Brain-derived neurotrophic factor (BDNF) is a key modulator of neuroplasticity and has an important role in determining the susceptibility to severe psychiatric disorder with a significant neurodevelopmental component such as major psychoses. Indeed, a potential association between BDNF serum levels and schizophrenia (SCZ) and schizoaffective disorder (SAD) has been tested in diverse studies and a considerable amount of them found reduced BDNF levels in these disorders. Here, we aimed at testing the association of BDNF serum levels with several demographic, clinical, and psychometric measures in 105 patients with SCZ and SAD, assessing the moderating effect of genetic variants within the BDNF gene. We also verified whether peripheral BDNF levels differed between patients with SCZ and SAD. Our findings revealed that BDNF serum levels are significantly lower in patients affected by SCZ and SAD presenting more severe depressive symptomatology. This finding awaits replication in future independent studies and points to BDNF as a possible prognostic indicator in major psychoses.

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The persistence of depressive morbidity is frequent in bipolar disorder, and the pharmacological management of this symptomatology often lacks effectiveness. This systematic review aimed to summarize the results of the naturalistic observational studies on the pharmacological treatment of bipolar depression published through April 2022. The certainty of evidence was evaluated according to the GRADE approach. In sum, 16 studies on anticonvulsants, 20 on atypical antipsychotics, 2 on lithium, 28 on antidepressants, and 9 on other compounds were found. Lamotrigine, quetiapine, aripiprazole, and ketamine were the most investigated compounds. Overall, the results support the recommendations regarding the effectiveness of lamotrigine and quetiapine. In contrast to the current recommendations, aripiprazole was shown to be effective and generally well tolerated. Additionally, SSRIs were shown to be effective, but, since they were associated with a possibly higher switch risk, they should be used as an adjunctive therapy to mood stabilizers. Lithium was only studied in two trials but was shown to be effective, although the serum concentrations levels were not associated with clinical response. Finally, ketamine showed divergent response rates with a low certainty of evidence and, so far, unclear long-term effects. Heterogeneity in diagnosis, sample sizes, study designs, reporting of bias, and side effects limited the possibility of a head-to-head comparison.