Clinical/surgical considerations.

While there are a diverse number of indications for the potential use of cell and gene therapies in people, many of the medical conditions being treated need to consider some general clinical and surgical issues, not only in designing clinical trials, but also in the eventual application of the therapy if shown to be successful. Such issues include the precision of the diagnosis and stage of disease, the presence of significant comorbidity, as well as the challenges that may be encountered in trial designs involving the neurosurgical delivery of these advanced interventions. This chapter discusses details of these issues that have arisen particularly in the field of Parkinson disease and other forms of neurodegeneration, although the general principles and considerations discussed may be equally relevant to other neurologic and nonneurologic conditions.