TREM2 and early-onset autosomal dominant Alzheimer disease: TREM2 is pivotal in regulating the survival, proliferation, and phenotypic transition of microglia/macrophages, particularly in the disease-associated microglia (DAM) phenotype, which plays an integral role in the response to the Alzheimer’s disease (AD) pathology, including amyloid-beta plaque clearance and the modulation of neuroinflammation.