GRN and Alzheimer disease: Progress in single-cell transcriptomic techniques has facilitated the understanding of microglia heterogeneity and revealed multiple disease-specific microglia subclusters [8, 9], including disease-associated microglia (DAM) in Alzheimer’s disease (AD) [10], lipid-droplet-accumulating microglia (LDAM) in aging [11], oxidized phosphatidylcholines (OxPC) clearing associated microglia in MS [12, 13], Fn1+ microglia in spinal cord injury [14], and Grn+ microglia in TDP-43 proteinopathy [15].