Calpainopathy (limb-girdle muscular dystrophy type R1): clinical features, diagnostic approaches, and...

Calpainopathy, or limb-girdle muscular dystrophy type R1/2A (LGMDR1/2A), is the most prevalent form of LGMD, comprising about 32% of all cases. The disease is caused by mutations in the CAPN3 gene, leading to dysfunction of the corresponding protein-an enzyme critical for muscle fiber cytoskeleton remodeling and protein signaling regulation through selective proteolysis. Clinical manifestations demonstrate significant phenotypic polymorphisms, ranging from oligosymptomatic forms to severe early-onset cases, with the loss of ambulation occurring 10-25 years after disease onset. A characteristic feature is predominantly symmetrical involvement of limb and trunk muscles, leading to early mobility loss, disability, and reduced work capacity. Noninvasive imaging can suggest dystrophic muscle disease but requires differentiation from other myopathies. Confirming the diagnosis involves histological, immunological, and molecular genetic studies to identify calpain-3 activity or CAPN3 gene expression alterations. Currently, no targeted or etiological therapies are available for calpainopathy. Treatment focuses on symptom management, complication prevention, and slowing disease progression. Preclinical research demands the development of an appropriate animal model that displays disease phenotypes mirroring those observed in humans. Preclinical and clinical research are also investigating therapeutic options, including the use of drugs that have proven effective in other myopathies and genome editing via transgenic CAPN3 delivery to restore protein activity. Gene therapy has shown promise in murine models, but safety concerns, particularly systemic toxicity affecting the heart and other organs, remain significant. This review comprehensively analyzes the clinical features, diagnostic approaches, and advancements in modeling and therapeutic development for calpainopathy.