A new television documentary re-ignites questions about the existence and potential scientific significance of so-called "clusters" of Parkinson's disease patients. When a larger than expected number of persons develop a disease within a specific time period and within a proscribed location, the group is described as a disease cluster. Clusters can be due to shared exposure to the factors causing the disease, or simply chance occurrences. In the case of a disease like PD, for which the cause is not known, investigating disease clusters may help to identify the cause.

The Canadian TV documentary, entitled "The Parkinson's Enigma," tells of four individuals diagnosed with young onset Parkinson's that decades earlier had all worked together in the same building in Vancouver. The building housed a Canadian Broadcasting Company (CBC) television production crew of roughly 125 people - including actors, writers, production people and technicians - who produced a number of television shows in the 1970s and '80s. The incidence of PD in the general population is estimated at one person in 300, so four cases in a group of 125 would be significant. Michael J. Fox was among the actors who worked in the CBC building and is one of the four people diagnosed with PD.

A growing body of evidence suggests that some PD cases may be caused by exposure to agents in the environment, such as toxins or metals. If there are PD clusters, these will provide enticing research opportunities to determine if patients experienced common exposures or events that may have contributed to their condition. To date, however, limited investigation of the few reported clusters has yielded little significant data on possible links to PD.

Like other areas of PD research, the study of clusters has been held back by a chronic shortage of available funding. Once a true disease cluster has been identified it requires a great deal of scientific "detective work" to even have a chance of finding the potentially offending agent or agents. Recent increases in government and private support for PD research, however, have expanded the search for insight into how toxic exposures may cause PD. Renewed attention in the Vancouver cluster may lead to further investigation, and, ideally, deepened understanding of the cause of PD.

"The Parkinson's Enigma" includes a theory offered by PD researcher Dr. Donald Calne, director of the Neurodegenerative Disorders Centre at the University of British Columbia Hospital. Dr. Calne speculates that PD clusters may provide evidence that the neurological disorder is caused by exposure to a virus. Lacking strong scientific evidence, however, the viral theory is not widely held by PD researchers and clinicians. A number of other possible causes - including exposure to certain bacteria or fungus - are also plausible. Until research identifies the cause or causes of PD all biologically plausible theories should be vigorously pursued.