With this project, continuation of other precedents, the aim is to identify new mutations in mtDNA genes and to characterise the pathogenic mechanism in models of transmitochochondrial cybrides that contain a nuclear background of neuroblastoma, which can be differentiated in neurons, and with human adult mesenchymal stem cells, which can be differentiated in muscle, since neurons and muscle are the tissues most affected in mitochondrial diseases. Mitochondrial Diseases are a series of disorders, with very diverse clinical manifestations, which have in common that they are produced by defects in the biosynthesis of cellular energy in the form of ATP. The diagnosis of patients with these pathologies is poor and their treatment is very limited or non-existent. Mitochondrial DNA is perfectly characterised and has been associated with a large number of point mutations and deletions that cause these diseases. However, only 16 % of patients have reached the genetic diagnosis, leaving the rest undiagnosed. Objective: Sequence the complete mitochondrial DNA (16,569 bp) of samples from our DNA bank from patients with mitochondrial disease, to find new mutations that cause the pathology. In addition, the pathogenic mechanism of these mutations will be studied through the use of transmitochondrial cybrides of neuron cell lines and myocytes. Methodology: Sequencing of complete mitochondrial genomes. The study mechanism of pathogenicity shall be carried out by the construction of transmitochochondrial cybrides containing mutated mtDNA. They will perform analyses of different parameters related to the mitochondrial function: growth in galactose, respiratory chain activity, ROS production, cell viability, mitochondrial internal membrane potential, calcium levels, ATP levels and synthesis, and analysis of RNA and protein synthesis.