Parkinson's is likely to have a genetic component

Parkinson's Disease Society

A team led by Dr. Sigurlaug Sveinbjornsdottir of the National University Hospital in Reykjavik, Iceland studied 772 Icelanders who developed Parkinson's after the age of 50.

They found that the risk of Parkinson's was 6.7 times higher among people who had a brother or sister with the disease.

The risk was 3.2 times greater among people who had a parent who had developed Parkinson's and 2.7 times higher among those who had a niece or nephew with the disease.

Subtle effect

The researchers said the effects of the genetic mutation appear to be subtle, which is why Parkinson's frequently skips generations.

The team found no evidence that spouses were more likely to develop Parkinson's.

This suggests that environmental factors such as exposure to chemicals later in life do not play a role.

But the researchers left open the possibility that environmental factors shared by family members early in life could be a factor.

Writing in the New England Journal of Medicine, they said: "This may indicate a role for some shared environmental factor early in life."

A spokeswoman for the Parkinson's Disease Society told BBC News Online: "Most people now believe that, as with many other common conditions, Parkinson's is likely to have a genetic component which makes some individuals susceptible to something in the environment, perhaps a chemical or a virus.

"However, it does not alter the fact that the risk of the children of people with Parkinson's also developing the condition is negligible."