POLG and Parkinson disease: Specifically, 34 of the 57 genes (59.65%) including six PD-causing genes (LRRK2, SNCA, UCH1, DNAJC13, SYNJ1, POLG) had higher expression levels in excitatory neurons than in inhibitory neurons (Figure 2), whereas the other 23 genes (40.35%) including five PD-causing genes (ATP13A2, TMEM230, EIF4G1, GIGYF2, FBXO7) exhibited the opposite features (Figure 2).