Apart from the nucleus, the mitochondrion is the only organelle of an animal cell that contains its own genome. Mitochondrial DNA is much less in size than the nuclear one and codes for only several dozens of biological macromolecules. Nevertheless, mutations in mitochondrial genes often result in the occurrence of serious hereditary neuromuscular diseases. New mitochondrial DNA mutations and their relations to clinical symptoms are continuously reported in the scientific literature. In this review, we summarize existing data about such mutations, and also about contemporary gene therapy approaches that have been developed for their suppression.