Parkinson’s disease (PD)—a complex, progressive, and incurable disorder—affects at least 500,000 people in the United States. Caused by degeneration of nerve cells in the brain, Parkinson’s is the second most common neurodegenerative disease in the United States, after Alzheimer's disease. Its symptoms—significant tremors and shaking, stiffness, impaired movement–often interfere with daily life.

No blood or laboratory tests have been available to diagnose PD, but a recently discovered genetic mutation will significantly improve future PD genetic testing and counseling. Researchers in a collaborative Parkinson Disease Study group report that a mutation on the LRRK2 gene is responsible for 5 percent of individuals with familial, or inherited, Parkinson’s disease.

Tatiana Foroud, associate professor of medical and molecular genetics at the Indiana University School of Medicine and principal investigator for the multi-site study, says the discovery has broad implications for genetic screening for the disease.

“Our results suggest that the mutation we have studied is the most common cause of Parkinson’s disease identified to date,” says Foroud. “While a great deal of work remains to be done, it is clear that any future genetic testing for Parkinson’s disease must include studies of the LRRK2 gene.”

The multi-site study under the Foroud’s direction is funded by an $8 million grant for the National Institute of Neurological Disorders and Stroke. Foroud and others reported their recent findings in The Lancet. The IU portion of the study focused on 767 Parkinson’s disease patients from 358 families.

Foroud, also a primary investigator at the IU School of Medicine’s Stark Neurosciences Research Institute, is involved in numerous studies aiming to map genes that contribute to common genetic disorders such as Parkinson’s disease, Alzheimer’s disease, bipolar disorder, and alcoholism. Her studies often include the recruitment of families afflicted with these disorders, followed by molecular analyses to detect genetic linkage to particular chromosomal regions. Foroud’s goal is to identify genetic variants that may determine susceptibility to diseases such as alcoholism and PD as well as protect individuals from the disorders.