[Ultrastructural changes of skeletal muscle tissue of patients with dysferlinopathy]

Dysferlinopathy represents an orphan disease within the spectrum of progressive muscular dystrophies, occurring at a frequency of 1 to 9 cases per 1.000.000 individuals (Orphanet, 2024). It arises from mutations in the DYSF gene (OMIM 603009, 2p13, NM_003494.4), which is responsible for coding the transmembrane protein dysferlin. Dysferlin plays a critical role in the repair of muscle fiber membranes and the cellular processes of skeletal muscle regeneration. Although the molecular mechanisms of dysferlin-mediated repair are under active investigation, reports on the ultrastructural alterations in human skeletal muscles due to dysferlin deficiency are sparse.

To identify the ultrastructural pathomorphological features of skeletal muscles in 6 patients with dysferlinopathy.

This study presents pathomorphological, immunohistochemical, and ultrastructural data from skeletal muscle biopsies of 6 patients with molecularly confirmed dysferlinopathy.

Examination of paraffin-embedded sections of the anterior tibialis and vastus lateralis muscles, stained with hematoxylin and eosin, identified a primarily myopathic pattern of skeletal muscle injury. Immunohistochemical staining with dysferlin antibodies revealed the absence of the protein in muscle tissue compared to the positive control. Transmission electron microscopy has revealed ultrastructural alterations characteristic of dysferlinopathy, although not specific, including thickening and fragmentation of the basal membrane, thinning and lysis of myofibrils, folding and disruptions of the sarcolemma, destruction of mitochondria, and, newly described in this disease, necrosis of myosatellite cells and telocytes in skeletal muscles.

Despite the non-specificity of the identified ultrastructural alterations, electron microscopy of skeletal muscle biopsies in dysferlinopathy can provide additional information about the mechanisms underlying the disease development. The finding of myosatellite cell and telocyte necrosis indicates the impairment of skeletal muscle regenerative capacity, which may be a novel link in the pathogenesis of dysferlinopathy.