*2.1. Definitions*

Left ventricular enlargement (LVE) was ascertained when the left ventricular end diastolic diameter (LVEDD) exceeded 112% of the predicted value, corrected for age and body surface area according to Henry's formula, while left ventricular dysfunction (LVD) was ascertained when left ventricular ejection fraction (LVEF) was <50%. The diagnosis of DCM was made when both criteria were met. When no LVE but more distinct LVD was present (LVEF < 45%), hypokinetic non-dilated cardiomyopathy (HNDC) was diagnosed [17]. In the presence of other relevant abnormalities, such as LVE > 117%, cardiac conduction defect (CCD), or atrial or ventricular arrhythmias unexplained by other conditions, we used the term indeterminate cardiomyopathy (indeterminate CM).

CCD included atrioventricular block (AVB) and left bundle branch block (LBBB). First-degree AVB was defined by a PR interval>200 ms on standard 12-lead ECG. High-degree AVB included type II second degree or third degree AVB. Atrial arrhythmias included atrial fibrillation, flutter, and paroxysmal tachycardia lasting ≥30 s. Non-sustained ventricular tachycardia (nsVT) was defined as ≥3 consecutive ventricular beats at >120 bpm and a duration for <30 s on 24-h Holter electrocardiographic monitoring. If the VT lasted over 30 s, it was considered sustained (sVT). Ventricular arrhythmias included sVT, nsVT, and frequent ventricular extrasystoles (>500/24 h).

HF was recognized in the presence of typical symptoms (e.g., breathlessness or fatigue), accompanied by structural and/or functional cardiac abnormalities, resulting in a reduced cardiac output and/or elevated intracardiac pressures. End-stage HF was defined as HTX, implantation of left ventricular assist device, or death caused by HF.

MVA was defined as sudden cardiac death (SCD), cardiopulmonary resuscitation (CPR), or appropriate implantable cardioverter defibrillator (ICD) shock (an ICD discharge for termination of ventricular fibrillation/VT). Death was classified as sudden if it occurred within 1 h of the onset of cardiac manifestations, during sleep (in the absence of previous hemodynamic deterioration), or within 24 h after the patient was last seen apparently stable clinically. Sudden cardiac arrest (SCA) was defined as occurring within 1 h of the onset of acute symptoms and was reversed by CPR. Relatives included all probands' family members with *LMNA* gene mutation confirmed as a result of cascade screening, irrespective of degree of kinship. A family history of SCD was considered positive if ≥1 first degree relative had died suddenly before the age of 60 years.
