Functional Characterization of a Novel Genetic Variant in Desmin (p.Glu353dup) Causing Myofibrillar Myopathy and Generation of Patient-Derived Induced Pluripotent Stem Cells for Disease Modeling
Desmin (DES) is a major intermediate filament protein crucial for the structural integrity and function of striated muscles. Mutations in DES have been associated with various forms of myopathies collectively known as "desminopathy." In this study, we identified a novel heterozygous mutation (c.1059_1061dupGGA) in exon 6 of DES in an Argentine family with myofibrillar myopathy. This mutation leads to the duplication of a glutamic acid residue at position 353 (p.Glu353dup) of the DES protein. Clinical and myo-pathological evaluations of the index patient revealed characteristic features of myofibrillar myopathy, including muscle weakness, atrophy, and muscle fatty replacement. In-silico analyses of DES dimer assembly revealed alterations in the coiled-coil structure and a more stable complex conformation when one or both monomers contain the mutation. Moreover, DES and vimentin (VIM) protein aggregates were observed in the membrane of HEK cells only when DES_dupGGA was overexpressed and not when wild-type DES was overexpressed. Both results suggest that p.Glu353dup mutation impairs the formation of a normal DES network after affecting its polymerization. To further investigate the disease mechanisms, patient-derived induced pluripotent stem cells (iPSCs) were generated from the index patient, his siblings, and a CRISPR-edited DES_dupGGA homozygous variant derived from the index patient iPSCs. Characterization of these iPSCs demonstrated normal pluripotency, karyotype and the ability to differentiate into cell types representing the three germ layers. In summary, our study contributes to the understanding of the molecular basis of myofibrillar myopathy caused by a novel DES mutation. The combination of clinical, molecular, and iPSC-based approaches offers insights into the pathogenesis of desminopathies and opens new possibilities for therapeutic development and precision medicine strategies.