The direct cause of Parkinson's disease is the progressive death of nerve cells in an area of the brain called the substantia nigra. These cells produce a chemical called dopamine that helps direct normal movement and activity. Scientists have not determined why these particular cells die, but without dopamine, the activity of other, related brain areas can be substantially altered. Therapy with the drug levodopa and some surgical interventions can temporarily diminish symptoms of the disease. However, they cannot replace the lost brain cells, nor can they stop the progression of the disease.
Gene therapy represents one hope for preventing the loss of the dopamine-producing neurons.
Schulz and his colleagues hypothesized that if they could interfere with a process called apoptosis, or programmed cell death, they might be able to rescue the dopamine neurons. They focused their effort on a group of molecules called caspases, which help to carry out apoptosis. Their experimental approach was to insert the gene for a caspase inhibitor into the genetic material of a benign virus. This virus was then surgically injected into the brain, where it incorporated its genetic material into the chromosomes of the dopamine neurons. The neurons did the rest, producing caspase inhibiting proteins from the foreign gene code.