The human mitochondrial DNA (mtDNA)is a 16569 bP closed circular double helix molecule.It codes for 13 subunits of oxidative phosphorylation (OXPHOS ) enzyme plus the structural rRNAs and tRNAs. Over the past years,a number of mtDNA mutations that cause human diseases have been identified,such as blindness,deafness,cardiac failure,and human degenerative diseases. Mitochondrial DNA diseases may be much more common than previously thought.