For example, off target side effects such as aberrant sprouting and weight loss have been reported with long term viral vector delivery of glial cell line-derived neurotrophic factor (GDNF) (Georgievska et al., 2002; Manfredsson et al., 2009; Su et al., 2009) and may limit its effectiveness for application to Parkinson’s disease and other disorders, leading to efforts to develop inducible GDNF vector systems (Chtarto et al., 2016). This evidence concerns the gene GDNF and Parkinson disease.