In a study involving 17 PD with history of falls, 27 PD non-fallers and 15 healthy controls, 1-[11C]methylpiperidin-4-yl propionate ([11C]PMP) position emission tomography (PET) imaging was used to evaluate cholinergic terminal integrity by measuring the presence of the enzyme acetylcholinesterase (AChE).55 Cortical activity represented NBM integrity and thalamic uptake reflected PPN integrity. The gene discussed is ACHE; the disease is Parkinson disease.