To date, these genes are screened by sequencing methods that are not able to detect large-scale rearrangements. In order to detect possible large-scale rearrangements, the investigators propose to develop a new assay based on QMPSF (Quantitative Multiplex PCR of Short fluorescent Fragments) able to detect exon deletions and duplications. the investigators propose to screen the POLG gene by QMPSF in at least twenty patients with either no mutation or only one mutation detected in POLG and no mutation in other genes such as TWINKLE and ANT1.