We have previously shown CSF levels of soluble TREM2 to be increased in the prodromal at-risk state of Alzheimer’s disease (Suarez-Calvet et al., 2016b), preceding the estimated age of onset of dementia symptoms by ∼5–10 years as estimated in autosomal-dominant Alzheimer’s disease (Suarez-Calvet et al., 2016a). The gene discussed is TREM2; the disease is Alzheimer disease.