Glucocerebrosidase (GBA) mutations are the most common risk factor for Parkinson's Disease (PD). GBA-related PD(GBA-PD) exhibits a more malignant phenotype as compared to no-carriers. Still, the mechanisms behind the increased malignancy in GBA-PD are not well understood. The definition of biomarkers able to stratify PD clinical trajectories in PD is therefore crucial to identify effective treatments and support diagnosis.The investigators will examine the role of GBA-mutations in accelerating a-synuclein (a-syn) and synaptic pathologies in PD by combining neuroimaging (positron emission tomography-PET), biochemical and clinical features. This will illuminate the pathophysiology underlying GBA-mutations in PD and identify biomarkers for the malignant PD phenotype. Also, the investigators will combine longitudinal clinical and imaging/biochemical features to define a prognostic algorithm for predicting disease faster progression in GBA-PD and monitoring disease trajectories in unaffected GBA carriers.