Howard Hughes Medical Institute (HHMI) researchers have introduced a genetic mutation found in some patients with early onset Parkinson’s disease into mice, creating a new animal model of the disease. Their study adds to growing evidence that Parkinson’s may arise in part from neurons’ failure to recycle the materials used to package and transport neurotransmitters. Inside a neuron, these neurotransmitters are enclosed inside small membrane-bound sacs called vesicles. The vesicles release their contents outside the cell into the synapse—the junction between neurons—by fusing with the outer membrane of the cell. The packaging materials are then quickly recovered by the original cell through a process called endocytosis, which forms new vesicles and ensures that the neuron is prepared to deliver its chemical signals to the synapse again. Several genes involved in this vesicle recycling process have been implicated in Parkinson’s disease. Overall, eight genes that have been linked to Parkinson’s disease encode proteins directly or indirectly involved in endocytosis.