Previous studies have demonstrated the utility of labelled L-deprenyl with PET for mapping of MAO-B in the human brain,7, –9 and clinical PET studies have shown its application in Alzheimer’s disease,10, , , –14 epilepsy,15, –17 Creutzfeld–Jakob disease,18 amyotrophic lateral sclerosis,1 traumatic brain injury19 and evaluation of MAO-B inhibitors.20, , –23 This technique also holds relevance for studying multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system characterised by demyelination of neuronal axons. The gene discussed is MAOB; the disease is amyotrophic lateral sclerosis.