Mitochondrial DNA Mutations, Pathogenicity and Inheritance

Mitochondria contain their own DNA (mtDNA), which codes for 13 proteins (all subunits of the respiratory chain complexes), 22 tRNAs and 2 rRNAs. Several mtDNA point mutations as well as deletions have been shown to be causative in well-defined mitochondrial disorders. A mixture of mutated and wild type mtDNA (heteroplasmy) is found in most of these disorders. Inheritance of mtDNA is maternal, and mothers with heteroplasmic mtDNA transmit different proportions of normal and mutated mtDNA to the children. Mitochondrial tRNA genes have a central role in mitochondrial gene expression at the level of transcription, RNA processing and protein synthesis and they appear to be the mitochondrial genes most frequently affected by mutations causing diseases in man.