KCNH2 and mucopolysaccharidosis: To validate the drug response of the cardiac MPS we tested two pharmacological agents, Isoproterenol (β-adrenergic agonist) and E-4031 (hERG blocker), and two clinically used drugs with known clinical effects, Verapamil (multi-ion channel blocker) and Metoprolol (β-adrenergic antagonist) (Table 1).