chudley-McCullough syndrome: The causal gene for Chudley-McCullough syndrome GPSM2, POC1B linked to a congenital form of cone-rod dystrophy, GRK1 associated with a congenital stationary night blindness are involved in photoreceptor functioning [169–171, 187, 188], while NYX causing a congenital form of stationary night blindness and LHX4 linked to congenital pituitary hormone deficiency are involved in the communication between photoreceptors and cone bipolar cells [87, 189–196].