Supplementary Material for: Genetic Spectrum of Left Ventricular Non-Compaction in Paediatric Patients

<b><i>Introduction:</i></b> Left ventricular non-compaction (LVNC) represents a genetically heterogeneous cardiomyopathy which occurs in both children and adults. Its genetic spectrum overlaps with other types of cardiomyopathy. However, LVNC phenotypes in different age groups can have distinct genetic aetiologies. The aim of the study was to decipher the genetic spectrum of LVNC presented in childhood. <b><i>Patient Group and Methods:</i></b> Twenty patients under the age of 18 years diagnosed with LVNC were enrolled in the study. Target sequencing and whole-exome sequencing were performed using a panel of 108 cardiomyopathy-associated genes. Pathogenic, likely pathogenic, and variants of unknown significance found in genes highly expressed in cardiomyocytes were considered as variants of interest for further analysis. <b><i>Results:</i></b> The median age at presentation was 8.0 (0.1–17) years, with 6 patients presenting before 1 year of age. Twelve (60%) patients demonstrated reduced ejection fraction. Right ventricular (RV) dilation was registered in 6 (30%), often in combination with reduced RV contractility (25%). Almost half (45%) of the patients demonstrated biventricular involvement already at disease presentation. For pathogenic and likely pathogenic variants, the positive genotyping rate was 45%, and these variants were found mainly in non-contractile structural sarcomeric genes (<i>ACTN2</i>, <i>MYPN</i>, and <i>TTN</i>) or in metabolic and signal transduction genes (<i>BRAF</i> and <i>TAZ</i>). Likely pathogenic <i>TAZ</i> variants were detected in all 5 patients suspected of having Barth syndrome. No pathogenic or likely pathogenic variants were found in genes encoding for sarcomeric contractile proteins, but variants of unknown significance were detected in 3 out of 20 patients (<i>MYH6</i>, <i>MYH7</i>, and <i>MYLK2</i>). In 4 patients, variants of unknown significance in ion-channel genes were detected. <b><i>Conclusion:</i></b> We detected a low burden of contractile sarcomeric variants in LVNC patients presenting below the age of 18 years, with the major number of variants residing in non-contractile structural sarcomeric genes. The identification of the variants in ion-channel and related genes not previously associated with LVNC in paediatric patients requires further examination of their functional role.