In this study, we used cultured BV‐2, CHME‐3 and iPSC‐derived microglia to show that expression of R47H TREM2 in microglia increases phagocytosis of synapses and increases neuronal loss, indicating a gain‐of‐function relative to wild‐type TREM2, which might contribute to the increased AD risk conferred by R47H TREM2. This evidence concerns the gene TREM2 and Alzheimer disease.