In addition to classical M1- and M2-like phenotypes, a specific subgroup of microglia, which is referred to as disease-associated microglia (DAM), the transition of which is regulated by triggering receptor expressed on myeloid cells 2 (Trem2), is also demonstrated to play a critical role in neurodegenerative diseases sharing similar pathological procedures to mTBI. This evidence concerns the gene TREM2 and neurodegenerative disease.