Since patients with PD who have comorbid DM tended to have higher serum GDF-15 levels in this study, and patients with DM had higher blood GDF-15 levels than the healthy participants [18], the difference in serum GDF-15 levels distinguished by sex in patients with PSP may have been influenced by the differences in the rate of comorbid DM. The gene discussed is GDF15; the disease is supranuclear palsy, progressive, 1.