MESP1 and hydrops fetalis: Cibi et al. (2020) have reported the development of hypertrophic cardiomyopathy in 2 mouse strains with a cardiac-null mutation of Prdm16 (Prdm16flox/flox; Mesp1-Cre and Prdm16flox/flox; αMHCMerCreMer/+), resulting in HF [13].