Psychiatric disorders are highly prevalent and notable contributors to the global burden of disease, directly accounting for more than a quarter of all non-fatal burden, worldwide.¹ The severity of their global health effect generated the need to identify the etiological factors that induce the development of schizophrenia, bipolar disorder, and other psychosis-spectrum diagnoses. Despite the attention given in this field, the nature of the aetiology and development of such disorders is highly complex and multideterminant.²
It has been well-established that mental health is affected by dynamic and bidirectional interactions of organismic and environmental variations, as well as socioeconomic contexts and social behaviors.³ As part of this theory, several models have been developed, such as the diathesis-stress model,⁴ the biological-sensitivity-to-context-theory model⁵ and the differential susceptibility theory model.⁵ To date, however, the former frameworks have been barely used for studies that have examined a truly lifespan perspective or the development of psychosis-spectrum disorders from an early age.

Hastings et al. approached these issues to explore the impact of socioeconomic contexts and problematic social behaviours in childhood on the development of psychotic disorders in adulthood.⁶ Scientific literature has indicated that family poverty, aggressive behaviour and social withdrawal are characteristics of children who later developed schizophrenia.^7,8 However, this research field still draws a lot of attention, in order to achieve early identification of and further the development of preventive interventions for psychotic disorders.⁶
 

Hastings et al. conducted a 30-year prospective longitudinal study to better understand the predictors of psychotic-spectrum illnesses by focusing on the additive and interactive contributions of already known risk factors for mental disorders, such as familial conditions, neighbourhood context and poor social functioning.⁹ More specifically, the group studied 3,905 children and their parents, based in the lower income urban contexts of Montreal, over a generational period of marked socioecological changes over maturation, in order to determine the specificity of predictive associations between these changes and the development of psychotic disorders.⁶ Participants’ educational and financial levels were below Quebec and Canadian averages.⁶

His team formed 4 hypotheses:

The results showed that the prevalence of all psychosis diagnoses not attributable to physical ailments by mid-adulthood was higher than expected in 6.25% of participants ⁹, and might be attributable to the target recruitment of an urban, predominantly lower income sample.¹⁰ Being raised in poor neighbourhoods during childhood increased the probability of being consistently diagnosed with a psychotic disorder over the next 30 years, regardless of future socioecological conditions.⁶ Their findings that neighbourhood disadvantage is strongly predictive of mental illnesses for children with social withdrawal symptoms were in line with the literature. ^5,11
 
The conclusion that children raised in most socioeconomically disadvantaged neighbourhoods were at the greatest risk of being diagnosed with schizophrenia or bipolar disorder with psychosis when they would become adults supported the theoretical models. These models stated that socioeconomic deprivation in childhood has a key role in the later development of psychotic diagnoses, due to several life stressors such as environmental toxins, more crime incidents and high parental distress.^12,13
 

Hastings et al. have also investigated if the gender was predictive of the future diagnosis of schizophrenia and bipolar disorders and found out that among less socially withdrawn boys, greater aggression predicted more schizophrenia diagnoses, while socially withdrawn girls predicted fewer diagnoses of bipolar disorder.⁶ The results for males were in line with previous reports, ^14,15 and further extended to the theory that boys, who were about to develop schizophrenia, were more disagreeable and aggressive than their peers.⁶  Their novel observation that schizophrenia in males was specifically predicated on the combination of high aggression and low withdrawal could be the result of poor neurocognitive regulation manifesting as disinhibition, which has been previously posited as a core developmental deficit of schizophrenia.¹⁶ However, Hastings and his team have not found any correlation between highly aggressive females and the development of schizophrenia that has been stated in the past. ^14,15 This might be because social withdrawal in childhood is not a specific predictor of schizophrenia or other psychotic disorders in adulthood, which has been stated in other studies.^9,10
 
A novel finding on their study was that socially withdrawn girls were less likely to develop bipolar disorder later in their life.⁶ This was explained by the fact that girls living in disadvantaged neighbourhoods normally avoid the urban contexts and minimise interactions with risky and delinquent peers, unlike boys in their age.¹⁷ In addition, more withdrawn girls may have been less exposed to environmental risks of their neighbourhoods, while keeping their timidity accepted by their family and peers.¹⁸
 
Limitations of their study involve the use of a single-source measure of psychiatric symptoms, which limits the generalizability of the findings and the largely lower income population that spans two generations.⁶ Heterogeneity due to symptom overlam, comorbidities and different applications of diagnostic criteria across healthcare professionals could also limit the validity of the results. They have reported that diagnostic heterogeneity might have limited the detection of more specific associations with early social behaviours and psychosis-spectrum disorders’ diagnoses and the onset of such disorders.⁶
 

Overall, they have concluded that being raised in socioeconomically disadvantaged neighbourhoods was a significant risk factor for the emergence of psychotic-spectrum disorders later in life, particularly for aggressive and socially withdrawn children. Aggressive males were more likely to develop schizophrenia, without necessarily being withdrawn from their peers, while such characteristics may elicit rejection and isolating responses from social partners that would further increase the risk. Finally, the researchers suggested that economic and social policy interventions addressing the needs of such families and cognitive-behavioural therapies to antisocial children, may prevent the future emergence of schizophrenia and other psychotic illnesses.