A revolutionary technique for inserting healthy genes into unhealthy organs is to be extended to treat childhood blindness and Parkinson's disease.
British scientists are to pioneer the development of gene therapy for chronic and incurable conditions by announcing the first clinical trials on the eye and brain beginning next year.
Professor Robin Ali, head of the gene therapy team at the Institute of Ophthalmology, University College London, said animal tests had shown the approach could lead to an effective treatment for inherited blindness in children and visual deterioration in the elderly.
"There are lots of disorders of the eye that may be very amenable to this sort of novel treatment. There are a lot of eye diseases at present that are not effectively treated, or not treated at all," Professor Ali said. "We and a number of groups around the world have demonstrated proof of principle in a range of animals models for a variety of conditions. So we are now at the stage of seriously considering [clinical] trials."
A second team of scientists is preparing for gene therapy on patients suffering from advanced Parkinson's disease, which is caused by the degeneration of cells in the brain that produce the neurotransmitter dopamine.
Professor Alan Kingsman of Oxford University said he hoped to recruit 10 patients with an advanced disease for a trial to begin early next year. He has set up company called Oxford Biomedica to develop the research. "We have a product that turns cells that don't make dopamine into cells that do. You simply recreate the factory for dopamine. It works extremely well in animal models," Professor Kingsman said.
Gene therapy involves the creation of an artificial human gene that is inserted into the cells of the body by a "vector", which is usually a genetically engineered virus that has been rendered safe. "In Parkinson's, you effectively lose your dopamine factory. What you can do with gene therapy is essentially to deliver the genes that programme cells to make dopamine," he said.
Although initial gene therapy trials on other disorders proved unsuccessful, scientists have recently announced that they have worked well in treating some conditions, notably in babies born with defective immune systems. Now medical researchers want to extend the technique to include not just inherited diseases caused by defective genes, but disorders of later life that have proved difficult to treat by more conventional approaches.
Professor Ali said two trials were being planned, one to treat age-related macular degeneration, when the growth of blood vessels in the eye causes gradual blindness in the over-60s, and inherited blindness in children caused by a defect in a gene resulting in retinitis pigmentosa.
"In the main, to treat the inherited disorder we need to correct the underlying genetic defect, in the case of retinitis pigmentosa, perhaps putting the missing gene back into the photoreceptor cell," Professor Ali said. "Whereas in the case of more complex diseases of the elderly, the approach is usually to try to ameliorate some prominent feature of the disease without treating the underlying genetic defect."
"The major prerequisites for clinical trials have now been established so we can achieve very efficient gene transfer to the eye and achieve life-long gene expression without doing anything toxic. The potential outcome - and we'll have to wait to see whether it is borne out - would be improved night vision and improved peripheral vision. We would be able to determine this very quickly, within a few weeks of treatment."
Professor Ali said a key consideration was to assess the potential benefits of gene therapy compared with the risk of a child losing what little vision he or she may have.
"There is no way we'd undertake a clinical trial if we thought we were seriously risking a child's residual sight," he said.