A subset of heterozygous TREM2 variants such as R47H, R62H and H157Y are associated with increased risk of Alzheimer's disease (AD) (Guerreiro et al, 2013; Jonsson & Stefansson, 2013; Jonsson et al, 2013; Slattery et al, 2014; Finelli et al, 2015; Ghani et al, 2016; Jiang et al, 2016). This evidence concerns the gene TREM2 and early-onset autosomal dominant Alzheimer disease.