Further serum biomarkers have a less validated use in clinical practice: some authors reported that platelet derived grow factor BB (PDGF-BB) and transforming growth factor β1 (TGF-β1) concentrations are significantly lower in PD patients compared to the control group and serum; conversely, platelet derived grow factor AA (PDGF-AA) and connective tissue growth factor (CTGF) values are significantly higher compared to control samples. Here, CCN2 is linked to Parkinson disease.