Mitochondrial diseases affecting the OXPHOS are a heterogeneous group of prevalent genetic disorders transmitted either by maternal inheritance due to mutations in mtDNA genes (encoding 13 MRC core subunits, 2 mRNAs, 22 tRNAs) or by Mendelian inheritance due to mutations in nuclear genes encoding the remaining MRC subunits or one of the numerous assembly, transcription, translation and replication factors needed for mtDNA and OXPHOS maintenance. This evidence concerns the gene CD200 and inborn mitochondrial metabolism disorder.