Mitochondrial diseases are the most frequent metabolic diseases (2.5 persons among 10 000) and are clinically heterogeneous making diagnosis particularly challenging for clinicians. Molecular analysis of mitochondrial DNA (mtDNA) is a critical step in diagnosis and genetic counselling of respiratory chain defects. DNA sequencing remains the gold standard but it is time-consuming and fails to detect mutations that may be present at a low heteroplasmic level (20% or below); therefore the diagnosis is yet based on the detection of a few number of pathogenic mutations. 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. The economical study will compare the cost of these techniques to the standard diagnosis method in term of direct and indirect costs