ATM and early-onset autosomal dominant Alzheimer disease: Though microglia were traditionally assumed to be a homogenous cell population, next generation sequencing analyses have demonstrated a spectrum of transcriptional states with distinct subclusters emerging under different conditions, such as early brain development (termed “axon tract-associated microglia”, ATM) [20], Alzheimer’s disease pathogenesis (termed “disease-associated microglia, DAM) [17], and other neurodegenerative diseases or aging (termed “microglial neurodegenerative phenotype”, MGnD) [18].