The discovery experiment, which included samples from 21 healthy individuals (control), 13 healthy individuals with G2019S mutation in the LRRK2 gene (non-manifesting carrier/NMC), 28 PD individuals without G2019S mutation (idiopathic PD/iPD), and 20 PD individuals with G2019S mutation (LRRK2 PD), were randomly divided into two groups: 70% training set and 30% test set for biomarker selection and predictive ability estimation (Fig. 1, Table 2 for HC, NMC, iPD, and LRRK2 PD patient distributions). Here, LRRK2 is linked to Parkinson disease.