Parkinson’s disease (PD) occurs when brain cells that make dopamine, a chemical that coordinates movement, stop working or die. Because PD can cause tremor, slowness, stiffness, and walking and balance problems, it is called a “movement disorder.” But constipation, depression, memory problems and other non-movement symptoms also can be part of Parkinson’s. PD is a lifelong and progressive disease, which means that symptoms slowly worsen over time.