GDF15 and supranuclear palsy, progressive, 1: In patients with PSP, serum GDF-15 levels showed a significant positive correlation with age (r = 0.565; p = 0.028) but not with disease duration (r = −0.319; p = 0.247) or mRS score (r = 0.130; p = 0.643; Figure 3A–C).