Elevated levels of an enzyme called PHGDH in the blood of older adults could be an early warning sign of Alzheimer’s disease, and a study led by the University of California San Diego provides new evidence to support this claim. In analyzing brain tissue, researchers observed a trend consistent with their previous findings in blood samples: expression levels of the gene coding for PHGDH were consistently higher in adults with different stages of Alzheimer’s disease, even the early stages before cognitive symptoms manifested.