New insight in lipid storage myopathy.

Lipid storage myopathy (LSM) is a lipid metabolic disorder characterized by the excessive accumulation of lipid droplets within muscle fibers. Classic multiple acyl-CoA dehydrogenase deficiency (MADD), also known as glutaric aciduria type II (GAII), is a clinically heterogeneous group of disorders caused by mutations in the electron transfer flavoprotein (ETF) and ETF-ubiquinone oxidoreductase (ETFQO). Growing evidence suggests that late-onset classic MADD due to ETFQO mutations is a primary cause of LSM. In addition to classic MADD, MADD-like disorders have also been identified as contributing factors to LSM, as supported by numerous studies. This review summarizes recent advances in the clinical, pathological, biochemical, and molecular features, as well as treatment outcomes, of LSM with various etiologies, with a particular focus on the latest findings regarding MADD-like disorders.