I think that's one of the real success stories in Parkinson research. Had you asked a Parkinson doctor 15 years ago if Parkinson's was inherited, they would have said no. At conferences, some of my senior colleagues were laughed at because they suggested there was a strong genetic component to Parkinson's. Now it turns out there are at least eight different genes that we can currently test for that cause Parkinson's disease.
The trouble is that there's a whole bunch of issues there--i.e., who should we test, why should we test it--but there's no question that there are genes that cause Parkinson's disease that we didn't know about. The first one was discovered in 1997, so this is relatively new information.