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RESEARCH PRODUCT

Protein Aggregation in Muscle Fibers and Respective Neuromuscular Disorders

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Protein aggregation in muscle fibers may be a nonspecific phenomenon such as occurring in cores or ragged red fibers. However, it may also be a disease-specific and disease-significant phenomenon constituting protein aggregate myopathies (PAMs). These may be divided into two classes: The first one is marked by impaired extralysosomal degradation of proteins, catabolic PAM, encompassing desmin-related myopathies. Mutant proteins, that is, desmin, myotilin, or α-B crystallin, defy protein degradation, aggregate and associate with other proteins within muscle fibers, hence marking desminopathies, myotilinopathies, and α-B crystallinopathies. A second class of PAM encompasses those apparently associated with developmental errors though, again, based on mutations in genes for myofibrillar proteins, foremost sarcomeric actin and myosin. Here, actinopathies and myosinopathies often occur early in childhood while catabolic PAMs are largely of adult or even late onset. The common principle of these PAMs is that immunohistochemical identification of certain proteins resulted in subsequent molecular analysis of respective genes, identification of mutations, and demonstration of mutant proteins as important components of these protein aggregates.