Two new studies strongly suggest that a mutation in a recently discovered gene is the most common genetic cause of Parkinson's disease identified to date. The discovery by an international research team provides fresh evidence that genetics may contribute to the development of some cases of Parkinson's disease. The findings could lead to the development of a genetic test to detect the mutation in individuals at risk. The research team includes investigators at the National Institute on Aging (NIA) and scientists supported by the National Institute of Neurological Disorders and Stroke (NINDS).

Scientists have long suspected genetics play a role in the onset of the disease. In these studies, the investigators found that a mutation in the gene LRRK2 appears to occur in at least one of every 60 people who have the disease. Overall, the mutation could be responsible for up to 5 per cent of Parkinson's disease in people with a family history of the disorder and may account for 1.5 to 2 per cent of cases in individuals who do not have a family history of the disease. The researchers found a mutation in one copy of the gene can lead to the disease, the release from NIH explains.

"Among the forms of Parkinson's disease that are genetic in origin, this gene mutation causes more cases of Parkinson's disease than any other gene discovered to date," says Andrew Singleton, chief of the Molecular Genetics Unit in the NIA's Laboratory of Neurogenetics. "Knowing that this mutation is not only important in familial forms of disease, but in typical sporadic disease, where there is no strong family history, could lead to earlier detection of Parkinson's disease. Further study of how this gene works also might help scientists identify new treatments," he added.

Singleton and his colleagues recently discovered LRRK2, a gene that encodes a protein named dardarin by the researchers from the Basque word dardara, which means tremor, a major symptom of Parkinson's disease. It was isolated on a region of chromosome 12 called PARK8 by investigators who studied five families with a history of Parkinson's disease who lived in the Basque region of Spain and in England.

In these new studies, the researchers sought to determine the prevalence of the genetic mutation in other families and individuals being studied by the Parkinson's Study Group with NINDS support. In an analysis of 358 families with a history of Parkinson's disease, for instance, the investigators found that 34 of the 767 people who had inherited the disease had at least one copy of the mutated gene. Similarly, the team detected one copy of the mutation in 8 of 482 people with Parkinson's disease, but who didn't report a family history of the disease.

"NINDS is pleased to have supported the collection of this large group of families and sibling pairs, which is proving to be an invaluable resource for these studies, Diane Murphy, a programme director at NINDS says adding,
"Because the prevalence of this mutation is 5 percent in families with a history of the disease and it is relatively common even among those without a family history, it's possible that detecting this mutation will help identify people at increased risk for Parkinson's disease."