Unique Genetic Profiles in Hypertrophic Cardiomyopathy Patients From São Miguel Island (Azores, Portugal)

To investigate the clinical features and mutational spectrum underlying hypertrophic cardiomyopathy (HCM) in São Miguel Island (Azores, Portugal), we analyzed 37 adult patients (12 sporadic, 25 familial) with positive genetic tests. Seven disease-causing variants were identified, being two novels, in three sarcomeric genes (MYH7, TNNT2, and MYBPC3) and one non-sarcomeric gene (ALPK3). The novel variants, classified as likely pathogenic (LP), involved large multi-exon deletions in MYBPC3 (exons 26-32 and 28-33). These deletions were found in heterozygosity in two young males who remained clinically stable, though early onset may predict a more severe prognosis. Segregation analysis in a consanguineous family revealed two new genotypes: a digenic heterozygous for MYH7:c.1750G>C (p.Gly584Arg; P) and TNNT2:c.842A>T (p.Asn281Ile; LP) variants, and a homozygous for the TNNT2 variant. The 70-year-old homozygous patient remained stable and without arrhythmic events, challenging the belief that homozygous variants have a worse prognosis. This study is the first molecular and clinical analysis of HCM in the Azores.