PDE4A and Schnyder corneal dystrophy: Six different PDE types (PDE1, PDE2A, PDE3B, PDE4, PDE5, and PDE9A) have been identified in RBCs to date and are important for the regulation of cAMP or cGMP (Almeida et al., 2008; Adderley et al., 2010; Adderley et al., 2011), however, their distinct roles in the regulation of RBC deformability in SCD are unknown.