Parkinson's is not a single condition. Firstly, there are many different causes for what we now call “Parkinson's disease”. Consider, for example, the various genetic causes of parkinsonism. In addition, a distinction can be made between Parkinson's disease and the so-called 'atypical parkinsonisms'. The latter is a collective name for a group of disorders, all of which may be associated with Parkinson's symptoms and thus resemble Parkinson's disease, especially in its early years. However, atypical parkinsonisms have usually another disease course, and often respond to Parkinson's medication differently. Examples of atypical parkinsonisms are Progressive Supranuclear Palsy, Multiple system atrophy, and vascular Parkinsonism.