FDG-PET can help distinguish PSP from other parkinsonian syndromes (e.g., Parkinson’s disease and multiple system atrophy) and aid in earlier diagnosis in some cases with inconclusive or normal MRI findings; however, it lacks standardized quantitation methods [20] and yields inconclusive findings in approximately one-third of cases [102], necessitating the use of an additional PET scan with tau-specific PET tracers. This evidence concerns the gene MAPT and Parkinson disease.