GNAT2 and achromatopsia: Thus far, six genes have been implicated in achromatopsia-associated mutations [11–15]: cyclic nucleotide-gated channel alpha-3 (Cnga3) [16,17], cyclic nucleotide-gated channel beta-3 (Cngb3) [18,19], guanine nucleotide binding protein alpha transduction active peptide 2 (Gnat2) [1,20], phosphodiesterase 6C (Pde6c) [21,22], Pde6h [12,13], and cyclic AMP-dependent activating transcription factor-6 alpha (Atf6) [14,15].