Being Born in Urban Area May Increase Schizophrenia Risk in Adolescence

In the United Kingdom, researchers found data that showed adolescents in an urban environment with high polygenic risk scores had a higher risk for schizophrenia due to what they hypothesized is caused by threat responses sensitized in the neurobiological pathway from environmental stimuli.

Neighborhood density and social fragmentation at birth are linked to an elevated risk for schizophrenia and other psychotic experiences in adolescence, according to research published in Schizophrenia Bulletin.

Researchers examined the relationship between an urban birth, which are people who were born in a densely populated urban area and both negative and positive psychotic symptoms at 16 and 18 years of age. Data were pulled from the Avon Longitudinal Study of Parents and Children, focusing on pregnant women due between April 1991 and December 1992.

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The total study sample included 11,879 children with available data. Of these participants, 36.1% and 33.4% had data relating to negative symptoms at 16 years and psychotic experiences at 18 years. These children were less deprived and socially fragmented when compared with the rest of England but had “similar levels of inequality and were more densely populated.”

Distribution of schizophrenia polygenic risk scores did not differ by neighborhood population density or inequality at birth; however, children who were born in more deprived neighborhoods (first vs third tertile relative risk ratio [RRR] 1.07; 95% CI, 1.01-1.14) and socially fragmented areas had higher polygenic risk scores for schizophrenia (second tertile RRR 1.07; 95% CI, 1.01-1.14 and third tertile RRR 1.12; 95% CI, 1.06-1.19).

With greater neighborhood deprivation, higher population density, and social fragmentation at birth, prevalence of psychotic experiences in adolescence increased. Researchers noted a crude association between population density at birth and the odds of reporting psychotic experiences in adolescence, which remained after full multivariable adjustment (odds ratio [OR] 1.57; 95% CI, 1.14-2.17).

The relationship between greater neighborhood social fragmentation and more prevalent negative symptoms in adolescence persisted in both crude and multivariable models; children born in the most fragmented neighborhoods had the greatest risk (OR 1.43; 95% CI, 1.06-1.95).

Limitations of the study include the cohort attrition between birth and late adolescence. The researchers noted that children with higher polygenic risk scores for schizophrenia are “more likely to be lost to follow-up,” possibly resulting in underestimates of polygenic risk score effects.

“Birth into more densely populated and socially fragmented environments increased risk for positive and negative psychotic phenomena in adolescence, respectively,” the researchers of the study concluded, “suggesting that different forms of neighborhood social adversity may impinge on different psychopathologies associated with the clinical expression of psychosis.”

Solmi F, Lewis G, Zammit S, Kirkbride JB. Neighborhood characteristics at birth and positive and negative psychotic symptoms in adolescence: Findings from the ALSPAC Birth Cohort [published online June 5, 2019]. Schizophr Bull. doi: 10.1093/schbul/sbz049