Restrictive Physiology Associated with an MYH7 Mutation in the Absence of Hypertrophy: A Multimodality Imaging Case Report

The mutation in the Myosin Heavy Chain 7 (MYH7) gene, which encodes the β-myosin heavy chain, is one of the most common and clinically significant genetic abnormalities associated with cardiomyopathy. While it is most frequently linked to hypertrophic cardiomyopathy, recent studies have increasingly linked MYH7 mutations to certain forms of restrictive cardiomyopathy (RCM) as well. Case Presentation: We present the case of a 25-year-old patient without personal or family history of cardiovascular disease. The patient was admitted with symptoms of fatigue, exertional dyspnea, and a transient loss of consciousness. Electrocardiogram revealed bradycardia and repolarization abnormalities. Echocardiography showed normal left ventricular volumes and ejection fraction, severely dilated left atrium, and restrictive LV filling pattern. Cardiac magnetic resonance imaging (CMR) showed preserved systolic function, evidence of interstitial fibrosis, and marked left atrial dilation. Subsequent genetic testing revealed a pathogenic MYH7 variant and a likely pathogenic ABCC9 variant, supporting the diagnosis of a genetically determined cardiomyopathy with restrictive features. This case highlights the importance of integrating advanced imaging and genetic testing in patients with unexplained restrictive physiology and preserved systolic function, even in the absence of myocardial hypertrophy.