Mutations in triggering receptor expressed in myeloid cells 2 (TREM2), expressed by microglia and other macrophages, have been linked to an increased risk of AD,12 and several studies on the soluble form of the protein TREM2 (sTREM2) have revealed increased CSF concentrations in patients with AD compared to controls.13, 14, 15, 16. The gene discussed is TREM2; the disease is Alzheimer disease.