Parkinson’s is a disease of the central nervous system caused by the loss of dopamine-producing cells in the brain. However, exactly why dopamine-producing cells become lost is unclear. Research suggests that a combination of genetic and environmental factors may be responsible. How these two factors interact varies from person to person. It is also unclear why some people develop the disease but not others.

It is rare for Parkinson’s to be passed from parent to child. However, in recent years a number of cases have been identified in which Parkinson’s seems to be at least partly genetic. In these cases, a mutated gene appears to have passed from one generation to the next, and Parkinson’s has developed in several people in the same family.

Genes are segments of the molecule DNA within the nucleus of cells that pass characteristics from parents to their offspring. Scientists believe certain genes may play a role in the genetic causes of Parkinson’s. These genes are an important focus for research. In the future, increased understanding of how such genes may affect the underlying risk, onset (start), and progression of Parkinson’s could be important for future treatments.

It is important to point out that even if an abnormal gene is present and so the risk of developing Parkinson’s is higher, the chances of this happening are still very low.

Some evidence suggests that environmental factors, including toxic chemicals, viruses, bacteria, and heavy metals, may cause dopamine-producing neurons to die, leading to the development of Parkinson’s.

In particular, there has been much speculation about a link between the use of herbicides and pesticides and the development of Parkinson’s.

In the early 1980s, a small number of drug users in California mistakenly took heroin that had been contaminated with a dangerous synthetic drug called MPTP. Anyone who took the contaminated heroin developed very severe and irreversible Parkinson’s-type symptoms almost immediately.

This unfortunate incident has led to significant scientific advances. MPTP has since been used widely in basic research and has helped scientists to learn much more about Parkinson’s.

Scientists currently believe that, in most cases, genetic and environmental factors interact to cause Parkinson’s disease. The extent to which each factor is involved varies from person to person. Unfortunately, it is generally impossible to find out exactly what caused a person to develop Parkinson’s.

While many people with Parkinson’s report one or more family members with the disease, it is not always clear whether one or several genes are the cause.

On the other hand, while some patients suspect that exposure to a chemical or environmental toxin caused their Parkinson’s disease, this is very hard to prove. Active research into the causes of Parkinson’s continues every day.

The single biggest risk factor for Parkinson’s is age. Most people are over 60 when they develop the condition. However, 12-15% are under 45. Men have a slightly higher risk than women.

A number of studies have highlighted factors that are linked to either greater or lesser risk of Parkinson’s. For example, severe head injury and pesticide exposure have been associated with higher risk, while smoking and caffeine consumption have been linked to lower risk. Such studies are not conclusive, but they do highlight areas where further research may help scientists to develop risk-prevention or treatment strategies.

Content last reviewed: March 2021

We would like to thank Prof Carlo Colosimo (Università La Sapienza, Rome, Italy) for his help in reviewing this infomation.

• Rates of Parkinson’s disease are exploding. A common chemical may be to blame – read article on The Guardian
• Parkinson’s disease: alpha-synuclein, a major factor? – Video produced by France Parkinson
• Navigating Clinical Trials – A Guide for Parkinson’s Patients and Families (The Michael J. Fox Foundation), pp. 29-39: Genetics and Parkinson’s Research

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