The activity of certain enzymes, such as aconitase 2 (an enzyme of the Krebs cycle), was found to be reduced in the lymphocytic mitochondria of aged persons, patients with mild cognitive impairment (MCI) and AD, being negatively correlated with the levels of plasmatic antioxidant vitamins and directly proportional to the mini mental state examination score, suggesting a significant contribution of the oxidative damage of aconitase 2 to the energetic imbalance and cognitive dysfunction with increasing age [80]. The gene discussed is ACO2; the disease is Alzheimer disease.