TREM2 and early-onset autosomal dominant Alzheimer disease: A functional TREM2 single nucleotide polymorphism is important in the etiology of Alzheimer's disease (AD) (Guerreiro et al., 2013) and frontotemporal dementia (Giraldo et al., 2013), and TREM2 mRNA is increased in monocytes in AD (Hu et al., 2014).