MAPT and Alzheimer disease: Furthermore, Shimada et al. (2022) generated forebrain organoids from patients with familial AD and observed Aβ pathology and an increased presence of phosphorylated tau protein in the organoids, which is a hallmark of the pathology of AD; tau fibrils were also observed in cell bodies and the neurites of organoids that were injected with adeno-associated virus-expressing mutant tau (P301L).