GYS1 and glycogen storage disease II: Recent studies employing a double genetic knockout of Gys1 and GAA demonstrate characteristics of glycogen accumulation in a model of Pompe disease, cardiomegaly and type II muscle fiber atrophy, can be abrogated by knocking out Gys1. 30 In the same study, it was shown that Gys1/GAA double knockouts had better tetanic force generation and fatigue resistance compared to GAA knockout animals.