Alternative biomarkers beyond TSPO are avidly sought to develop PET tracers targeting markers of specific cell types involved in neuroinflammation.29,31,32 Monoamine oxidase-B (MAO-B) has been explored as a PET neuroinflammatory biomarker using [11C]L-deprenyl-D2,33 as this target is primarily expressed on astrocytes as revealed by microautoradiography with [3H]L-deprenyl.34 Furthermore, in the spinal cord from patients diagnosed with motor neuron disease, MAO-B expression co-localized to reactive astrocytes labelled for glial fibrillary acidic protein (GFAP), a selective astrocyte marker. This evidence concerns the gene GFAP and motor neuron disorder.