Although the causes of certain types of parkinsonism have been identified, the cause of Parkinson's itself remains unknown.
We don’t yet know exactly why people get Parkinson's, but researchers think that a combination of genetic and environmental factors cause dopamine-producing nerve cells to die.
Parkinson's occurs due to a loss of nerve cells in the brain. The symptoms of Parkinson's emerge when around 70% of cells have been lost.
It is not known why these nerve cells die.
We fund research exploring the causes of Parkinson's. We need to know how and why certain nerve cells in the brain die in Parkinson's in order to find a cure.
The nerve cells that die and lead to the development of Parkinson's are responsible for producing a chemical known as dopamine.
Dopamine allows messages to be sent to the parts of the brain that co-ordinate movement.
With the loss of dopamine-producing nerve cells, these parts of the brain are unable to work normally, causing the symptoms of Parkinson's to appear.
The level of dopamine then continues to fall slowly over many years, causing symptoms to further develop and new symptoms to appear.
It is generally thought that people develop Parkinson's due to a combination of environmental factors and genes that increase its possibility.
It is extremely rare for people to pass on Parkinson's to their children.
It is estimated that Parkinson's may have a genetic cause for 5 in every 100 people with the condition.
In the rare examples where Parkinson's does seem to be passed on from one generation to the next, genetic abnormalities appear to be involved.
Even when an abnormal gene is present the chances of going on to develop Parkinson's are very low.
Researchers are interested in the role of genes which cause inherited Parkinson's as it may help them understand the process of nerve cell death.
DJ-1 is one of several genes known to be linked to some inherited forms of Parkinson's. Research into how mutations in this gene affect the nerve cells in Parkinson's is ongoing.
Changes or mutations in the parkin gene are also linked to some forms of early onset Parkinson's (when people are diagnosed under the age of 40).
But it is not known how these changes in parkin lead to the death of nerve cells in Parkinson's.
You can read more on genetic research in our Inherited Parkinson's and genetic testing information sheet.
There is some evidence that environmental factors (toxins) may cause dopamine-producing neurons to die, leading to the development of Parkinson's.
The term 'environment' refers to the world around you and the pathogens (viruses and bacteria), toxic chemicals and heavy metals that occupy it.
In particular, there has been a great deal of speculation about the link between the use of herbicides and pesticides and the development of Parkinson's.
There was a case in 1982 where a small number of drug users in California mistakenly took heroin contaminated with a dangerous synthetic drug called MPTP.
Anyone who took the MPTP-contaminated heroin developed very severe and irreversible Parkinson's-like symptoms almost immediately. These unlucky people became known as the 'frozen addicts'.
However, this incident has led to significant scientific advances. MPTP has since been used widely in research and helped scientists learn much more about Parkinson's.
There are many other examples of different environmental factors leading to the development of Parkinson's, but as yet the evidence is inconclusive.
Take a look at our research news for more on the latest developments.