GDF11 and schizophrenia: Correlation analysis showed significant negative associations of plasma levels of GDF-11 with the PANSS total score (r = −0.475, p < 0.001), the positive symptoms score (r = −0.357, p = 0.002), the negative symptoms score (r = −0.310, p = 0.006), or the general psychopathological score (r = −0.388, p = 0.001) in patients with schizophrenia.