Caspase-3 activation leads to DNA fragmentation so we performed the TUNEL assay in muscle biopsies from patients with TK2 mutations (P3, P4), a patient with SUCLA2 mutations (P10, Table 1) and patients with confirmed mitochondrial encephalomyopathy (P6, P7 and P12). This evidence concerns the gene TK2 and mitochondrial encephalomyopathy.