TREM2 and Alzheimer disease: TREM-2 alterations, mainly due to TREM-2 mutations causing a loss-of-function, are also related to a variety of neurodegenerative diseases, including AD, PD, MS, Frontotemporal Dementia (FTD), and Amyotrophic Lateral Sclerosis (ALS) [25,26,27,28,29].