Mihondrial cytopathies are mutations in the inherited maternal mihondrial genome, or the nuclear DNA-mutation. Mihondrial respiratory chain disorders (RCD) are a group of genetically and clinically heterogeneous diseases, due to the fact that protein components of the respiratory chain are encoded by both mihondrial and nuclear genomes and are essential in all cells. In addition, the biogenesis, structure and function of mihondria, including DNA replication, transcription, and translation, all require nuclear encoded genes. Since mihondria are present in every cell, every tissue, mihondrial disorder usually affects multiple organs.