Diagnosis of Parkinson disease (PD) currently relies on clinical symptoms, and is often made late into the disease. Immunostaining for α-synuclein in gastric mucosa samples might aid earlier diagnosis of PD, a new study shows. Mucosa biopsies were positive for α-synuclein in 17 of 28 patients with PD, one of six individuals with mild presymptomatic parkinsonism, and only one of 23 healthy controls.