To investigate the prevalence and clinical feature(s) of Parkinson's disease (PD) patients with expanded (ATXN2 and MJD1) genes of spinocerebellar ataxia type 2 and 3 (SCA2 and SCA3/MJD) in a mainland Chinese population, CAG triplet repeat expansions of (SCA2 and SCA3/MJD) genes (ATXN2 and MJD1) were analyzed in a cohort of 452 PD patients, including 386 sporadic and 66 familial forms. Striatal dopamine transporter was evaluated in two SCA2 and two SCA3/MJD-positive family members, an idiopathic PD patient and a healthy control using carbon (C11) [(11)C]-radiolabeled-CFT positron emission tomography (PET). We found two patients in one familial PD (FPD) family (1.5%) and two sporadic PD patients (0.5%) with expanded CAG repeats in the ATXN2 locus, four patients in two FPD families (3%) and another three sporadic PD patients (0.8%) in the MJD1 locus. [(11)C]-CFT PET in detected members in SCA2 and SCA3/MJD families showed decrements of (11)C-CFT uptake. These findings suggest that a mutation in SCA2 or SCA3/MJD may be one of the genetic causes of PD.