Cognitive decline in Alzheimer’s disease differs substantially from one person to the next and is not well predicted by existing medical tests. Among people with preclinical Alzheimer’s disease who began one of two related studies with no symptoms, researchers from the Keck School of Medicine of USC found three distinct patterns: stable, slow cognitive decline and fast cognitive decline. About 70% of participants remained stable over the study period of approximately six years. For the study, researchers analyzed data from the Anti-Amyloid Treatment in Asymptomatic Alzheimer’s Disease (A4) study, a clinical trial of the monoclonal antibody solanezumab. They also included data from the Longitudinal Evaluation of Amyloid Risk and Neurodegeneration Extension (LEARN), a companion study of people without the elevated levels of amyloid-beta in the brain which are an early sign of Alzheimer’s disease. Before and during the trial, participants completed a series of cognitive tests that measured their memory, attention and thinking. Scores on these tests were used to track their rate of cognitive decline. The researchers also collected brain scans and blood tests, including phosphorylated tau (P-tau217), a marker of the protein tau, one of the hallmarks of Alzheimer’s disease. Participants who showed a gradual or a fast decline had higher P-tau217 levels when the study began, as well as higher levels of tau on brain scans than those who remained stable. They also had a smaller hippocampus, an area of the brain linked to memory and one of the first affected by Alzheimer’s disease. Using biomarker data, the researchers could correctly predict whether participants were likely to stay stable or worsen about 70% of the time.