Triggering receptor expressed on myeloid cells 2 (TREM2), a type I transmembrane glycoprotein expressed on microglia, dendritic cells, osteoclasts and other tissue-resident macrophages, can be shed from the cell surface and is a potential biomarker for Alzheimer`s disease (AD) in CSF [1–4]. The gene discussed is TREM2; the disease is Alzheimer disease.