Is Parkinson's Genetic?
By Heather Maloney
Beth Israel Deaconess Medical Center staff
Approximately 50,000 Americans are diagnosed with Parkinson's disease each year, and many people wonder if they, too, could develop this potentially devastating disorder. A chronic, progressive disease, Parkinson's can cause debilitating symptoms such as tremor, rigidity, balance problems and slowed movement.
One of the issues researchers have been tackling is the degree to which Parkinson's is determined by genetics. The good news is, in most cases, if a family member has the disease, you are still at relatively low risk for developing it.
"If you have an immediate family member with Parkinson's disease, then your risk of developing PD in most cases is about double that of the general population," says
David K. Simon, MD, PhD, a neurologist in the
Parkinson's Disease and Movement Disorders Clinic at
Beth Israel Deaconess Medical Center and an Associate Professor of Neurology at Harvard Medical School. "But that still puts your risk at only about two percent, since about one percent of the population over the age of 65 develops the disease.
"The question of how much of Parkinson's disease is genetic is controversial," adds Dr. Simon. "We don't know precisely what percentage of PD is inherited, but for most people both genetics and environment are likely to be factors."
Scientists have identified several genetic mutations associated with PD. For example, mutations in the LRRK2 gene (usually pronounced "lark-2") cause between one and two percent of all cases of Parkinson's disease, with a higher frequency in individuals with an Ashkenazi Jewish background. But most patients do not have any of these known mutations. For some of these mutations, including the LRRK2 gene mutations, having the mutation increases the risk of PD but doesn't guarantee that a person will develop the disease.
The average age of onset for Parkinson's disease is about 60 years old, although, according to the National Institutes of Health, approximately five to 10 percent of people with PD develop "early-onset" disease that begins before the age of 50. Early-onset forms of the disease seem to be more strongly influenced by genetic factors, and some have been linked to specific gene mutations.
Dr. Simon is careful to point out, however, that environmental factors may be just as important in determining if a patient is at risk. For example, there is some evidence that exercise lowers the risk of PD in men, while data on the impact of fruit and vegetable consumption is mixed.
Dr. Simon also notes that "studies have consistently indicated that increased intake of caffeine is associated with a lower risk for PD." And the list goes on.
"Some studies suggest that recurrent head traumas, such as those suffered by some professional athletes, could put you at risk … there is also discussion about a link between exposure to certain metals and increased risk for PD," he says.
Many factors continue to be studied in an effort to determine what combination of genetics and environment will help doctors pinpoint who is most at risk for developing Parkinson's disease.
"There is some data that suggests that people who have had high exposure to pesticides have a higher rate of PD if they also have a particular genetic variant that makes them susceptible to this effect from pesticide exposure," Dr. Simon says. "So genetic and environmental factors can interact with each other to determine one's risk of PD."
So, bottom line, if you have a family history of Parkinson's, is there any way to tell if you will develop the disease? Not exactly.
One option is genetic testing.
"If you have PD and also have a sibling or parent with PD, then there are certain genetic tests that can be considered, particularly if you or your family members have very early onset PD," Dr. Simon says. But, he cautions, testing will not always provide definite answers, and could cause unnecessary worry.
"Any testing will still leave lots of questions," he says. "And at this point, nothing has been proven to prevent PD or to slow progression of the disease, so it's usually not worthwhile to test someone who hasn't already exhibited some symptoms of the disease."
Above content provided by Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.
Posted July 2012