From transplants to gene therapy for Parkinson's disease.

The efficacy of fetal tissue transplants in the treatment of Parkinson's disease has been demonstrated preliminarily. However, results are short term, and have not been confirmed in prospective randomized controlled trials. Furthermore, although patients are improved, they remain severely disabled. There are several problems with the widespread clinical use of fetal tissue that make the use of molecular biological strategies more compelling. Several conceptual problems are shared by both fetal and molecular biological neuroreconstruction strategies. It is necessary to characterize the "dose" of the transplanted therapeutic agent as well as its volume of distribution. The symptoms that may improve following neuronal reconstruction are likely to be directly related to the somatotopic localization of the transplants; the duration of benefit should be long enough to be relevant in a chronic disease such as Parkinson's disease. Operative therapies that utilize gene therapy or other reconstructive neurosurgical techniques are likely to require novel clinical trial designs to demonstrate their efficacy.