COL4A5 and catecholaminergic polymorphic ventricular tachycardia: The demonstration of depressed SERCA function, leaky RyRs and increased NCX activity helps us understand the hitherto unexplained phenotypic overlap between ATS1 and CPVT in some patients and the arrhythmias and intermittent paralysis seen in ATS1 and several other skeletal muscle diseases42–44.