GDNF and supranuclear palsy, progressive, 1: The significantly increased levels of GDNF in the serum of patients with PSP-P and less increased in PSP-RS may suggest that in PSP, the levels of GDNF in the serum may initially rise significantly as a protective mechanism, which may partly come up with results of studies on GDNF in PD, where the factor inhibited the deterioration of certain clinical features.