TREM2 and Alzheimer disease: The rare protein coding variants in TREM2, R47H, and R62H, which are reproducibly associated with increased risk for developing AD, are being intensively studied as these variants were the first coding variants in an innate immune gene that have been reproducibly shown to alter risk for AD (Cruchaga et al, 2013; Jin et al, 2015; Lill et al, 2015).