The correlation analysis between serum GDNF levels and abnormal white matter fiber FA values was performed on the PD-MCI group to screen brain regions significantly correlated with changes in serum GDNF levels in PD-MCI patients, and the results showed (Figure 3): in the PD-MCI group, the regions that showed a significant correlation with GDNF levels were the left internal capsule (r = 0.342, P = 0.025), right corpus callosum (r = 0.407, P = 0.018), right cingulate gyrus (r = 0.655, P = 0.001), and left corticospinal tract (r = 0.528, P = 0.006). The gene discussed is GDNF; the disease is Parkinson disease.