Parkinson's disease kills the cells that produce dopamine in the brain, according to National Institute of Neurological Disorders and Stroke. This loss of dopamine damages the motor functions of the brain, which causes the symptoms of Parkinson's disease.
Parkinson's disease slowly breaks down the brain's ability to control movement, causing tremors, stiffness, slowness of movement and instability, National Institute of Neurological Disorders and Stroke says. Tremors tend to be concentrated in the hands, arms, jaw and face. Stiffness tends to affect both the limbs and the trunk. Symptoms are subtle at first and progress only gradually, although the rates of progression vary between sufferers. Later symptoms include emotional changes, difficulty chewing and swallowing, constipation and urinary problems.
As of 2015, Parkinson's disease has no cure, according to National Institute of Neurological Disorders and Stroke. However, there are effective treatments available to mitigate its symptoms. Most patients are given a combination of medications, including a drug that turns into dopamine in the body and a second drug that prevents the conversion until the first reaches the brain. Adequate dopamine allows the motor functions of the brain to proceed more normally. This treatment is more effective for stiffness and slowness of movement than it is for tremors.