Discovery cohort—study population and genetic analyses

The discovery cohort comprised 770 consecutively evaluated unrelated patients with HCM referred to the Inherited Cardiovascular Disease unit at St. Bartholomew’s Hospital, London, UK, and before 2015, to the Inherited Cardiovascular Disease Unit at The Heart Hospital, UCLH, London, UK. The samples used in this study were collected from 2013 to 2018. All patients gave written informed consent, and the study was approved by the regional ethics committee (15/LO/0549). Clinical evaluation was as previously described.15^,16 HCM was diagnosed according to current European Society of Cardiology guidelines.1 Patients with previously confirmed HCM phenocopies were excluded from the study.

DNA extraction, library preparation, whole-exome sequencing, variant calling, and annotation were performed as described previously16; variants identified with a minor allele frequency more than or equal to 0.0001 in the Genome Aggregation Database (gnomAD)17 (in any population) were removed from further analysis. The analysis of large rearrangements was performed using a read-depth strategy (ExomeDepth).18 Prioritized variants were confirmed by conventional automated (Sanger) DNA sequencing.16