Parkinson's gene therapy trial success

A US study, published in the journal Proceedings of the National Academy of Sciences, reported that brain scans of 12 Parkinson's patients treated with experimental gene therapy show that the treatment normalises brain function.

A study published earlier this year reported that the symptoms of the same 12 patients had improved markedly without experiencing side effects a year after treatment; however, since all twelve patients received the therapy, there was doubt as to how much of this was down to a so-called 'placebo effect'. But the new data obtained by carrying out 'PET (Positron Emission Tomography) scans' on the brains of the 12 patients confirms that physical changes in the brain did occur, suggesting that the improvements reported by patients were genuine.

Having this information from a PET scan allows us to know that what we are seeing is real,' said lead researcher Dr David Eidelberg. 'This study demonstrates that PET scanning can be a valuable marker in testing novel therapies for Parkinson's disease'.

According to statistics published by the UK Parkinson's Disease Society, 10,000 people are diagnosed with Parkinson's in the UK each year; mostly those aged over 50. Symptoms of the disease, predominantly tremors and impaired movement, result when production of the brain chemical gamma (γ)-aminobutyric acid (GABA) drops, triggering a key area of the brain for the control of movement - the subthalmic nucleus (STN) - to over-activate.

To counteract this, the gene therapy uses a disabled virus, called an adeno-associated virus, to 'infect' the cells of the STN with a corrective stretch of genetic code, which triggers production of the enzyme GAD helping to restore GABA levels. Partly as a safety measure, the gene therapy was only delivered to one side of the brain allowing the other to act as a control.

The PET scans, carried out before the surgery and also six and 12 months thereafter, indicated that the gene therapy improved the region of the brain associated with motor function without interfering with the region associated with cognitive processes. They also showed that the effect of the gene therapy lasted longest in those given a higher dose.

Dr Kieran Breen, of the Parkinson's Disease Society, told the BBC that the disease was likely to be caused by a combination of genetic and environmental factors. 'Because of this, there are many potential ways to treat or cure Parkinson's, and gene therapy is one potential route holding a lot of promise', he said.

The purpose of this phase 1 trial was to test the safety of the gene therapy, however a larger phase 2 trials aimed at assessing efficacy is planned for next year.