In longitudinal cohorts comprising healthy adults or those with MCI, the gradient of blood GFAP elevation is greater in those who evolve to dementia.35,36 Among CU adults, a higher baseline blood GFAP is associated with the development of clinical AD and more rapid decline in hippocampal volume.37 Taken together, our findings support the notion that GFAP elevation is an early and inexorably progressive event in AD pathology, with the gradient and tempo of escalation providing useful clinical information. Here, GFAP is linked to Alzheimer disease.