From the PDS website

Parkinson's is a progressive neurological condition affecting movements such as walking, talking, and writing. It is named after Dr. James Parkinson (1755-1824), the London doctor who first identified Parkinson's as a specific condition.

Parkinson's occurs as result of a loss of nerve cells in the part of the brain known as the substantia nigra. These cells are responsible for producing a chemical known as dopamine, which allows messages to be sent to the parts of the brain that co-ordinate movement. With the depletion of dopamine-producing cells, these parts of the brain are unable to function normally.

SIGNS AND SYMPTONS

The symptoms of Parkinson's can be classified as motor and non-motor. Motor symptoms define Parkinson's, with three primary features:

1. Tremor - which usually begins in one hand. This is the first symptom for 70% of people with Parkinson's.

2. Slowness of movement (bradykinesia) - people with Parkinson's may find that they have difficulty initiating movements or that performing movements takes longer.

3. Stiffness or rigidity of muscles - problems with activities such as standing up from a chair or rolling over in bed may be experienced.

Various non-motor symptoms may also be experienced, for example:
sleep disturbances
constipation
urinary urgency
depression
Parkinson's is a very individual condition, with each person experiencing different symptoms.

CAUSES

In Parkinson's there is a loss of nerve cells in the part of the brain known as the substantia nigra.

These cells are responsible for producing a chemical known as dopamine, which allows messages to be sent to the parts of the brain that co-ordinate movement.

With the depletion of dopamine-producing cells, these parts of the brain are unable to function normally.

When about 80%of the dopamine has been lost, the symptoms of Parkinson's appear and the level of dopamine will continue to fall slowly over many years.

The reason why the loss of dopamine occurs in the brains of people with Parkinson's is currently unknown. Most researchers believe it is likely that many factors play a role in causing Parkinson's. Areas of research into the cause include genetics and environmental factors.

Genetic research
Scientists have, to date, identified nine genes linked to Parkinson's, of which the parkin gene is most commonly associated with the familial form of Parkinson's. Abnormalities in this gene are particularly prevalent with young-onset Parkinson's disease.
Research will also help to understand which factors are involved in the formation, survival and death of dopamine-producing neurons.

Environment research
There is some evidence that environmental factors (toxins) may cause dopamine-producing neurons to die, leading to the development of Parkinson's. Several toxins have been shown to cause Parkinson's-like symptoms.

There may also be a link between use of herbicides and pesticides and the development of Parkinson's.

To find out more about current research and more please visit the Parkinson's Disease Society website.