PDCD6 and Parkinson disease: As an example, PDCD6, a top common correlating protein between G2019S and R1441G (ρ = −0.75, P = 5.51 × 10−10), participates in vesicle trafficking, mediates mitochondrial cytochrome c release and apoptosis,54 and has been linked to PD.55 In summary, although correlation does not mean causality, differential phospho-/proteins at the 18-feature G2019S classifier are associated with disease severity, therefore holding clinical interest.