Scientists have proved for the first time that gene therapy is an effective treatment for Parkinson's disease, the progressive disorder of the nervous system which causes tremors, delayed movements and rigidity.

Patients who had a gene that controls the chemical responsible for co-ordinating movement put directly into their brains experienced significant improvement in their ability to control their hands, get up and walk.

It is the first time a randomised, double blind trial has demonstrated the effectiveness of the therapy in Parkinson's disease, which affects 120,000 people in the UK.

By replacing defective genes with properly functioning ones, gene therapy could, in theory, correct the basis of many diseases. Moreover, a single treatment should have lifelong effects, removing the need for daily treatment with drugs or regular check-ups.

Scientists said the latest advance demonstrated that the therapy could work for a range of neurological disorders. Professor Adrian Thrasher, president of the British Society of Gene Therapy, said: "It has proved extremely efficacious in blood disorders and in disorders of the retina. Using genes in the treatment of disease does have great potential."

American scientists conducted the trial on 45 patients in the US. Half had burr holes drilled into their skulls and a solution containing the gene, called GAD, and a harmless virus, AAV2, infused into an area of the brain called the subthalamic nucleus.

The AAV2 virus was used to carry the gene into the cells by infecting them. The virus is thought to be safe – more than 80 per cent of the population have been exposed to it and it is not known to cause any disease – but its long-term effects in the brain are not known.

The remaining half of the patients were the control group. They had sham surgery – the burr holes were drilled halfway through their skulls and were washed with catheters carrying saline solution in the same way as the treatment group.

The brain has no sensation and although all the patients in both groups were awake during the procedure, they were unable to tell whether they had received the genuine infusion or the sham version.

The results showed patients who received the gene therapy had twice the improvement in motor control compared with the sham surgery group after six months – an average gain of 23.1 per cent on the Parkinson's rating scale against 12.7 per cent.