GCA and cardiomyopathy: Enhanced cardiomyocyte proliferation in the first 2 weeks of life was found in both Prkag2 cardiomyopathy, in which an adenosine monophosphate (AMP)-activated protein kinase mutation causes abnormal glycogen storage (Kim et al., 2014), as well as in mice with a deletion of guanylyl cyclase A (GC-A) that proceed to develop cardiac hypertrophy (Schipke et al., 2015).