Nonetheless, other specific genes may be investigated in case of suspicion of a systemic disorder such as glycogen storage disease (PRKAG2), Danon disease (LAMP2), Fabry disease (GLA), transthyretin amyloid cardiomyopathy (TTR), and Pompe disease (GAA), for which an early diagnosis could modify therapeutic options. The gene discussed is PRKAG2; the disease is Danon disease.