Autoimmune myositis （AIM） is a group of autoimmune diseases that primarily affect muscle fibers， often accompanied by the involvement of multiple organs such as the skin，lungs，and joints.It is the most common treatable skeletal muscle disease in adults. Although most patients with AIM can achieve remission with traditional immunosuppressive therapies， their quality of life can be heavily reduced due to drug-related adverse effects and the high relapse rate and high disability rate of the disease. With the deepening understanding of the immunopathological mechanisms of AIM，various biologics targeting different components of these mechanisms have brought new hope for patients with AIM. This article reviews the advances in the treatment of AIM.

Glycogen storage disease type Ⅱ （GSD Ⅱ）， also known as Pompe disease， is a common autosomal recessive lysosomal storage disease with predominantly muscle tissue involvement， and it is caused by defects in the GAA gene which encode acid α-D-glucosidase in lysosomes. According to the age of onset and the main organs involved， it is classified into infant-onset Pompe disease （IOPD） and late-onset Pompe disease（LOPD）. The diagnosis of this disease depends on the reduction in GAA enzyme activity， the detection of GAA gene mutations， and muscle tissue biopsy， and early diagnosis and treatment are crucial for prognosis. Recombinant human GAA（rhGAA） enzyme replacement therapy prepared by the gene recombination technology is currently the main disease-modifying treatment method for Pompe disease， among which the earliest drug alglucosidase α has shown good efficacy in improving muscle strength and respiratory function and prolonging survival time， and the new-generation rhGAA drugs avalglucosidase α and cipaglucosidase alfa provide new options， especially for patients with poor outcomes and severe symptoms. Substrate ablation therapy and gene therapy are still under exploration， and disease-modifying therapies combined with nutritional and exercise therapies and multidisciplinary long-term management will achieve twice the result with half the effort.
Diagnosis

Sporadic late-onset nemaline myopathy （SLONM） is a rare， acquired， and treatable myopathy with a subacute or chronic progressive clinical course， characterized by asymmetric muscle atrophy and weakness in the axial and limb muscles， with or without involvement of respiratory and cardiac muscles. The only definitive diagnostic method at present is the identification of rods accumulation in muscle fibers by muscle biopsy pathology. This article provides a review of the clinical manifestations， diagnostic evaluations， muscle pathology， and advances in the treatment of SLONM.
Immunotherapy

Lipid storage myopathy （LSM） is a lipid metabolic disorder characterized by excessive lipid droplet accumulation in muscle fibers. Classic multiple Acyl-CoA dehydrogenase deficiency （MADD）， also known as glutaric aciduria type Ⅱ， is a disease with various clinical manifestations caused by mutations in electron transfer flavoprotein （ETF） and ETF-ubiquinone oxidoreductase. In recent years， a large amount of evidence has shown that classic late-onset MADD caused by mutations in the electron transfer flavoprotein dehydrogenase gene is the main cause of LSM. Besides classic MADD， many other diseases with similar changes in blood acylcarnitines and urinary organic acids can also cause LSM， and such diseases are call MADD-like disorders or MADD spectrum. This article reviews the clinical， pathological， biochemical， and molecular features of LSM with various etiologies and the latest advances in treatment， with a focus on the latest findings associated with MADD spectrum.
Riboflavin

Mitochondrial diseases are a group of hereditary disorders characterized by impaired oxidative phosphorylation in the mitochondrial respiratory chain caused by defects in either mitochondrial DNA or nuclear DNA， and such diseases have complex and diverse clinical manifestations and often involve multiple organs and systems， with the main manifestation of lesions in the nervous system and muscles due to their high energy demands. At present， there is still a lack of effective therapies for most mitochondrial diseases， and therefore， multidisciplinary management is essential in clinical practice， integrating various therapeutic approaches to provide personalized treatment regimens for patients with mitochondrial diseases. The primary treatment principle involves the timely correction of pathological and physiological abnormalities through pharmacological interventions， dietary modifications， and exercise management， along with the prompt treatment of system-specific impairments and the prevention of potential complications.
Diagnosis

Deep intronic variants refer to genetic variants located within intronic regions that are more than 100 base pairs away from exon-intron boundaries. These variants have historically been overlooked in the genetic testing of hereditary skeletal muscle diseases. Conventional genetic testing methods, such as whole exome sequencing, primarily focus on coding regions and exon-intron junctions [±(50-200) bp], thereby failing to detect abnormalities in extensive intronic regions. Furthermore, assessing the pathogenicity of identified deep intronic variants remains challenging. Recent studies have demonstrated that certain hereditary myopathies can be attributed to deep intronic variants. The underlying pathogenic mechanisms include the formation of pseudoexons, activation of cryptic splice sites, and disruption of transcriptional regulation. Although deep intronic variants can be detected using whole-genome sequencing or third-generation long-read sequencing technologies, these approaches are associated with high costs and difficulties in interpreting the results. Clinically, a combination of multiple detection methods is necessary for comprehensive analysis. Integrating functional validation techniques, such as RNA sequencing and minigene assays, facilitates the interpretation of deep intronic variants and enhances diagnostic yield, thereby offering novel insights into the diagnosis and management of hereditary myopathies.

Systemic amyloidosis is a disease caused by the deposition of misfolded proteins that often affects multiple organs, including the heart and kidneys, etc . Amyloid myopathy is one of the manifestations, but it has been considered rare. However, recent studies have found amyloid deposition in skeletal muscle even in patients with neither muscle weakness nor creatine kinase elevation, suggesting that skeletal muscle involvement may be underestimated. At present,"amyloid myopathy" lacks clear diagnostic criteria, and amyloid deposition in skeletal muscle does not always accompany myopathy symptoms, so "skeletal muscle amyloidosis" may be a more appropriate diagnosis. The exact mechanism of muscle injury caused by amyloid deposition in skeletal muscle is not clear, and may be involved in the scope of amyloid involvement, amyloidosis peripheral neuropathy, and immune activation.