BioEd Online

An immense database of Parkinson's disease patients is being launched in California. Medical researchers say the database will be essential for tracking down the causes of the disease.

Once established, the state-wide registry will be the biggest for the disease in the world. It gained formal approval in late September when Governor Arnold Schwarzenegger signed a bill requiring doctors to register every new patient diagnosed with the movement disorder in a central database.

Researchers say the new registry will be crucial for pinning down which environmental factors, such as pesticides or diet, are important in triggering the disease. This has become a priority with the growing realisation that genes alone cannot explain people's risk.

Nailing the culprits

Parkinson's is caused when dopamine-producing cells in the brain die or are damaged, causing symptoms such as tremors, stiff or slow movement and problems with balance.

Although the disease is thought to affect as many as 2% of people, researchers have struggled to build up an accurate picture of the types of people it strikes. Unlike cancer, for example, the disease is rarely recorded as a cause of death because patients succumb to other conditions.

Genes alone are thought to explain only a tiny fraction of cases. At the same time, numerous studies have suggested that there may be a wide range of environmental triggers, from polluting metals and solvents to diet and head trauma, but no clear-cut cause has been found. "We have a lot of hints but no smoking gun," says William Langston, director of the Parkinson's Institute in Sunnyvale, California, who joined other neurologists and patient advocacy groups in campaigning for the registry.

Researchers now believe that people with the right combination of genes and environmental triggers develop the disease. For example, pesticides may have a greater impact on the brain cells of people genetically susceptible to their effects. If at-risk groups can be identified, individuals might be able to change their lifestyle to ward off the disease.

Armed with the new database, researchers will be able to identify patients they are keen to study and approach them for further information about their medical history and exposure to environmental triggers. They are particularly keen to test the idea that the disease is brought on by contact with pesticides or other toxic chemicals. California has been logging the use of these chemicals for the past 25 years.

Strength in diversity

At present, scientists tend to collect and study groups of Parkinson's patients within a certain region or clinic. But these groups are often small and do not accurately represent the full range of patients in the wider population.

Some efforts have been made to build up larger studies. Nebraska already runs a registry, for example, and information on Parkinson's patients is also collected nationally in Denmark.

But the 35-million population of California means that the new registry could enrol as many as 5000 patients each year, and the state's diversity means it will span a range of socio-economic groups and ethnicities, as well as rural and urban areas.

"This could be the final step towards finding the environmental triggers for the disease," says Langston.

A two-year pilot project, funded by $0.5 million from the US National Institute of Environmental Health Sciences and the Michael J. Fox Foundation for Parkinson's Research, will determine how best to create and run the registry. After this, it is unclear how the registry will pay its way, although the organisers say they are confident they will secure financing.

"It has the potential to be a powerful tool," says epidemiologist Carl Counsell, who studies Parkinson's disease at the University of Aberdeen, UK. But he warns that the new registry may still miss some patients, because many go undiagnosed.