In some families, Parkinson's disease appears to run in families and be clearly inherited. Most often these are ‘early-onset’ forms of PD cases where the disease begins earlier in life than usual, although there are also families with late-onset more classic Parkinson's disease as well. Heritable forms of PD account, however, for less than 10% of all cases of PD. Genetics however likely plays an important role in all forms of Parkinson's disease. These genetic alternations typically merely increase risk but they do not inevitably cause the onset of the disease. If you have a first degree relative with the disease, it does not mean that you will inevitably get the disease, too, but you may be at slightly higher risk that someone who did not have a relative with Parkinson's disease. Conversely if you have the disease, it does not mean that any of your children or grandchildren will get the disease. It merely indicates their risk for getting the disease is slightly higher than families without PD. For those patients with multiple affected individuals and a clear inheritance pattern, there is available commercial testing for the identified genetic alterations.