Gene therapy for Parkinson's disease: progress and challenges

Therapy for Parkinson's disease (PD), a common neurological disorder characterized by pathological degeneration of the nigrostriatal dopaminergic system, remains unsatisfactory. Gene therapy is considered one of the most promising approaches to developing a novel effective treatment for PD. Among the numerous candidate genes that have been tested as therapeutic agents, those encoding tyrosine hydroxylase, guanosine triphosphate cyclohydrolase I and aromatic L-amino acid decarboxylase all boost dopamine production, while glial cell line-derived neurotrophic factor promotes the survival of dopaminergic neurons and is generally believed to possess the greatest potential for successful restoration of the dopaminergic system. The genes encoding vesicular monoamine transporter-2 and glutamic acid decarboxylase have also produced therapeutic effects in animal models of PD. Both viral and non-viral vectors, each with its particular advantages and disadvantages, have been used to deliver these genes into the brain. Whether or not regulatable expression systems are essential to successful gene therapy for PD remains a critical issue in the clinical application of this emerging treatment. Here we review the current status of gene therapy for PD, including the application of control systems for transgene expression in the brain.