GCH1 and diabetes mellitus: Furthermore, we showed that augmentation of cardiomyocyte BH4, by targeted cardiomyocyte over‐expression of Gch1, selectively increases cardiomyocyte BH4 levels and augments myocardial NOS activity leading to alterations in myocardial relaxation, and protection against cardiomyopathy induced by diabetes (Carnicer Hijazo et al., 2021).