In postmortem examinations of the brains of controls and patients with PD, in situ hybridization study showed that BDNF mRNA is expressed by dopaminergic neurons in the substantia nigra pars compacta (SNpc) of healthy controls without known neurological disease, but the mRNA expression of SNpc BDNF was reduced in the brain of patients with PD. The gene discussed is BDNF; the disease is nervous system disorder.