SOD3 is an extracellular enzyme, and SOD2 is active in mitochondria, with several structural differences (Fig. 3).26 The gene for SOD2 enzyme is found on Chromosome 6, and abnormalities of Chromosome 6 have been associated with Alzheimer’s disease, indeed with 120 additional disorders.27 SOD2 has a metalloenzyme antioxidant activity and is dependent on the transition metal Mn, which is inserted into the complex when SOD2 is newly synthesized. Here, SOD2 is linked to early-onset autosomal dominant Alzheimer disease.