In Parkinson's disease, certain nerve cells (neurons) in the brain gradually break down or die. Many of the symptoms are due to a loss of neurons that produce a chemical messenger in your brain called dopamine. When dopamine levels decrease, it causes abnormal brain activity, leading to impaired movement and other symptoms of Parkinson's disease.

The cause of PD is unknown, with both inherited and environmental factors believed to play a role, including:

• Genes; researchers have identified specific genetic mutations that can cause Parkinson's disease. But these are uncommon except in rare cases with many family members affected by Parkinson's disease;

• Environmental triggers; exposure to certain toxins or environmental factors may increase the risk of later Parkinson's disease, but the risk is relatively small.

Researchers have also noted that many changes occur in the brains of people with Parkinson's disease which include:

• The presence of Lewy bodies; the inclusion bodies – abnormal aggregations of protein – that develop inside nerve cells;

• Alpha-synuclein found within Lewy bodies; the aggregation of alpha-synuclein in Lewy bodies appears to be a link between reduced DNA repair and brain-cell death in PD.

Parkinson's disease can't be cured, although surgery to place microelectrodes for deep brain stimulation has been used to reduce motor symptoms in severe cases where drugs are ineffective.

More Info: en.m.wikipedia.org