Although correlation does not imply causality, 55% of the signature features were correlated with PD motor severity as determined by UPDRS-III scores, including pSer106 RAB12, pSer2015 MON2, ATIC, PDCD6, RAB9A, PSMC5, LAMP1, HSD13B10, ARHGAP45, NDUFB8 and SCLY. This evidence concerns the gene RAB9A and Parkinson disease.