most Parkinsons cases are environmental

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Most Parkinson's cases not inherited, study finds

Associated Press

By BRENDA C. COLEMAN

CHICAGO, January 26, 1999

Most cases of Parkinson's disease are not the result of a genetic defect

but are instead caused by factors that are probably environmental,

according to a landmark study of more than 17,000 twins.

" For the first time, today we can say that for people with Parkinson's

disease diagnosed after age 50, it's most commonly caused by

environmental factors, " said Dr. Caroline M. Tanner of the Parkinson's

Institute in Sunnyvale, Calif., who led the study. It is published in

Wednesday's Journal of the American Medical Association.

The environmental factors are unknown but may include chemical

exposures, diet and smoking - the last of which paradoxically seems to

lessen the risk of developing Parkinson's, she added in a teleconference

call Tuesday.

A genetic cause is most common in the approximately 10 percent of people

with the disease who are diagnosed before age 50, she said.

At least 1 million Americans have Parkinson's, Tanner said, making it

second only to Alzheimer's disease in frequency as a degenerative

disease of the brain and nerves.

Parkinson causes slow deterioration of the nerves' ability to control

the muscles. It usually starts with small tremors, then progresses to a

shuffling gait and increasing weakness. There is no cure, and drug

therapy tends to lose effectiveness over time.

In 1997, researchers identified a long-sought gene defect that can cause

a form of Parkinson's, but the proportion of cases arising from the

defect was unknown before this study.

In the new study, researchers tracked down more than 17,000 men enrolled

in a World War II-era twin registry. The researchers found 161 twin

pairs in which at least one brother had Parkinson's disease and data on

the pairs was complete.

Among the 161 sets, there were 16 in which Parkinson's had struck before

age 50.

Of the four sets of identical twins, who have exactly the same genetic

material, both brothers had Parkinson's.

Among the 12 fraternal pairs, who share only half their genetic

material, there were only two in which both brothers had Parkinson's.

Researchers calculated that if one twin developed the disease by age 50,

the other was six times more likely to get it if he were an identical

twin than if he were a fraternal twin.

Tanner said environmental factors most likely to play a role in typical

Parkinson's include exposure to chemicals such as pesticides and

herbicides, diet and tobacco smoking. The apparent protective effect of

smoking was found in the twins and in previous research, Tanner said.

She and J. Langston, president of the Parkinson's Institute and

senior author, said the protection is probably real, perhaps caused by

smoking's stimulation of the liver to produce enzymes that neutralize

some toxin that would otherwise provoke Parkinson's.

" But there are about 2,000 chemicals in cigarette smoke, so we still

have a big job ahead of us in finding what chemicals might actually be

protective, " Langston said. " And we don't recommend smoking to prevent

Parkinson's disease. "

An expert not involved in the study said it presents a compelling reason

to search for better treatments, since the drugs now available may

lessen symptoms but don't really attack the disease or prevent

disability.

And surgery is promising but still largely experimental, noted Dr.

L. Cummings of the University of California, Los Angeles. In an

editorial accompanying the study, he recommended that the new findings

should refocus research on environmental triggers for typical

Parkinson's disease and genetic influences in early-onset disease.

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Another important medical discovery that was delayed for decades by

focusing on laboratory research with mice and other animal models.

Andy

*Peace and Light*