SCN4A and chronic obstructive pulmonary disease: A study reported that SCN4A variants caused cardiac arrhythmias and Brugada syndrome (29), and a German study found that six MC patients with CLCN1 variants had cardiac arrhythmias or conduction defects, and three of them had pacemaker implanted (4), but the type and severity of cardiac abnormalities observed in the different studies (including the present study) were very heterogeneous.