Amongst the affected enzymes of TCA cycle, activity of α-ketoglutarate dehydrogenase, pyruvate dehydrogenase and isocitrate dehydrogenase have been reported to be markedly decreased in autopsied brains of AD patients while the activity of succinate dehydrogenase and malate dehydrogenase have been shown to be markedly increased [35]. Here, PHGDH is linked to Alzheimer disease.