Genetic diseases of muscle.

In the last twenty years, the genetic basis for most of the inherited myopathies and muscular dystrophies has been unveiled. Diseases have been found to result from loss of function of structural components of the muscle basal lamina (e.g., MCD1A), sarcolemma (e.g., the sarcoglycanopathies), nucleus (e.g., EDMD) and sarcomere (e.g., the nemaline myopathies). A few have been associated with abnormalities in the genes for muscle enzymes (e.g., calpain and fukutin). Alternate mechanisms of pathogenesis have also recently been suggested by mutations lying outside of coding regions, such as the "field effect" of chromosomal mutations in DM2. In the future, we will likely identify the genes responsible for the remaining disorders, including many of the distal myopathies. In addition, we may also find skeletal muscle diseases associated with some of the presently non-implicated muscle proteins: syntropin, dystrobrevin, epsilon-sarcoglycan and sarcospan. The next steps may be to identify and understand the relationship of modifier genes producing the phenotypic heterogeneity of many of these diseases and to characterize those and other targets for therapeutic intervention, whether by gene therapy or by pharmacological treatment.