Microgliosis is observed in numerous neurological disorders, and only recently evidence has been presented that TREM2‐dependent microglial functions appear to be protective in AD models (Ulland et al, 2017; Focke et al, 2019; Parhizkar et al, 2019), AD patients (Ewers et al, 2019), and models of retinal degeneration (O'Koren et al, 2019). The gene discussed is TREM2; the disease is Alzheimer disease.