*4.1. Penetrance of Cardiolaminopathy Indicators*

A major finding of the study is that the earliest marker of the carrier status in *LMNA*-related cardiomyopathy is elevated hsTnT level, followed by widely recognized features, such as AVB, HF, and MVA [9,10,30]. In 2013, Rapezzi et al. [31] proposed a framework for the clinical approach to diagnosis in cardiomyopathies based on the recognition of diagnostic "red flags" that can be used to guide rational selection of specialized tests. Our study shows that elevated hsTnT level > 14 ng/L was present in two thirds of probands and in more than one third of relatives, indicating that it might be a "red flag" to introduce at least lifestyle modifications in asymptomatic or mildly symptomatic carriers. To the best of our knowledge, circulating cardiac biomarkers in relation to the disease penetrance or prognosis have not been reported in cardiolaminopathies. The role of circulating cardiac biomarkers in the detection of HF has been established [32]. Little is known about the significance of circulating biomarkers in early stage of DCM in humans [33], while routinely used biomarkers (NT-proBNP and hsTnT) are widely accepted in the diagnosis of occult DCM in Doberman Pinschers [34].

In the study, similarly to others, we found high and age-dependent penetrance of cardiac manifestations in *LMNA* mutation carriers [10,21,30]. Despite the fact that our study group was young (mean age at baseline was 33.2 years for all carriers and 29.0 years for the relatives), the majority of relatives (56%) had indeterminate CM and phenotypic expression was absent in only 31% of them. In the study by Kumar et al. [10], 18/35 (51.4%) relatives were phenotypically normal while the study cohort was older than the one we studied (mean age of 41 years). In the study by Pasotti et al. [21], 29/67 (43%) relatives had no signs of cardiomyopathy. This discrepancy may be related to adopted definitions of early stage disease but may also underscore the need of diagnostic vigilance (e.g., repeated 24-h ECG examinations). Of note, the Cardiomyopathy Registry of the EURObservational Research Programme of the European Society of Cardiology [35] showed that Holter monitoring was performed only in 37% of DCM patients. In the setting of cardiolaminopathies, it is of crucial importance to monitor asymptomatic carriers with Holter monitoring; however, the appearance of elevated hsTnT concentrations precedes the appearance of arrhythmia, as shown in our study.
