Parkinson's Risk Higher for Men
Theory suggests moms more likely to pass illness on to sons
THURSDAY, March 18, 2004 (HealthDayNews) -- A review of multinational studies dating back 24 years appears to confirm what experts have long suspected: Men face a much higher chance of developing Parkinson's disease compared to women.
"This has been something that everyone has assumed for a while, but whenever you stand up and say it someone will say, 'There's no proof of that.' Well, now we've got the closest thing there is to proof," says Dr. Fred Wooten, chairman of the neurology department at the University of Virginia School of Medicine in Charlottesville.
According to Wooten, the most likely culprit for a 'gender gap' for Parkinson's may be the heightened vulnerability of male offspring to a genetic mutation passed down by their mothers.
The study appears in the March 17 issue of the Journal of Neurology, Neurosurgery and Psychiatry.
Parkinson's disease involves the steady loss of brain cells that produce dopamine, a chemical messenger essential to proper motor function. As the levels of dopamine decrease, chemical messages between brain cells "misfire," triggering symptoms such as tremors, loss of balance, rigidity and other abnormalities. Parkinson's is progressive and has no cure, although the use of certain drugs can ease its symptoms. The National Parkinson's Foundation estimates that 1.5 million Americans are affected with the disease.
According to Wooten, the observation that Parkinson's affects more men than women has a long history. "In the original description in 1807 by James Parkinson, he describes five men [and no women]," Wooten points out. "So from the absolute beginning of the descriptions there's always been the sense that there are more men than women affected."
Still, no one had pulled together the data to prove this gender bias until now.
In their study, Wooten's team examined data from seven population-based studies conducted in the United States, China and four European countries since 1980.
They report that, worldwide, males face a 50 percent higher risk of developing Parkinson's than do females.
Uncovering the reasons behind this trend may be a tougher problem, however. There is "weak" evidence that something about the male lifestyle -- increased exposure to pesticides, for example, or a higher incidence of head injury -- might account for men's higher incidence of Parkinson's disease, Wooten says.
A second theory holds that estrogen might help protect women against neurological illnesses such as Parkinson's. "There's a great deal of evidence, both from test-tube studies as well as some animal studies, that estrogen has a neuroprotective role and that higher levels of estrogen in women might somehow protect them from this particular neurodegenerative disease," Wooten explains.
But more intriguing theories focus on the genetics of men -- and their mothers.
First of all, genetic mutations specific to Parkinson's have recently been located on the X chromosome. "Genetic abnormalities on the X chromosome tend to affect men more than women," he says, "because men have only one X chromosome and women have two," leaving men less leeway whenever X-chromosome genes are expressed.
Men might also be more vulnerable to a Parkinson's-linked mutation of a gene found in what's known as mitochondrial DNA. Mitochondrial DNA is a relatively tiny reservoir of DNA found outside the nucleus, and it is only passed via the mother to her offspring.
For reasons that remain unclear, the sons of women who carry this mitochondrial abnormality could be at especially high risk of developing the disease.
"We are about to publish another large, more definitive [study], showing that there's an unexpected excess of maternal transmission in Parkinson's disease," Wooten explains. "If you look at a group of patients affected with Parkinson's disease, and you ask how many of them have an affected mother and how many of them have an affected father, the incidence of affected mothers is higher."
Parkinson's is not the only brain disease more likely to hit men than women. "Diseases like amyotrophic lateral sclerosis -- ALS, or Lou Gehrig's disease -- are more common in men," says Dr. Jay Van Gerpen, director of the Movement Disorder Clinic, part of the Ochsner Clinic in New Orleans. He also notes tremor-type illnesses similar to Parkinson's appear to affect more men than women, too.
Can anything reduce your risk for Parkinson's? Van Gerpen says the only lifestyle factors known to decrease disease risk at this point in time are coffee-drinking and smoking.
While no one is advocating smoking, a cup or two of coffee per day might be beneficial, Van Gerpen says. "There have been a number of studies that have shown this -- that patients who consume coffee are less likely to get Parkinson's disease. As a coffee drinker myself, that's good news."
To learn more about Parkinson's disease and available treatments, visit the National Parkinson Foundation or the National Institute of Neurological Disorders and Stroke.