FGF21 and Parkinson disease: The principal compoent analysis (PCA) showed that FGF21 and PD mice could be separated in a PCA score plot produced from the midbrain (Figure 2B), whereas the FGF21 treated mice could not be distinguished from CON mice, especially along the first principal component PC1 (With PC1 and PC2 accounted for 32.0% and 25.6% of the total variance, respectively, Figure 2B).