CD200 and mitochondrial disease: 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.