**4. Channelopathies**/**Channel-Related Mutations**

Mutations that a ffect channel protein structure and function resulting in disease are termed channelopathies. Spontaneously occurring retinal channelopathies have been identified in dogs resulting from mutations in the cyclic nucleotide-gated ion channels (CNG) of the rod and cone photoreceptors and the anion channel bestrophin 1 (BEST1).

CNG channels in the rod and cone photoreceptors are directly involved in phototransduction. The CNG channels expressed in the rod photoreceptor consist of four subunits: three CNGA1 and one CNGB1 [72–74]. The CNG channel in cone photoreceptors consists of CNGA3 and CNGB3 proteins, in a 3:1 or 2:2 ratio (the stoichiometry of the CNGA3/CNGB3 channel is under debate) [72]. Damaging mutations in the rod CNG channels result in RP, while mutations in cone CNG channels result in achromatopsia.

BEST1 is a homopentameric channel expressed in the retinal pigment epithelium (RPE) and involved in anion transport and intracellular calcium homeostasis [75]. Mutations in *BEST1* result in a collection of retinal diseases. Mutations in *BEST1* often result in Best Vitelliform Macular Dystrophy, but the age of onset, mode of inheritance, disease characteristics and prognosis can vary [75].
