TREM2 and early-onset autosomal dominant Alzheimer disease: Triggering receptor expressed on myeloid cells 2 (TREM2), a member of the immunoglobulin superfamily, binds lipids, transmits intracellular signals via the adaptor DNAX-activating protein of 12 kDa (DAP12) and plays a critical role in the pathogenesis of Alzheimer’s disease (AD) [15].