An increase in the role of glycolysis in ATP production was shown by calculating of the bioenergetic health index ratio of fibroblasts with the mutations m.8993T > G (MT-ATP6) m.9185T > C (MT-ATP6), m.10158T > C (MT-ND3) and m.12706T > C (MT-ND5), which are associated with Leigh syndrome, developmental delay, abnormal gait, myopathy, epilepsy, dystonic tetraparesis and severe neonatal lactic acidosis [83]. The gene discussed is MT-ND5; the disease is Leigh syndrome.