FKBP1B and hydrops fetalis: It has been proposed that in HF hyperphosphoryation by PKA of S2809 specifically causes the loss of the RyR2 modulatory protein FKBP12.6 (Yano et al., 2000) whereas CaMKII (Wehrens et al., 2004b) or PKC did not cause a similar dissociation (Marx et al., 2000; Wehrens et al., 2004b), although CaMKII is reported to phosphorylate S2809 (Witcher et al., 1991; Marx et al., 2000; Rodriguez et al., 2003).