*2.1. Clinical Description of Studied Patients and of Their Families*

Comprehensive clinical, laboratory, and electrophysiological data of all index cases were collected. Two probands of them (P2, P4) also underwent cardiovascular magnetic resonance imaging (Siemens Trio scanner, Siemens Medical Solutions, Erlangen, Germany) as described previously [17]. All available relatives undertook cardiologic screening, which included physical examination, electrocardiography, and echocardiography as well as a collection of blood samples for genetic analysis. Patients with suspected disease-causing *DES* variants were subjected to a detailed neurologic assessment, measurement of serum creatine phosphokinase, nerve conductance, and electromyography of two muscles (left vastus medialis and left deltoid muscle), as reported previously [17].

The study was approved by the Institutional Review Board´s representing all clinical collaborators (Institute for Clinical and Experimental Medicine and Thomayer´s Hospital; 1st Faculty of Medicine of the Charles University and General Faculty Hospital; both Prague) and was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all probands.
