PTPN21 and retinal degeneration: In conclusion, while the two genes, SPATA7 and PTPN21 are expressed in canine retina, especially cone and rod photoreceptors, our studies clearly demonstrate that the deficiency in SPATA7 and not PTPN21 is responsible for the early onset Day Blindness/Retinal Degeneration phenotype present in SP that models the LCA and cone-rod dystrophy phenotype reported in some patients [37,39,50].