One oxidant enzyme is nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) that increases its activity, generating more ROS, together with a decrease in antioxidant enzymes such as superoxide dismutase, catalase, etc. Additionally, alteration in the respiratory chain in the mitochondria is associated with AD due to the increased ROS. This evidence concerns the gene FMO5 and Alzheimer disease.