Parkinson's Disease is the second most common neurodegenerative disorder. The focus of the disease is the progressive degeneration of dopamine-producing nerve cells in a certain region of the midbrain, the substantia nigra. Misfolded proteins are the cause. Until recently, it was unclear why damage is confined to specific nerve cells. A team of researchers has now defined how this selective disease process begins using a genetic mouse model of Parkinson's disease.