The largest-ever environmental and occupational risk factor survey in PSP was just published. Irene Litvan of UCSD led a group of sites throughout North America with 284 patients and 284 controls who were friends or non-blood relatives of the patients.
The results corroborate the finding of all three previous such studies that lesser educational attainment is more common in people with PSP. Two of those studies were done by me and my colleagues in New Jersey (1988 and 1996) and the other was in France by Vidal et al (2009).
In this new study, the odds ratio for having earned a college degree was 0.585 (95% confidence interval 0.345 to 0.993, p = 0.047). The only other statistically significant result was that people with PSP reported having drunk well water for an average of 11.7 years, while for the controls, the figure was 7.4 years. That p-value after multivariate correction, was 0.032. They showed that these two findings were not correlated to each other in this subject group.
Interestingly, the well-documented tendency in Parkinson’s disease for non-smoking was not observed. In fact, there was a non-significant trend in the opposite direction, with the odds ratio of 1.096 (multivariate corrected p = 0.082) for smoking among the PSP group relative to controls.
So what’s the take-home? We’ve been saying for years that most of the diseases for which we have no clear cause (most cases of cancer, Alzheimer’s, atherosclerosis, schizophrenia, PSP, etc.) are the result of a genetic predisposition and an environmental trigger, with “environment” being broadly defined as anything other than the person’s genome. This study suggests that for PSP, the trigger (or one of the triggers) is something associated with the lifestyles, work places or home neighborhoods of people with lesser education. But the only clue the study provided beyond that is that the trigger may be something in well water. Furthermore, using well water may tend to correlate with other toxic exposures or experiences that the survey did not ask about.
This result may now stimulate researchers to study “environmental” causes of PSP more closely and may induce granting agencies to support such studies. Of course, this search will be guided in part by ongoing genetic studies of PSP: If a variant in a detoxification gene is found to be over-represented in PSP, then perhaps the corresponding toxin is the environmental trigger. If a gene variant that causes over-expression of a gene is found to be over-represented in PSP, then environmental agents that cause a similar effect would immediately become suspect.
Another point, just to make life more complicated: Environmental toxins may not only act directly, as, for example, lead in the drinking water affects childhood brain development. They may also cause epigenetic changes that affect the expression of genes. They may also affect the gut bacteria, the “endobiome,” which itself produces and alters a wide array of compounds, some of which could be pathogenic.
So we’ve got work to do, but Dr. Litvan and colleagues have taken an important step.