For example, single-nucleotide polymorphisms in TREM2 confer increased risk for AD (14), and human neuropathology studies have shown that these TREM2 risk variants are associated with several changes in the brain including reduced numbers of microglia per amyloid plaque (15, 16) and a change in the distributional pattern of disease (17). This evidence concerns the gene TREM2 and Alzheimer disease.