Various psychological and biological pathways have been proposed as mediators between childhood adversity (CA) and psychosis. A systematic review of the evidence in this domain is needed. Our aim is to systematically review the evidence on psychological and biological mediators between CA and psychosis across the psychosis spectrum. This review followed PRISMA guidelines. Articles published between 1979 and July 2019 were identified through a literature search in OVID (PsychINFO, Medline and Embase) and Cochrane Libraries. The evidence by each analysis and each study is presented by group of mediator categories found. The percentage of total effect mediated was calculated. Forty-eight studies were included, 21 in clinical samples and 27 in the general population (GP) with a total of 82 352 subjects from GP and 3189 from clinical studies. The quality of studies was judged as ‘fair’. Our results showed (i) solid evidence of mediation between CA and psychosis by negative cognitive schemas about the self, the world and others (NS); by dissociation and other post-traumatic stress disorder symptoms; and through an affective pathway in GP but not in subjects with disorder; (iii) lack of studies exploring biological mediators. We found evidence suggesting that various overlapping and not competing pathways involving post-traumatic and mood symptoms, as well as negative cognitions contribute partially to the link between CA and psychosis. Experiences of CA, along with relevant mediators should be routinely assessed in patients with psychosis. Evidence testing efficacy of interventions targeting such mediators through cognitive behavioural approaches and/or pharmacological means is needed in future.

Pathophysiological mechanisms of major depressive disorder (MDD) seem to be associated with oxidative stress pathways and altered purinergic metabolism. We conducted a systematic review and meta-analysis to estimate if subjects with MDD might have reduced levels of antioxidant uric acid, considering also potential influence of antidepressant treatment. We searched the main Electronic Databases, identifying 14 studies that met our inclusion criteria. Meta-analyses were carried out generating pooled Hedges' g and mean differences (MDs), using random-effects models. Heterogeneity across studies and risk of publication bias were estimated using standard methods. Relevant sensitivity and meta-regression analyses were conducted. Subjects with MDD had levels of uric acid lower than healthy controls (Hedges' g = -0.30; p = 0.003). Overall between-study heterogeneity was high (I = 76.3%). The effect was significant among studies including drug naïve/free MDD individuals (Hedges' g = -0.55; p = 0.023), but not among those involving treated subjects (Hedges' g = -0.15; p = 0.062). Relevant quality- and heterogeneity-based sensitivity analyses, as well as meta-regressions, confirmed these findings. In addition, uric acid levels significantly, though inconsistently (I = 79.2%), increased after treatment (MD = +0.71 mg/dL; p < 0.001), regardless of follow-up duration (p = 0.518). Our meta-analysis shows that subjects with MDD have lower levels of uric acid. Since antidepressant treatment seems to influence this association, our findings support the hypothesis that uric acid levels may represent a state marker of MDD. Nevertheless, the potential role of additional factors that might clarify the nature of this association deserves further research.

Despite the accepted link between childhood abuse and positive psychotic symptoms, findings between other adversities, such as neglect, and the remaining dimensions in people with psychosis have been inconsistent, with evidence not yet reviewed quantitatively. The aim of this study was to systematically examine quantitatively the association between broadly defined childhood adversity (CA), abuse (sexual/physical/emotional), and neglect (physical/emotional) subtypes, with positive, negative, depressive, manic, and disorganized dimensions in those with psychosis. A search was conducted across EMBASE, MEDLINE, PsychINFO, and Cochrane Libraries using search terms related to psychosis population, CA, and psychopathological dimensions. After reviewing for relevance, data were extracted, synthesized, and meta-analyzed. Forty-seven papers were identified, including 7379 cases across 40 studies examining positive, 37 negative, 20 depressive, 9 disorganized, and 13 manic dimensions. After adjustment for publication bias, general adversity was positively associated with all dimensions (ranging from r = 0.08 to r = 0.24). Most forms of abuse were associated with depressive (ranging from r = 0.16 to r = 0.32), positive (ranging from r = 0.14 to r = 0.16), manic (r = 0.13), and negative dimensions (ranging from r = 0.05 to r = 0.09), while neglect was only associated with negative (r = 0.13) and depressive dimensions (ranging from r = 0.16 to r = 0.20). When heterogeneity was found, it tended to be explained by one specific study. The depressive dimension was influenced by percentage of women (ranging from r = 0.83 to r = 1.36) and poor-quality scores (ranging from r = −0.21 and r = −0.059). Quality was judged as fair overall. Broadly defined adversity and forms of abuse increase transdimensional severity. Being exposed to neglect during childhood seems to be exclusively related to negative and depressive dimensions suggesting specific effects.

The GAP multidisciplinary study carried out in South London, recruited 410 first episode of psychosis patients and 370 controls; the aim was to elucidate the multiple genetic and environmental factors influencing the onset and outcome of psychosis.The study demonstrated the risk increasing effect of adversity in childhood (especially parental loss, abuse, and bullying) on onset of psychosis especially positive symptoms.Adverse life events more proximal to onset, being from an ethnic minority, and cannabis use also played important roles; indeed, one quarter of new cases of psychosis could be attributed to use of high potency cannabis. The "jumping to conclusions" bias appeared to mediate the effect of lower IQ on vulnerability to psychosis.We confirmed that environmental factors operate on the background of polygenic risk, and that genetic and environment act together to push individuals over the threshold for manifesting the clinical disorder. The study demonstrated how biological pathways involved in the stress response (HPA axis and immune system) provide important mechanisms linking social risk factors to the development of psychotic symptoms. Further evidence implicating an immune/inflammatory component to psychosis came from our finding of complement dysregulation in FEP. Patients also showed an upregulation of the antimicrobial alpha-defensins, as well as differences in expression patterns of genes involved in NF-κB signaling and Cytokine Production.Being of African origin not only increased risk of onset but also of a more difficult course of illness. The malign effect of childhood adversity predicted a poorer outcome as did continued use of high potency cannabis.

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