Abstract 4147380: Cardiomyocyte Contractile Phenotype as a Marker of Cardiomyopathy Risk

Introduction: Cascade genetic screening for risk stratification is standard practice in the family of a patient diagnosed with hypertrophic cardiomyopathy (HCM), provided that a pathogenic mutation is present. We sought an alternative to genetic testing for cases where the patient lacks any suspicious variants (genotype-negative). Hypothesis: Induced pluripotent stem cell (iPSC)-derived cardiomyocytes from HCM patients with pathogenic mutations exhibit one or more altered contractile parameters when formed into engineered heart tissues (EHTs). These include elevated peak force, delayed relaxation, or blunted length-dependent activation (LDA). We hypothesized that EHTs derived from genotype-negative HCM patients would show similar contractile aberrations. If so, aberrant contractile phenotype could serve as a marker of HCM risk in screening family members when genetic testing is inconclusive. Methods: A total of 18 iPSC lines were obtained from a combination of public biobanks, institutional sources, and blood samples from consenting patients. These included lines from apparently healthy individuals (n=11) and from genotype-unknown or genotype-negative HCM patients (n=7). Four of the healthy lines were randomly selected as reference controls and the remaining 14 lines formed a blinded cohort. iPSCs were differentiated into cardiomyocytes and formed into EHTs using MyoPod tissue scaffolds. Following three weeks of culture, EHT contractility and LDA were assessed. Bootstrapping analysis was used to compare blinded EHT behavior against the reference group to mimic a diagnostic test. Results: None of the genotype-negative EHT groups showed statistically significant contractile differences compared to reference panels. One apparently healthy control EHT showed a significant (p<0.05) increase in contractile force; exome sequencing revealed a rare FHOD3 mutation (D284N). Only one HCM patient line showed statistically significant change in contractility relative to reference (31% drop in normalized LDA, p<0.05). Sequencing revealed a known pathogenic HCM mutation ( MYH7 K351E) in that patient. Conclusions: EHTs derived from genotype-negative HCM patients do not exhibit detectable alterations in contractile behavior, but patient EHTs harboring suspected or known pathogenic variants reliably do. This method has the potential to determine mutation penetrance in specific patients or pathogenicity of novel variants.