Parkinson's disease
Heredity and Parkinson's disease
This is a neurological condition which is characterised by a tremor or shaking movement and stiffness in the muscles. Parkinson's disease is a progressive condition and will gradually get worse over time. Parkinson's disease tends to affect older people and the risk of developing the condition increases with age, affecting approximately 1-2 per cent of people aged over 60.
In some cases people with Parkinson's disease have a relative with the condition. If there are 3 or more people in the same family with Parkinson's disease, it is generally accepted that a gene is present which increases the risk of the condition. It is uncommon for Parkinson's disease to be caused by genetic factors and most experts agree that genetic factors are linked to environmental triggers. The exact role genetics plays in sporadic Parkinson's disease is not fully understood.
Genes linked to Parkinson's disease
In 1997 a study was carried out on a large family in Italy. Individual members of the family had Parkinson's disease and this was passed to the child from the parent (dominant inheritance). Researchers discovered the gene that was responsible for Parkinson's disease in the family: it was the gene coded for a protein known as alpha-synuclein. Studies on the brains of people who died from Parkinson's disease show that there are tiny collections of Lewy bodies, which contain a large sum of alpha-synuclein protein. This was the case for both inherited and non-inherited Parkinson's disease. The study confirmed that the protein plays a significant role in Parkinson's disease and further research is being carried out in this area.
Since 1997 four more genes have been identified: they are known as LRRK2, DJ1, PINK1 and Parkin. The first gene listed was found in families with dominant inheritance while the last three genes were discovered in children who had Parkinson's diseases through recessive inheritance (they did not inherit the condition from their parents).
There is evidence to suggest that the genes named above contribute to early-onset Parkinson's disease, which affects people under the age 30. However, further research is needed.
It is believed that at least nine genetic mutations have been identified which increase the risk of Parkinson's disease. Mutations affect the gene's ability to code information which is used by the cells for the body's development and processes. Most genetic experts believe genetic factors are rarely the sole cause of Parkinson's disease and that environmental factors, such as exposure to toxins or chemicals, increase the risk in a person who is already susceptible to the disease.
Who gets Parkinson's disease?
In the majority of cases inheriting a faulty copy of an individual gene does not cause Parkinson's disease. Experts believe a combination of factors, including environmental factors and genetic factors, determine who is affected and when. Research suggests that certain people live their lives with no recognisable symptoms, while others have the condition and have noticeable symptoms. Research into the causes of Parkinson's disease is ongoing.
Genetic testing for Parkinson's disease
Genetic testing is possible for some of the genes associated with Parkinson's disease, including the Parkin gene and the PINK1 gene. It is currently believed that the outcome of testing is only of use for those who develop early-onset Parkinson's disease. Research suggests that PINK1 is an uncommon cause of inherited Parkinson's disease, with genetic mutations of the gene only present in 1-2 per cent of people affected by Parkinson's disease before 30 years of age. Genetic testing may be beneficial for people who have relatives whom have been diagnosed with the condition. They may wish to know if there is a higher risk of them developing the condition or passing it onto future generations.