It has been also reported that downregulation of mRNA [12] and protein [13] of BDNF in the substantia nigra of the postmortem brains of the patients with Parkinson’s disease (PD), one of the progressive neurodegenerative disorders, suggesting that impaired BDNF/TrkB system is involved in the progression of PD symptom. The gene discussed is BDNF; the disease is Parkinson disease.