A number of cybrid cell lines have been created that contain m.3243A > G and m.3271T > C (MT-TL1) mutations associated with MELAS, m.14484T > C (MT-ND6), m.3460G >A (MT-ND1) and m.11778G > A (MT-ND4) mutations associated with LHON, the m.8993T > G (MT-ATP6) mutation associated with Leigh syndrome and NARP, and m.8344A > G and m.8356T > C (MT-TK) mutations associated with MERRF [101,102,103,104,105,106,107]. The gene discussed is TKT; the disease is Leigh syndrome.