The numbers of proliferating cell nuclear antigen- (PCNA-) positive adult NSCs in the SVZ and nestin-positive precursor cells in the OB are decreased in the PD-affected postmortem brain, and a decrease in NSCs correlates with the progression of PD, while L-Dopa treatment appears to increase NSC numbers [44, 45]. The gene discussed is PCNA; the disease is Parkinson disease.