PDE6C and achromatopsia: Thus far, mutations in five genes have been identified to cause achromatopsia; they encode key components of the cone phototransduction cascade: the alpha (PDE6C) and gamma (PDE6H) subunits of cone cyclic guanosine monophosphate (cGMP) phosphodiesterase [2,3], the alpha subunit of cone transducin (GNAT2) [4,5], as well as the alpha (CNGA3) and beta (CNGB3) subunits of cone cyclic-nucleotide gated channel [6-8].