What causes Parkinson’s disease?

In Parkinson’s disease (PD) there is a lack of a chemical in the brain called dopamine. This is because the brain has lost many of the nerve cells that normally make dopamine. Losing nerve cells is a completely normal process that occurs in even the healthiest person. However, when movement-related signs of PD appear, it indicates that a very large number of the lost cells are from a specific part of the brain called the substantia nigra (see Figure, below). This area is strongly involved with the control of body movement.

In addition, it is thought that nerve loss also occurs in other parts of the brain, producing non-movement related effects, and adding to the large variety of symptoms that can be observed in PD.

Position of the substantia nigra within the brain

(Click on animation to enlarge.)

Medical experts are not yet certain what destroys these nerve cells, or what causes some people to develop PD and not others. However, PD is not an infectious disease and it is not contagious. Medical research is underway to find out about the role that genes play in PD, and whether they could be used as a form of diagnostic test. Current evidence indicates that the development of PD in people below the age of 40 or 50 may be inherited in some families, and further research is ongoing.

It is also possible that the nerve damage in PD may be caused by a factor from the environment. In the past, it was suggested that exposure to harmful chemicals such as pesticides, drinking polluted water, or even a physical factor such as a head injury may cause PD although, at present, there is no evidence to support these suggestions.

The current thought is that although PD itself is not inherited, there is some type of inherited factor (‘in the genes’ or ‘genetic susceptibility’) that makes some people more susceptible to the effects of harmful environmental factors such as those described above – and this may raise their risk of developing PD.