Progranulin is critical for maintaining lysosomal function (5, 6, 7), and FTD-GRN patients show signs of lysosomal dysfunction, including accumulation of lysosomal proteins (64) and lysosomal storage material (79), abnormal lysosomal enzyme activity (48), and elevated levels of extracellular vesicles in plasma and brain tissue (80). Here, GRN is linked to frontotemporal dementia.