Parkinson’s disease is a progressive disorder that is caused by degeneration of nerve cells in the part of the brain called the substantia nigra, which controls movement. These nerve cells die or become impaired, losing the ability to produce an important chemical called dopamine. Studies have shown that symptoms of Parkinson's develop in patients with an 80 percent or greater loss of dopamine-producing cells in the substantia nigra.

Normally, dopamine operates in a delicate balance with other neurotransmitters to help coordinate the millions of nerve and muscle cells involved in movement. Without enough dopamine, this balance is disrupted, resulting in tremor (trembling in the hands, arms, legs and jaw); rigidity (stiffness of the limbs); slowness of movement; and impaired balance and coordination – the hallmark symptoms of Parkinson's.

The cause of Parkinson's essentially remains unknown. However, theories involving oxidative damage, environmental toxins, genetic factors and accelerated aging have been discussed as potential causes for the disease. In 2005, researchers discovered a single mutation in a Parkinson’s disease gene (first identified in 1997), which is believed responsible for five percent of inherited cases.

The Parkinson´s prevalence is 60,000 diagnosed cases per year, with an estimate of 1-1.5 million Americans ill,  and the incidence is 18,000 deaths (2003), affecting mostly after the age of 55, but sometimes 30 and 40.

Explanation:

The common symptoms include  involuntary tremor in hands, arms, legs and jaw , muscle stiffness arms, shoulders or neck , gradual loss of movement which often leads to decreased mental skills, changes in voice and facial expression as blinking, swallowing and drooling , stooped posture, unsteady balance  and dementia.

Unfortunately the regular diagnosis methods such as  X-ray or blood test, are not suitable to confirm this disease, only conventional methods such as  two of the three symptoms found in the patient, no more neurological signs found, exclude the tranquilizer medications, head trauma or stroke  patients´usage and try levodopa, dopamine agonists, COMT inhibitors, selegiline, anticholinergic medications or amantadine, which are Parkinson's medication, only to relieve the symptoms, by stimulating the remaining cells in the substantia nigra to increase the levels of dopamine or by decreasing the acetylcholine produced.

Procedures such as surgery, pallidotomy, thalamotomy, and deep brain stimulation are also available procedures to help Parkinson´s extreme symptoms.

On going experimental research  on embryonic stem cells, although political and ethical controversial, might enable scientists to produce dopamine neurons in the laboratory for transplantation into humans offering hope for Parkinson's cure in the future.