The development of in vivo positron emission tomography (PET) imaging for microglia, using a ligand for translocator protein (TSPO), a protein present on the mitochondrial membrane and upregulated in neuroinflammation [12], has demonstrated microglial activation in Alzheimer’s disease [13]; although how the radioligand relates to the functional state of microglia is still unknown. Here, TSPO is linked to early-onset autosomal dominant Alzheimer disease.