A Swiss DSG2 Founder Variant Promotes Left Ventricular Thrombus Formation Causing Cardioembolic Stroke in Autosomal Recessive Arrhythmogenic Cardiomyopathy

Aims: Arrhythmogenic cardiomyopathy (ACM) is a genetic disease defined by arrhythmias and myocardial fibrosis with impaired cardiac function and increased risk of sudden cardiac death. Pathogenic variants are mostly identified in desmosomal genes such as desmoglein-2 (DSG2). We identified a novel disease phenotype in patients homozygous for the DSG2 variant c.523+2T>C (splice site of exon 5/intron 5), characterized by cardioembolic events in addition to classical ACM features. Here, we evaluate this new thromboembolic phenotype by comparing the clinical data to specific murine disease models. Methods and Results: We describe three unrelated patients presenting with an embolic event and/or left ventricular thrombus. Clinical evaluation revealed a shared right ventricular ACM phenotype characterized by arrhythmias, impaired function, and fibrotic remodeling. In addition, patients exhibited localized fibrotic changes of the left ventricular apex with formation of an aneurysm and predisposition to thrombus formation. Genetic analysis identified the DSG2 variant c.523+2T>C as a founder variant from the "Bernese Oberland". To elucidate the variant's functional impact, a mouse model deficient for Dsg2 exon 5 (Dsg2{Delta}ex5) was established and compared to a model carrying the adhesion-deficient Dsg2-W2A variant. Echocardiography, ECG, and histology in Dsg2{Delta}ex5 mice revealed similar disease patterns to patients and a loss of DSG2 expression. Importantly, these animals exhibited left apical fibrosis with aneurysm formation and left ventricular thrombus formation. In contrast, the Dsg2-W2A model presented with a biventricular ACM-phenotype but without left ventricular thrombi. Conclusions: We identified a novel ACM phenotype in patients homozygous for the DSG2 founder variant c.523+2T>C characterized by left ventricular apical fibrosis. Dsg2{Delta}ex5 mice recapitulate the patients' phenotype suggesting a causative link between left ventricular aneurysm due to DSG2 deficiency and thrombus formation with subsequent embolism. This highlights a novel pathological feature of ACM and the need for variant and phenotype-specific therapy.