Parkinson’s does not occur more often in identical twins
During the same period, and at the same Parkinson Institute in Sunnyvale, California, researcher Carlie Tanner also carried out important work. Bloem explains: “Her hypothesis was simple: if Parkinson’s were a hereditary disease, then identical twins who share identical DNA should both develop the disease much more often than fraternal twins, as we see, for example, with diabetes.” But that turned out not to be the case.
“As a result, two enormous breakthroughs emerged from the same lab almost simultaneously,” Bloem says. “Langston’s research showed that an external substance can cause Parkinson’s, and Tanner’s work showed that heredity plays only a limited role. Together, those discoveries unmistakably pointed to the environment as the primary cause.”
These insights formed the starting point for new research into pesticides. “When researchers exposed laboratory animals to these substances, they developed Parkinson-like symptoms, and damage occurred specifically in the substantia nigra of the brain, the area involved in Parkinson’s disease.” According to Bloem, this is convincing evidence of a causal relationship.
Parkinson’s occurs in clusters
A third important study comes from Canadian neurologist André Barbeau, who in 1987 investigated in the province of Quebec the extent to which the environment plays a role in the development of Parkinson’s. If the disease had been evenly distributed throughout the region, that would have pointed to a hereditary or random cause. But that was not the case: Parkinson’s occurred in clear clusters.
Moreover, those clusters were located precisely in areas where high concentrations of pesticides were found in the groundwater — a third strong indication that environmental factors play a causal role.
A call to politicians
“The most hopeful thing,” says Bloem, “is that Parkinson’s appears to be at least partly and I believe largely preventable. That is revolutionary: a brain disease we can prevent through better environmental policy.” Yet hardly any investment is made in this. “In the United States, only 2 percent of Parkinson’s research funding goes toward prevention. In contrast, billions are spent on treatments instead of turning off the tap.”
According to him, it is therefore time for a shift: “In healthcare, we wait until things go wrong and then intervene with expensive solutions. Yet prevention can save enormous suffering as well as costs.” The Netherlands is doing slightly better than many other countries. “Some toxic substances, such as Paraquat, are banned here, and as a result the growth seems to be leveling off somewhat, especially compared to countries such as the United States or China where environmental pollution is far more severe,” says Bloem. “But even in the Netherlands, thousands of new patients are still diagnosed every year. So that is absolutely no reason to sit back and relax."
