GUCY2D and Rod-cone dystrophy: Particular GCAP1 mutants that weaken Ca2+ binding to GCAP1 (Dell’orco et al., 2010) cause constitutive activation of RetGC1 that directly leads to retinal degenerative diseases known as rod-cone dystrophies (Semple-Rowland et al., 1996; Sokal et al., 1998; Baehr and Palczewski, 2007; Behnen et al., 2010; Bondarenko et al., 2010; Jiang and Baehr, 2010; Dell’orco et al., 2014).