TK2 and lactic acidosis: The highest levels were detected in two patients with POLG mutations (85252 pg/mL and 13215 pg/mL) followed by P4 of this study carrying TK2 mutations (8000 pg/mL) and a patient with lactic acidosis and epilepsy bearing the mtDNA A3243G mutation (P12), (6999 pg/mL).