While microglia surround Aβ deposits in AD brains, reflecting the phagocytosis of Aβ and/or the formation of barriers against Aβ, TREM2-deficient microglia do not cluster around Aβ deposits, leading to an increased burden of Aβ and worsened axonal dystrophy16,20. The gene discussed is TREM2; the disease is Alzheimer disease.