Clinical Outcome of Hypertrophic Cardiomyopathy in Probands with the Founder Variant c.913_914del in MYBPC3: A Slovenian Cohort Study.

Hypertrophic cardiomyopathy is often caused by pathogenic MYBPC3 variants. The study of Italian patients with HCM and MYBPC3(NM_000256.3):c.913_914del showed a higher disease penetrance in males and a higher frequency of arrhythmias compared to patients with other likely pathogenic and pathogenic (LP/P) MYBPC3 variants. We investigated the clinical outcomes of Slovenian probands with MYBPC3 LP/P variants, estimated the variant penetrance and compared the results with an Italian study. We identified 31 haplotype-matched individuals with MYBPC3:c.913_914del and 34 individuals with other LP/P MYBPC3 variants. We observed some significant differences in clinical and echocardiographic characteristics and frequency of adverse cardiac events between Slovenian and Italian probands with MYBPC3:c913_914del. We were unable to replicate previous findings for MYBPC3:c.913_914del, highlighting the complexity of genotype-phenotype associations.

Non-dilated left ventricular cardiomyopathy with arrhythmias is commonly caused by the nonsense variant DSP:c.3793G>T in Slovenian patients.

DSP-cardiomyopathy has recently been recognised as a specific type of cardiomyopathy. Using an in-house Mendelian disease registry, we aimed to identify probands with likely pathogenic or pathogenic DSP variants. We detected these variants in 4.8% and 77.8% of genotype-positive probands referred for dilated and non-dilated left ventricular cardiomyopathy (NDLVC), respectively. We identified six Slovenian probands with the DSP:c.3793G>T and characterised them along with further eight of their relatives at the molecular and phenotypic level. Medical records revealed NDLVC with arrhythmia in six individuals (five probands, one relative; 33 ± 14 years; three males, three females). All had subepicardial late gadolinium enhancement on cardiac MRI (CMRI), and five received an ICD. Four individuals (one proband, three relatives; 48 ± 14 years; all female) had no ECG and/or cardiac abnormalities on CMRI detected. Our analysis presents a Slovenian-specific molecular pathology of DSP cardiomyopathy, delineates the clinical manifestation of DSP:c.3793C>T, and thereby improves the understanding of the clinical outcomes associated with truncating DSP variants.

A novel splice-site FHOD3 founder variant is a common cause of hypertrophic cardiomyopathy in the population of the Balkans-A cohort study.

Founder variants in sarcomere protein genes account for a significant proportion of disease-causing variants in patients with hypertrophic cardiomyopathy (HCM). However, information on founder variants in non-sarcomeric protein genes, such as FHOD3, which have only recently been associated with HCM, remains scarce. In this study, we conducted a retrospective analysis of exome sequencing data of 134 probands with HCM for recurrent pathogenic variants. We discovered a novel likely pathogenic variant c.1646+2T>C in FHOD3 in heterozygous state in eight probands with HCM and confirmed its presence in seven additional relatives. Individuals with this variant had a wide range of ages at onset of the disease (4-63 years). No adverse cardiac events were observed. Haplotype analysis revealed that the individuals with this variant shared a genomic region of approximately 5 Mbp surrounding the variant, confirming the founder effect of the variant. FHOD3 c.1646+2T>C is estimated to have arisen 58 generations ago (95% CI: 45-81) in a common ancestor living on the Balkans. A founder FHOD3 c.1646+2T>C variant is the second most common genetic variant in our cohort of patients with HCM, occurring in 16% of probands with a known genetic cause of HCM, which represents a substantially higher proportion than the currently estimated 0.5-2% for causal FHOD3 variants. Our study broadens the understanding of the genetic causes of HCM and may improve the diagnosis of this condition, particularly in patients from the Balkans.