The present study aims to evaluate the benefit and the cost of a diagnosis strategy based on the combined use of 2 techniques named "Surveyor Nuclease" and "Mitochip". Surveyor nuclease is a mismatch-specific DNA endonuclease that will be used for screening the entire mtDNA in order to identify heteroplasmic mutations. In absence of any identified mutation, another technique based on the use an oligonucleotide sequencing microarray (MitoChip) will be performed for the identification of homoplasmic mutations. Mitochip is an array-based sequencing platform for rapid and high-throughput analysis of mitochondrial DNA.