A single genetic flaw may cause up to five per cent of inherited cases of Parkinson's disease, according to researchers who say the findings could be key to future genetic testing.

The mutation in the gene LRRK2 increases the risk of developing the nervous system disorder, according to three studies published in Tuesday's online issue of The Lancet.

To find the mutation, three teams of researchers in Britain, the U.S. and the Netherlands independently scanned the DNA of people with Parkinson's, a neurodegenerative disorder that affects more than one per cent of people over the age of 65.

Actor Michael J. Fox has promoted awareness of Parkinson's disease. (CP file photo)

Parkinson's disease occurs when nerve cells degenerate in the part of the brain that controls muscle movement. Symptoms include tremors in the hands, arms or legs, poor balance and co-ordination and a stiff walk.

Two of the studies found the mutation in four out of 61 Italian, Brazilian and Portuguese families with a history of Parkinson's.

Among 20 North American families, 35 individuals had the disease.

Finding the mutation link across several populations boosts the confidence scientists place in the results.

Genetic test on horizon

"Mutations in this gene could become the most important cause of disease susceptibility for Parkinson's disease identified so far," said William Nichols, of the Cincinnati Children's Hospital Medical Centre, who led the North American study.

Since researchers have also identified other mutations in the LRRK2 gene, it may become a "a key component of genetic testing for Parkinson's disease in the near future," he said.

PARKINSON'S QUICK FACTS

The LRRK2 gene is on a region of human chromosome 12 called PARK8. The gene encodes a protein named dardarin, named for the Basque word dardara, which means tremor – a major symptom of Parkinson's disease.

The third study on British patients looked at patients with Parkinson's who lacked a family history of the disease.

They found the mutation in eight out of 482 patients, or 1.6 per cent, which suggests the mutation can also occur sporadically.

In sporadic cases with no inherited cause, scientists often suspect exposure to harmful chemicals, radiation or some other environmental factor is the cause.

There is no cure or preventive treatment for Parkinson's, which means currently genetic tests would offer no medical benefit, noted Alexis Brice of France's National Institute for Health and Medical Research.

In a journal commentary accompanying the studies, Brice said it is also important to gain a fuller picture of the genetic causes of the disease, such as if other genes are implicated.

The U.S. National Institute of Neurological Disorders and Stroke is funding an $8-million study designed to identify the genes causing Parkinson's disease.

Some medications can control the symptoms of Parkinson's. Actor Michael J. Fox and boxer Muhammad Ali have the disease.