There is extensive evidence that blood biomarkers—including the neurotrophins brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), insulin-like growth factor-1 (IGF-1), irisin, and vascular endothelial growth factor A (VEGF-A)—can potentially predict recovery and forecast rehabilitation outcomes in patients with neurological diseases. This evidence concerns the gene GDNF and nervous system disorder.