TREM2 and Alzheimer disease: In clinical studies, single nucleotide polymorphisms (SNPs) of exon 2 of the TREM2 gene, including rs75932628, rs143332484 and rs2234253, which are closely related to the genetic susceptibility to Alzheimer’s disease (AD) (Sims et al., 2017; Zhou et al., 2019), have not been demonstrated to show a relationship with PD (Li et al., 2016; Mengel et al., 2016).