The most significant pathologic finding in muscular dystrophy(MD) is muscle fiber necrosis followed by regeneration. A membrane hypothesis to explain fiber necrosis seems to be confirmed by the discovery of dystrophin and dystrophin-associated glycoprotein (DAG); both are located along the muscle surface membrane. However the mechanism of muscle fiber degeneration cannot be fully explained by the membrane theory itself, because the gene product of Emery-Dreifuss MD is present in the nuclear membrane. Heterogeneous clinical expressions of mitochondrial diseases are also puzzling and have been explained by "tissue specificity" due to different population of wild and mutant mitochondrial DNA from tissue to tissue. The tissue with higher percentage of mutant mitochondrial DNA may not function in an "all-or-none" manner.