Furthermore, the inherited gene variations seem particularly to protect white women, which may help explain why Parkinson's disease is seen more often in men.
The study, published in the April issue of the American Journal of Human Genetics and available on-line at the journal's Web site (http://www.journals.uchicago.edu/AJHG/journal/issues/v72n4/024579/024579.html) is the first to assign specific genetic risk factors to the most common form of Parkinson's disease, which affects more than 1 million people in the United States.
The genetic risk factors for Parkinson's disease have been difficult to study because it is a complex disease that likely has both genetic and environmental components, said Jeffery Vance, M.D., lead author of the study. "We are finding that Parkinson's disease is not one disease; it is many diseases," he added.
The disease itself is a degenerative disorder of the portion of the brain that controls movement. Progressive nerve degeneration results in difficulty initiating movements such as walking, a loss of balance, rigidity and tremor.
Recent scientific studies had shown that people affected by Parkinson's disease have defects in mitochondria, the cellular components that produce energy for the body. Studies in rats have shown that chronic exposure to the common pesticide rotenone can cause damage to the energy producing proteins in the mitochondria and induce symptoms that mimic Parkinson's disease in people. These proteins, which together are called complex I, are among the few genes encoded in the genetic material of the mitochondria itself.