There is no hard evidence that Parkinson's disease is hereditary except in vary very rare forms of the disease (up to 5%).

The latest research shows that some genes may make some people more susceptibility to be likely to develop Parkinson's disease, but this research shows these people would also need to be exposed to environmental toxins or viruses to actually devlop the disease if they have the certain genes. This demonstrates that the chances of this are rare.

At present there is no genetic test freely available for the gene that may make people slightly more suceptable to  Parkinson's disease.

The role genetics may play in the development of Parkinson's disease is currently the subject of much research.