Abstract 4362966: Patient-specific IPSC-derived Cardiomyocyte Phenotypes Reflect Clinical Variation Within a Family With FLNC Cardiomyopathy

Background: Truncating variants (TVs) in the filamin C gene ( FLNC ) have been associated with familial cardiomyopathies. However, phenotypes of individuals carrying the same variant exhibit variable penetrance in disease onset, rate of progression, and severity of arrhythmias and cardiomyopathy. Research Question: Can patient-specific, stem-cell-derived cardiomyocytes (iCMs) recapitulate differences in FLNC clinical phenotypes. Methods: A proband with severe dilated cardiomyopathy and a TV in FLNC (c.1844dup, p.Ile616Aspfs*4) was identified in a family where the FLNC variant and cardiac disease co-segregated with variable severity. To investigate differences in clinical penetrance and phenotype, we generated patient-specific induced pluripotent stem cell (iPSC) from the severely affected proband and the father with mild disease. iPSCs were differentiated into iCMs and were studied using multi-electrode array (MEA), immunofluorescence analyses (IFA), calcium indicators, and RNAseq for differential gene expression analyses (DGEA). Results: Compared to control iCMs, an increase in beat period irregularity and arrhythmogenicity was observed in both FLNC -iCMs. Proband iCMs showed more prominent changes in calcium dynamics, decreased field potential duration, and shortening of the action potential. Sarcomeric structure as seen in IFA of α-actinin and filamin C was more disorganization in the proband iCMs. Gene expression analysis revealed changes in pathways related to cardiac muscle contraction, electrophysiology, cell communication, and cardiac conduction of varying degrees corresponding to clinical severity of the patient derived iCMs. Confirmatory analysis using RNAseq was performed using CRISPR-knock-in of the FLNC TV into an isogenic iPSC line. Conclusions: Our results provide evidence that patient-specific iPSCs can provide mechanistic insights that reflect phenotypic differences between patients with the same cardiomyopathic FLNC pathogenic variant. DGEA identified common and unique pathway perturbations that may lead to specific therapeutic approaches.