CD200 and MELAS: Moreover, numerous mitochondrial DNA (mtDNA) encoded genes have other rare variants that can cause MELAS; these include mtDNA encoded tRNAs (MT-TS1, MT-TS2, MT-TW, MT-TC, MT-TL2, MT-TK, MT-TH, MT-TQ, MT-TF, and MT-TV) and mitochondrial respiratory chain (MRC) complex I (MT-ND1, MT-ND5, and MT-ND6), complex III (MT-CYB), and complex IV (CIV) subunits (MT-CO2 and MT-CO3).