Mitochondrial aconitase, succinyl-CoA synthetase β, fumarase and malate dehydrogenase showed decreased gene expression in hippocampal samples from autopsy AD brains in two independent studies (40, 41) Mitochondrial oxoglutarate dehydrogenase, showed increased and decreased gene expression in moderate and severe AD patients (40). Here, PHGDH is linked to Alzheimer disease.