MAPT and tauopathy: Pathologically, PSP is classified as a primary four-repeat (4R) tauopathy, distinguished by the accumulation of hyperphosphorylated tau proteins, forming cellular inclusions in neurons, oligodendrocytes, and astrocytes, located predominantly in subcortical structures—basal ganglia, subthalamic nucleus, substantia nigra—and brainstem, with cortical involvement in some variants [5, 6].