Background

Desmin (DES) is a muscle-specific intermediate filament protein that links the contractile apparatus to the cardiomyocyte cytoskeleton, organelles, and the nucleus. Genetic variants in the DES gene are a well-described cause for dilated cardiomyopathy (DCM). The molecular understanding of DES missense variants is incomplete.

Method

We analyzed a 7-years-old girl with chronic myocarditis and a DCM phenotype, her consanguine parents and two younger siblings using whole-exome sequencing (WES). The WES data were filtered for rare (minor allele frequency <10^-4) pathogenic genetic defects in cardiomyopathy disorder genes (n=89). Endomyocardial biopsy (EMB) samples were analyzed histologically, by immunohistology, and viral DNA/RNA real-time PCR. The identified DES missense variant was cloned into mammalian expression vectors and subsequently analyzed after transient overexpression. Imaging of intermediate filaments was performed after immunostaining with confocal microscopy. Differential mRNA splicing was tested using endpoint PCR in EMB.

Results

The female patient was first admitted with symptoms of severe heart failure, a left ventricular enddiastolic diameter of 51 mm, and a left ventricular ejection fraction (LVEF) of 33%. NT-proBNP level was elevated with 4205 ng/l and Troponin Ihs with 367 pg/nl. CMR detected no edema, but late gadolinium enhancement suggested myocardial fibrosis. In EMB chronic myocarditis was diagnosed without cardiac virus detection. The patient finally required a left ventricular assist device (LVAD) and heart transplantation. WES and filtering of variants in CMP disease genes identified a rare, pathogenic missense variant in DES (c.1244G>A, p.Arg415Gln) in homozygous state. This genetic variant implicates primary, genetically caused DCM. Immunostaining of DES in EMB revealed diminished protein levels in all analyzed EMB. The variant c.1244G>A alters a DES splice site but we did not identify altered differential splicing in mRNA isolated from patient EMB. Analysis of the DES p.Arg415Gln mutant protein revealed DES filament aggregation in human induced pluripotent stem cells derived cardiomyocytes.

Conclusion

The DES missense variant p.Arg415Gln underlies myocarditis and a phenotype of DCM. This report supports the idea that primary genetic defects inducing DCM may associate with chronic myocarditis. Moreover, missense variants in DES induce mutant protein aggregation leading to a dysfunctional cytoskeleton and DCM.

Keywords: desmin, genetic variants, dilated cardiomyopathy, myocarditis