KCNJ8 and Cowden syndrome 1: Remarkably, analogous to CS patients (Brownstein et al., 2013; Cooper et al., 2014; Levin et al., 2016), heterozygous kcnj8+/V65M KI larvae showed significantly elevated mean end-diastolic (mEDV) and end-systolic (mESV) volumes with strikingly enhanced cardiac output (53%) (Fig. 2B) due to equally increased stroke volume (P<0.0001) at 5 days post-fertilization (dpf) (Fig. S7).