The same genetic factors are likely to determine whether certain environmental toxins are quickly eliminated from the body or instead accumulate because enzymes work more slowly. Furthermore, genes may also determine whether an individual is more or less susceptible to nerve cell death once a person has been exposed to a toxin. It is important to note, though, that none of these genes and enzymes would cause the disease unless a person was exposed to the toxin to which these enzymes are responding. This mechanism is what epidemiologists call a gene-environment interaction. When studying the effect of toxins on a disease, it is important to know who is susceptible to the toxin and to look for a human population with a high likelihood for the exposure of interest.
Pesticides are ubiquitous in the environment.
Large volumes of pesticides are being used in agriculture and for public campaigns to control mosquitoes and Med-flies. This is another reason why occupational groups are studied by epidemiologists, since records often exist for chemicals used in certain professions. Some of these record systems even go back quite far in time, which is helpful in assessing long-term exposure. To address the question of whether environmental toxins such as pesticides may cause PD, the UCLA research team plans to conduct an epidemiologic case-control study of newly diagnosed PD patients from three rural Californian counties. The three rural counties targeted by the study are the leading counties for gross value of agricultural production in California.