When lysosomal function declines, specific proteins, including tau, α-synuclein, and transactive response DNA binding protein of 43 (TDP-43), can accumulate within nerve cells, contributing to the onset of neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). Here, MAPT is linked to Alzheimer disease.