GDF15 and multiple system atrophy: The serum GDF-15 level in patients with PD (1394.67 ± 558.46 pg/mL) did not differ significantly from that in patients with PSP (1491.27 ± 620.78 pg/mL; p = 0.573) but was significantly higher than that in patients with MSA (978.42 ± 334.66 pg/mL; p = 0.017).