Men are twice as likely as women to develop Parkinson's disease, Italian researchers suggest.

However, an American expert says while the degenerative nerve condition is more common in men, the difference is not nearly as great as the Italian researchers report in the latest issue of the journal Neurology.

Parkinson's disease occurs when cells that produce the messenger chemical dopamine in a brain area, called the substantia nigra, die or become impaired. Without dopamine, nerve cells fire out of control, leaving patients unable to control their movements.

The progressive disease affects nearly 1.5 million Americans, including U.S. Attorney General Janet Reno, evangelist Billy Graham and actor Michael J. Fox. The four main symptoms of Parkinson's are trembling in the hands, arms, legs, jaw and face; stiffness of the limbs and trunk; slowness of movement and impaired balance and coordination. The symptoms can lead to difficulty walking, talking or completing other simple tasks. While the disease is not fatal, and drug therapies and surgery can help some patients, it has no known cure.

The latest study followed a group of 4,341 men and women, ages 65 to 84, who were part of the Italian Longitudinal Study on Aging. Participants were first contacted between 1992 and 1993 and again three years later.

In those three years, 29 men developed Parkinson's disease, compared with 13 women. Another 14 men and 12 women developed Parkinson's-like symptoms resulting from other neurological causes, such as dementia, drugs or stroke.

After adjusting for age, lead author Dr. Marzia Baldereschi and her colleagues calculated that men were 2.13 times more likely to develop Parkinson's disease than women.

"I think this male predominance is very important," says Baldereschi, a researcher at the Italian National Research Council in Florence, Italy. While her team has several theories to explain the finding, Baldereschi says it's too early to draw reliable conclusions. "There is probably something related to lifestyle, such as occupational exposures," like pesticides, she says.

"It could be also something genetic that could increase the susceptibility to other environmental risk factors to Parkinson's disease," says Baldereschi. "I think that gene-environment interaction is the main avenue for research in this field."

One common theory suggests that higher estrogen levels in women may somehow protect against nerve decay. "This might partially explain while males are at a greater risk of neurodegenerative diseases, but this is true only for Parkinson's disease," says Baldereschi, pointing out that Alzheimer's disease is more common in women.

But the Italian findings raised the eyebrows of at least one Parkinson's expert who says other studies have found that the real-world breakdown of Parkinson's patients is closer to 55 percent men and 45 percent women.

"Even though Parkinson's is a disease of the elderly, this male-female ratio holds," says Dr. Abraham Lieberman, medical director of the National Parkinson Foundation in Miami, Fla.

"It's not a striking difference, but to say that there's twice the risk -- that's stretching things statistically, because there certainly aren't twice as many men as women with Parkinson's disease," says Lieberman.

(From HealthScout)