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>Hi Claire-- the info about your friend is very interesting. There are many >folks who feel that their PD was "caused" or at least "triggered" by toxic >exposure. Every psychiatrist and psychologist learns about the tendency of human beings, when diagnosed with an incurable disease, to firstly enter into denial, ie, "The doctor must be wrong; I *can't* have xyz!" When the diagnosis is confirmed, and the afflicted person finally accepts the diagnosis, they then commonly look for a "cause" for the complaint. This attitude partly comes from a desire to look for someone or something one can 'blame' for the disorder. Another factor is a general disinclination to accept 'bad happenings' as being attributable to 'blind chance'; it just doesn't seem fair. It is generally accepted that by the time PD is diagnosed, 80% of the cells in the substantia nigra have been destroyed. Given that this is so, the time of contracting PD must rest some distance into the past. Therefore, no recent experience or event would be the causative factor. Any proposed causative factor for Parkinson's Disease must take into account the time period over which PD has been definitely known to science, and, to a lesser extent, the cases of PD which have been postulated in history. These include "the man taken with the palsy", mentioned in the Christian bible, the model for the Good Samaratin in Rembrandt's painting of the same name, the suggestion that the model for Leonardo da Vinci's Mona Lisa had PD, and some evidence that may indicate that even one or more of the ancient Pharaohs had PD. That is not to say that a chemical or chemical composition present in today's environment could not be implicated in PD, since it didn't exist earlier in history. Take the case of lead poisoning. It has been postulated that the lead compounds in modern petrol (gasoline) cause disorders in susceptible persons, particularly children. Since gasoline is a recent development, and since cases of lead poisoning were known in in Ancient Roman times, in the Middle Ages, and in the 18th century, it would be tempting to suggest that lead was not the cause. However, one finds that lead water pipes were used extensively in the homes of rich Ancient Romans (that is where the word plumbing comes from - the Latin for lead is plumbum - and you thought it meant someone with a fruit shaped bottom, didn't you!) Then one finds that lead was a component of pewter, commonly used for eating-platters and tankards in the middle ages, and was included as a part of a white pigment in some 18th century paints, then the connection of the disorder with lead is re-established. A theory current among some researchers is that the causes of PD are multifold, and that only the resultant effects are common. Another possibility is genetic heredity; although not everyone with PD has blood ancestors with diagnosed PD. Of course, some diseases with proven genetic connections are known to skip generations. Further, in past times people with PD may well have died before the gross symptoms became apparent. Researchers, being only human, can jump to wrong conclusions. This is usually because they have not made a distinction between cause and effect, or because they were pursuing a theory and accepted the first apparent 'proof' that came along. For example, post-mortem studies of brains from people with PD show a marked incidence of inorganic iron, and an insufficiency of the substance that turns such iron into a form acceptable to human metabolism. Does this mean that PD is caused by inorganic iron in the brain? Or by a lack of chelating agents? Or are both merely a result of PD? This would require a further study to be made to investigate each of these possibilities. For a factor to be considered as a sole cause of PD, some evidence must be adduced that this factor is present in ALL persons with PD, and that it is not present, or is inactive, in control subjects without PD. The fact that no reputable researcher to date has been able to establish such a case for any factor is the reason why some scientists lean to a theory of multiple causes. A common error is to suppose that because a substance or a physiological sign is apparent in every case of PD, that this is proof that the thing found is either a cause of, or as a result of, PD. The researcher needs to examine a 'control group' of people of similar age, weight, lifestyle, ethnicity, etc, to establish a 'norm' against which the PD incidence can be measured. For example, if I told you that excess iron was found in the brains of PD sufferers, and that iron was found in the red blood cells of all persons with PD, would this prove that iron was a causative factor for PD? No, not when you realise that iron is found in the red blood cells of every human being, not to mention all other red-blooded animal life. So research scientists who are attracted to research the causes of PD by the potential for funding as a result of the Udall Bill, or for just plain old-fashioned concern for an afflicted portion of the population, will have to carefully construct their experiments so as to eliminate such potential errors as described above. Jim Slattery [log in to unmask]