Four major psychiatric disorders in childhood and early adulthood and siblings' subsequent socioeconomic status: a nationwide register study.

Purpose: Previous studies document the clustering of major psychiatric disorders (MPDs) - schizophrenia, bipolar disorder, depression, and anxiety - among siblings. Few studies have, however, examined whether MPDs during childhood and early adulthood are associated with siblings' future socioeconomic status (SES).

Methods: This cohort study included 57,537 full siblings, 4653 paternal, and 5053 maternal half-siblings of individuals with MPDs (affected probands) born in Finland between 1970 and 1990. We defined the reference groups as identical types of siblings of individuals without an MPD diagnosis (unaffected probands) and followed both siblings of the affected and unaffected probands until December 31, 2020. MPDs diagnosed among the affected probands at ages 5-25 was obtained from the Finnish Care Register. Their siblings' SES was measured based on employment status, annual disposable income, and educational achievement. Logistic regression, median regression, and generalized estimating equations (GEE) were used to estimate the associations.

Results: Compared to the siblings of the unaffected probands, the odds of unemployment at the end of follow-up were 35% higher (95% CI: 1.31-1.39) in full siblings of affected probands with an MPD. Full siblings of affected probands were also more likely not to achieve a higher education level (aOR: 1.28, 95% CI 1.24-1.31). The median annual disposable income was 1255.9 EUR lower (95% CI: -1385.6, -1126.3) in full siblings of affected probands. Similar but weaker associations were observed in maternal and paternal half-siblings. Results from GEE models using repeated measurements of income and unemployment were similar.

Conclusion: Our findings suggest that the socioeconomic consequences associated with MPDs extend to siblings.