Washington: Scientists claim to have identified at least two genes linked to Parkinson's disease, a finding which may pave the way for better treatments for the second most prevalent neurological condition after dementia.

A team, led by Neuroscience Research Australia, says the two genes are related to protein accumulation in the brains of people with Parkinson's disease and can indicate how quickly the disease will progress in a person.

"Our study shows that these two genes can be used as a surrogate marker to estimate the rate of Parkinson's disease progression, with positive predictive values of 94 to 100 per cent for certain genotypes.

"This finding could be important for guiding the development of therapies for Parkinson's disease," said Dr Yue Huang, who led the team.

Parkinson's disease is characterised by the abnormal accumulation in the brain of a protein called ?-synuclein, as well as the loss of dopamine-producing cells in an area of the brain known as the substantia nigra.

The loss of these cells causes the symptoms of Parkinson's, including trembling, stiffness, slowness of movement and a loss of fine motor control.

In their research, published in the 'Journal of Parkinson's Disease', the scientists investigated two genes -- NACP and MAPT -- implicated in other studies as risk factors for Parkinson's disease. The NACP gene is related to the production of the synuclein protein in the brain, while the MAPT gene is involved in the production of another protein in the brain, called tau.

By testing 123 patients with Parkinson's to determine what version of NACP and MAPT they carried, and measuring the severity of their disease and how quickly it progressed, the team was able to demonstrate that certain versions (polymorphisms) of these genes interact to influence how quickly some patients with Parkinson's deteriorate.

The scientists found that those people with a variation of the NACP gene that predisposed them to producing high levels of the synuclein protein in the brain experienced more rapid disease progression.

They also found, however, that patients who had low levels of ?-synuclein, but a variation of the MAPT gene that meant they produced high levels of the tau protein, also experienced more rapid disease progression, a release said.

Dr Huang said: "Based on current knowledge, it is perhaps not surprising that genetic variation predisposing to high synuclein expression gives rise to more rapid progression of Parkinson's disease.

"However, our results suggest that low synuclein expression may also be as detrimental in people with high tau expression levels, calling into question the concept that reducing neuronal synuclein in all Parkinson's patients may be therapeutically advantageous."