Objective: The aim of this study was to explore the rare variants in a cohort of Romanian patients with hyper-trophic cardiomyopathy (HCM).

Methods: Twenty unrelated index patients with HCM were studied. The diagnosis of HCM was established according to the European Society of Cardiology (ESC) criteria. Targeted sequencing was performed on an Illumina MiSeq platform using TruSight Cardio Sequencing Kit (Illumina) following the manufacturer’s instructions. The procedure targeted 47 core and emer-ging genes associated with HCM and allowed a depth of coverage of minimum 20x for 99% of the target re-gions. An initial amount of 50 ng of proband DNA was used for optimal enrichment. For variant calling was employed GATK and Variant Call Format (VCF) files were produced as output. VCF files were processed with VariantStudio v3.0 software (Illumina).

Results: We identified 65 heterozygous mutations with allele frequency (AF)<1% in population databases. Forty mutations were nonsynonymous. Over 80% of the identified rare mutations were single nucleotide va-riants (n=54), while the indels were only 17%. Of note, one third of the rare variants (n=22) were singletons (AF=0 in Exome Aggregation Consortium database); also, 2 doubletons were identified (AF=0.000008 and 0.00008, respectively).

Conclusions: Herein we reported for the first time a number of rare variants in sarcomeric and non-sarco-meric genes related to HCM. The clinical significance of individual variants is yet to be established. Discri-minating between a pathogenic variant and a rare va-riant with no clinical significance is extremely challen-ging, especially in case of private mutations, which are unique for a family. Further family segregation analysis and functional studies are necessary for an accurate classification.