Parkinson's disease is a neurodegenerative disease. The nerve cells in the brain that are responsible for the production of the important messenger substance dopamine progressively deteriorate. The reasons for this are yet to be fully understood.
These nerve cells are located mainly in a specific region of the brain called the substantia nigra. The substantia nigra is mainly responsible for the coordination and fine-tuning of the body’s movements. The decrease in dopamine-containing nerve cells leads to an imbalance of the messenger substances in the brain, which is considered to be the cause of the typical movement-related (motor) symptoms of Parkinson's disease, such as tremor, muscle stiffness, and slowing of movement. While dopamine is the main neurotransmitter involved, other neurotransmitters are also affected. This may explain why simply replacing dopamine does not necessarily improve symptoms. It may also help to explain why so many people with Parkinson’s also experience non-motor symptoms.
Rare genetic forms of Parkinson's disease are common in some families, (i.e. the disease is inherited). In most cases, Parkinson's disease is not inherited, and the causes of the disease are unknown.