Background: Different cardiomyopathies like dilated, restrictive or arrhythmogenic cardiomyopathy, can be caused by missense or small in-frame mutations in the DES gene. This gene encodes the muscle specific intermediate filament (IF) protein desmin, which is the major component of the cardiac IFs. The cardiac IFs connect the Z-bands, desmosomes, costameres and different cell organelles like mitochondria and nuclei. Therefore, desmin is important for the structural integrity of cardiomyocytes. However, the significance of most reported DES missense mutations remains currently unknown since functional data are lacking in most cases.

Material and Methods: A set of 34 different variants with unknown significance (VUS) localized in the 1A desmin subdomain, which are listed in the ClinVar and HGMD databases, was generated. Induced pluripotent stem cells (iPSCs) were differentiated into cardiomyocytes by modulation of the Wnt-pathway. iPSC-derived cardiomyocytes were transfected with different desmin expression constructs and we analyzed systematically the desmin filament assembly by cell transfection experiments in combination with confocal microscopy.

Results: Missense mutations at the N-terminus of the desmin 1A coil subdomain cause abnormal cytoplasmic desmin aggregation whereas most of the C-terminal VUS have no detectable affect on the filament assembly.

Conclusion: In our study we investigated systematically all reported VUS localized in the 1A-subdomain of the DES gene. By doing this, we identified a genetic hotspot in the DES gene, which may have relevance for classification of cardiomyopathy associated genetic variants. In addition, our study might be important for risk prediction in the genetic counselling of affected cardiomyopathy patients carrying DES mutations.