For both conditions, the majority of variants have been identified in specific mitochondrial encoded genes (MTTL1, MTTQ, MTTH, MTTK, MTTC, MTTS1, MTTND1, MTND5, MDTN6, and MTTS2); however, variants in POLG, which is one of the NEMP genes, have also been identified to cause MELAS [10]. This evidence concerns the gene POLG and MELAS.