Socioeconomic status and severe mental disorders: a bidirectional multivariable Mendelian randomisation study

Area of Science:

• Psychiatry
• Genetics
• Epidemiology

Background:

• Socioeconomic status (SES) is linked to severe mental disorders (SMD), but the causal direction between income/education and mental illness remains unclear.
• Understanding these relationships is crucial for public health interventions.

Purpose of the Study:

• To investigate bidirectional causal relationships between genetic liability for income and educational attainment (EA) and three SMDs: schizophrenia, bipolar disorder (BD), and depression.
• To differentiate the roles of income and EA in the etiology of SMDs.

Main Methods:

• Utilized a bidirectional, two-sample Mendelian randomization (MR) study design.
• Employed univariable (UVMR) and multivariable (MVMR) MR analyses using large genome-wide association study summary statistics for SES phenotypes and SMDs.

Main Results:

• Genetic liability to higher income was associated with a reduced risk of schizophrenia and depression, with a smaller reverse effect observed.
• Genetic liability to EA showed bidirectional negative associations with depression and positive associations with BD.
• MVMR revealed that after accounting for income, EA had a bidirectional positive association with BD and schizophrenia.

Conclusions:

• SES and SMD have heterogeneous causal links, with distinct pathways for income and EA.
• Income demonstrates a negative bidirectional association with schizophrenia and depression risk.
• EA shows a positive bidirectional relationship with BD and schizophrenia, particularly when income is considered.