In a recent study, Holmqvist et al. (2014) isolated three different types of alpha-synuclein (aggregated, monomeric and oligomeric) from the brain lysate of a patient with PD and directly injected them into the submucosa of the ENS in mice to test the hypothesis that alpha-synuclein could propagate from the ENS to the CNS by way of the vagus nerve. Here, SNCA is linked to Parkinson disease.