ANO5-related muscle diseases: From clinics and genetics to pathology and research strategies

Anoctamin-5 (ANO5) is a multi-pass membrane protein localized to the sarcolemma and the sarcoplasmic reticulum. Mutations were linked to rare autosomal recessive muscle diseases. Here, we summarize the clinical spectrum, imaging data and molecular research findings as well as results of animal modeling, which significantly moved forward the understanding of mechanisms underlying ANO5-related muscle diseases. Given that precise histological information on inflammatory processes taking place in patient-derived muscle are still lacking, an (immuno)histological study on biopsies derived from six ANO5-patients was performed showing focal accumulation of necrotic fibers, mild fiber-size variances and myophagocytosis. In addition, MRI data of four ANO5-patients (including a 10-year follow-up in one patient) are presented and discussed in the context of previously published MRI-findings. Hence, data presented in this article combining a review of the literature with own myopathological findings address scientific trends and open questions on ANO5-related muscle diseases, which would be of significant interest for a wide neuromuscular diseases community. To conclude, a clear genotype–phenotype correlation does not exist, and ANO5-related muscle disorders might represent the next entity of a clinical continuum with varying degree of muscle cell pathologies. In addition, results of pre-clinical studies allowed the definition of suitable cell and animal models characterized by certain histological and functional pathologies resembling the human phenotype. These models might serve as suitable systems for testing of interventional concepts in future.