Mutations and polymorphisms of the TREM2 gene are associated with a significant increase in the risk of AD (Jonsson et al., 2013; Cuyvers and Sleegers, 2016), but it will not increase the risk of Amyotrophic Lateral Sclerosis (ALS) and PD (Zhang et al., 2020). Here, TREM2 is linked to Alzheimer disease.