Risk of schizophrenia in relation to parental origin and genome-wide divergence

Area of Science:

• Psychiatry and Genetics
• Epidemiology

Background:

• Second-generation immigrants exhibit a higher risk of schizophrenia, a phenomenon requiring further explanation.
• Traditional definitions using parental country of birth may be insufficient due to global migration patterns.
• The study investigates alternative measures of ethnicity for second-generation immigrants.

Purpose of the Study:

• To compare the efficacy of parental foreign country of birth versus genetic divergence in identifying second-generation immigrants with increased schizophrenia risk.
• To determine which measure of parental foreign ethnicity best explains the observed schizophrenia risk in Denmark.

Main Methods:

• A case-control study in Denmark included 892 schizophrenia cases and 883 controls born since 1981.
• Genetic divergence was assessed using genome-wide genotypic data and principal component analyses.
• Parental foreign country of birth was obtained from the Danish Civil Registration System.

Main Results:

• Individuals with foreign-born parents had a 1.94 times increased risk of schizophrenia (RR 1.94, 95% CI 1.41-2.65).
• Genetically divergent individuals showed a 2.43 times increased risk (RR 2.43, 95% CI 1.55-3.82).
• Mutual adjustment revealed no significant difference between the two measures' impact on schizophrenia risk.

Conclusions:

• Genetic divergence and parental foreign country of birth are interchangeable in assessing schizophrenia risk.
• Both measures are valid for identifying second-generation immigrants.
• These findings offer a clearer understanding of schizophrenia risk factors in immigrant populations.