JAK1 and cardiac hypertrophy: Although the dilated cardiomyopathy phenotype observed with cardiomyocyte loss of JAK1 was not present in Myh6-Cre controls at 6 months of age (Fig. 4, Supplemental Table S2) nor was cardiac hypertrophy observed at the whole organ level at 8 months of age (Fig. 5B, Supplemental Fig. S3B) compared to Jak1fl/fl controls, we did observe an increase in cardiomyocyte size in Myh6-Cre hearts at 8 months of age, albeit not to the same extent as cardiomyocytes of Jak1-deleted hearts (Supplemental Fig. S3A, C–D).