The study of dGAE Tau (297–391) aggregation by time-resolved cryo-EM showed that disease-specific tau (chronic traumatic encephalopathy—CTE and Alzheimer’s disease—AD) filaments arise from the same filament intermediate (FIA—first intermediate amyloid) during the initial phase of aggregation. This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.