GNAT2 and achromatopsia: Accounting for the estimated prevalence of the known underlying genetic causes of ACHM (40%–50% CNGB3; 20%–30% CNGA3; < 2% GNAT2,5PDE6C, and PDE6H),6,7 it is estimated that the genetic cause of at least 15% of ACHM cases remains unknown (although some of these cases may represent missed intronic variants or even misdiagnosed BCM);8 thus, there is a need to develop methods to better differentiate these conditions clinically.