In this ante mortem study, it was found that more increased serum GDNF levels were observed in PSP-P, though this observation was not confirmed in PSP-RS, which suggests that serum GDNF levels may primarily increase as a protective mechanism; this hypothesis aligns with the results of GDNF studies in Parkinson’s disease, where the factor had an inhibitory influence on the deterioration of certain clinical features (discussed above). This evidence concerns the gene GDNF and Parkinson disease.