Two enzymes of the GSH cycle were not altered in the AD prefrontal cortex: GSS, the final step in GSH synthesis (Figure 3N), and glutathione reductase (GSR) (Figure 3O), which uses nicotinamide adenine dinucleotide phosphate (NADPH) to reduce glutathione disulfide back to GSH. The gene discussed is GSR; the disease is Alzheimer disease.