Familial severe non-ischemic dilated cardiomyopathy with coexisting likely pathogenic BAG3 and FLNC variants: a case report

Background Dilated cardiomyopathy (DCM) is genetically heterogeneous. In severe non-ischemic DCM with familial clustering of heart-failure deaths, genetic testing and pedigree analysis may clarify etiology and guide cascade screening. Case presentation A 40-year-old woman presented with progressive dyspnea, chest tightness, and palpitations after an upper respiratory tract infection. Echocardiography showed severe left ventricular systolic dysfunction [left ventricular ejection fraction (LVEF) approximately 20%], left atrial enlargement, functional mitral regurgitation, and a small pericardial effusion. Serial cardiac troponin I and myocardial enzyme measurements remained within the reference ranges. Coronary angiography excluded obstructive coronary disease. Cardiovascular magnetic resonance (CMR) demonstrated global left ventricular hypokinesis and a clinically reported non-ischemic late-gadolinium-enhancement pattern at the papillary-muscle level involving the anterior/lateral wall. Because cardiac biomarkers remained normal and dedicated inflammatory CMR sequences were not acquired, active myocarditis could not be confirmed. Guideline-directed therapy reduced NT-proBNP from 4154 to 828 pg/mL, although angiotensin receptor-neprilysin inhibitor therapy was limited by symptomatic hypotension. At 2 months, symptoms and daily activity tolerance improved, but LVEF remained 25%, QTc was 479 ms, and ventricular premature complexes persisted. Whole-exome sequencing identified heterozygous likely pathogenic variants in BAG3 (NM_004281.4:c.180 + 1G > T) and FLNC [NM_001458.5:c.761_779del, p.(Leu254Profs*14)]. The daughter carried the BAG3 variant, whereas both children were negative for FLNC. The proband reported heart-failure-related deaths in her father and younger brother during adulthood and in a nephew during childhood. Conclusions The findings support complex familial non-ischemic DCM with marked variable expressivity. Coexisting BAG3 and FLNC variants should be interpreted as hypothesis-generating rather than proof of dual-gene causality. The infection-associated acute decompensation, persistently normal cardiac injury biomarkers, non-ischemic LGE, and incomplete inflammatory CMR characterization favor cautious interpretation rather than a definitive diagnosis of myocarditis. Serial imaging, rhythm surveillance, individualized device-risk assessment, and follow-up of genotype-positive relatives are essential.