GDF15 and neurodegenerative disease: The pooled results of the random effect model indicated GDF15 levels were significantly higher in patients with neurodegenerative disease than healthy people (SMD = 0.92, 95% CI: 0.44–1.40, Z = 3.75, p < 0.001), with high heterogeneity among studies (I2 = 86.1%, p < 0.001).