A woman with Parkinson's disease can write for the first time in 15 years after receiving gene therapy developed by an Oxford company.

Sheila Roy, 57, is one of only 15 people worldwide to undergo the treatment developed by Oxford Biomedica, which involves injecting corrective genes into the brain. She has had the disease for 17 years, and now has severe tremors and loss of balance, making simple tasks like writing impossible.

Mrs Roy is taking part in an early-stage study focusing mainly on dosing and safety. Unlike conventional tablets, the therapy involves just one treatment that does not have to be repeated.

Mrs Roy, from Bedfordshire, says she is now starting to see "a glimmer" of the person she was before her illness.

She said: "Early in 2011 I was rapidly deteriorating. My medication was being less effective, there was increased involuntary movement, where I frequently hit myself but also other people, and had a four second switch from extreme movement to being 'off' and very still."

She added: "You lose confidence, dignity and hope. The ProSavin experience has restored my confidence, enabled better motor function and has given me hope. I can function more normally and, for the first time in 15 years, I can write."

Mrs Roy and five other patients in the UK received a high dose "enhanced" treatment. Over three months, all 15 patients showed an average 29 per cent improvement in motor function.

Biomedica's share price leapt 40 per cent after the results were released. The company employs 58 staff at the science park and 25 staff in Cowley, where it is setting up a manufacturing facility, due to open later this year.

The treatment, using a modified virus to carry the genes, was based on research by Biomedica's founders, Oxford professors Sue and Alan Kingsman.

ProSavin contains genes providing coded instructions for proteins to make dopamine, a brain chemical needed to control movement. Lack of dopamine leads to tremor, stiffness and poor balance.

As well as Addenbrooke's, the trial is at the Henri Mondor Hospital in Paris.

Dr Philip Buttery, from the Cambridge Centre for Brain Repair, who is leading the British arm, said although the research was still at an early stage, the treatment appeared to be having positive results.

More studies involving hundreds of patients will be needed to confirm that the therapy is safe and effective. It could be five years or more before the treatment can be marketed.

Dr Kieran Breen, of charity Parkinson's UK, said: "In addition to ProSavin, there are three other gene therapy trials under way at the moment. So far all the therapies appear to be safe — now the challenge is to see whether they are more effective than the medications we already have."