Researchers suspect link between welding and Parkinson’s disease
St. Louis, Jan. 22, 2001 — Scientists have identified the first clue
that welding might trigger the early onset of Parkinson’s disease (PD).
A research team led by neurologist Brad A. Racette, M.D., found that 15
professional welders developed typical clinical and neurological signs
of the disease an average of 15 years earlier than the general
population. The study is featured in the January issue of the journal
Neurology with an accompanying editorial.
"This research doesn’t prove that welding causes PD," explains Racette,
an assistant professor of neurology at Washington University School of
Medicine in St. Louis. "But it’s suspicious that the majority of these
patients had a much younger age of onset. Our theory is that we have
identified a group of people who probably would have developed the
disease eventually, but something in the welding environment caused them
to develop symptoms earlier."
PD is a progressive movement disorder that affects more than 1 million
Americans. It is characterized by slowness of movement and tremors that
affect one side more than the other. Although genetics can account for
some cases, 80 percent of PD patients lack a family history of the
disease.
Scientists therefore have hypothesized that environmental factors are
largely responsible. However, no such factors have been identified.
One clue, though, is that manganese miners are susceptible to a
condition called manganism because they inhale large amounts of the
mineral manganese. The disease is classified as a Parkinson syndrome
because it bears a resemblance to PD. But both the symptoms and brain
pathology are significantly different. Welding fumes also
contain high levels of manganese. But when a young welder walked into
Racette’s office and said he was suffering from manganism, Racette knew
something was fishy.
"Manganism is a very different disease. To me, this patient clearly
looked as if he had PD," Racette says.
He soon discovered a lore that welding may lead to PD; material data
safety sheets even list the disease as a possible hazard. But there is
little scientific evidence to back up the idea. Racette and colleagues
therefore set out to determine whether welding is in fact an
environmental contributor to PD. They identified 15 professional
welders among patients in the school’s Movement Disorders Center. Then
they compared the welders’ medical history and clinical symptoms with
those of control PD patients.
They found no clinical differences between the welders and typical PD
patients. The two groups had the same severity and frequency of symptoms
and responded similarly to levodopa, a drug used to treat PD. The only
statistically significant difference was average age of onset: 45 for
the welders or 15 years younger than for the control group.
Racette and colleagues also imaged the brains of two of the welding
patients and 13 control patients. People with PD typically have lower
levels of a neurotransmitter called dopamine in certain regions of their
brain. Using a technique called fluorodopa positron emission tomography
(FDOPA PET), the researchers determined how much dopamine the brain
could take up. With that information, they assessed the extent of
Parkinson-like deterioration. The FDOPA PET scans revealed no
significant difference between the welding and control groups.
Therefore, the welders appeared to have typical PD. "These results are
really exciting because we may soon be able to identify the first
environmental cause of PD," says Racette. "Our first goal is to show
that welding truly does cause this disease. Then we can figure out which
aspect of welding is responsible." This information,
Racette argues, will help determine whether welders should take
precautionary measures and also will help researchers begin to unlock
the underlying cause of this debilitating disorder.
In the editorial that accompanies the paper, Canadian neurologist Ali H.
Rajput, M.B.B.S., F.R.C.P.C., likens the search for environmental causes
of PD to looking for a needle in a haystack. "By narrowing the focus to
one environmental group, Racette et al. have chosen a smaller stack and,
therefore, have a greater chance of finding whether there is a needle or
not," he says.
Contact: Gila Reckess
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314-286-0109
Washington University School of Medicine
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Judith Richards, London, Ontario, Canada
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