FKBP1B and hydrops fetalis: Other studies, measuring the FKBP12.6 that can be immunoprecipitated with the solubilised RyR2 complex, demonstrated a decrease in the FKBP12.6/RyR2 ratio of 50% (paced dog) or 65% (human HF) (Marx et al., 2000) or 38% (rabbit aortic insufficiency) (Ai et al., 2005).