Conclusion
Gene therapy for PD is leading the way in advancing our understanding of this important approach to the treatment of neurodegenerative disorders. Well-characterized viral vectors can be accurately delivered to the relevant brain regions thought to be responsible for the major symptoms of PD. Safety profiles appear favourable, with effects sustained over years and little or no evidence of a resultant immune response to the vector or transgene. Extensive preclinical assessments have led to small scale Phase I and II trials in patients, with both some predictable beneficial outcomes and some unpredictable observations. The need for careful patient selection and monitoring has been highlighted on several occasions, alongside the ethical difficulties with performing truly blinded trials (involving sham surgical procedures). Nonetheless, several therapies appear promising but will require further validation in Phase III trials, with subsequent comparisons with established pharmacological and surgical treatments.