As a result, the quality of infusions is highly variable and the effective coverage observed pre-clinically [1], [2] has been poorly reproduced in clinical trials of glial-derived neurotrophic factor (GDNF) for treating Parkinson’s disease [3] neurturin gene for treating Parkinson’s disease [4], the immunotoxin cintredekin besudotox [5],[6] for treating brain tumors or the chemotherapeutic paclitaxel [7], also for treating brain tumors. The gene discussed is NRTN; the disease is Parkinson disease.