Pathogenic truncating filamin C mutations presenting as acute myocarditis: a case series with insights from cardiac magnetic resonance and histological analysis.

Background: The exact mechanisms underlying the pathogenesis of myocarditis are not always understood, but there is emerging evidence to suggest that genetic factors may play a significant role. Case summary: Herein, we present six cases in which clinical, biochemical, and cardiovascular magnetic resonance data were consistent with myocarditis, and genetic testing subsequently revealed pathogenic filamin C (FLNC) mutations. Three patients presented with ventricular arrhythmias, two with severe biventricular dysfunction, and two suffered sudden cardiac arrest. Three received an implantable cardioverter defibrillator, and one underwent heart transplantation. Cascade testing was useful in identifying other relatives with FLNC mutation. We also present relevant histology results of myocardial specimens showing the presence of lymphocytic infiltration and inflammation, further supporting the potential association between FLNC mutations and a myocarditis phenotype. Discussion: Genetic testing of affected individuals for FLNC mutations and cascade screening in the setting of acute myocarditis may be considered in selected clinical context, such as in acute myocarditis accompanied by severe left ventricular systolic dysfunction, biventricular failure, significant ventricular arrhythmias, or right ventricular involvement.