Interaction between compound genetic risk for schizophrenia and high birth weight contributes to social anhedonia and schizophrenia in women.

Schizophrenia is a highly heritable disease, but despite extensive study, its genetic background remains unresolved. The lack of environmental measures in genetic studies may offer some explanation. In recent Finnish studies, high birth weight was found to increase the risk for familial schizophrenia. We examined the interaction between a polygenic risk score for schizophrenia and high birth weight on social anhedonia and schizophrenia in a general population birth cohort. The study sample included 4223 participants from the 1966 Northern Finland Birth Cohort. As a replication sample we used 256 participants from a systematically collected sample of Finnish schizophrenia families. The polygenic risk score comprised of variants published in the large genome-wide meta-analysis for schizophrenia. We found the association between the polygenic risk score and social anhedonia stronger among those with high birth weight, and the same phenomenon was seen for schizophrenia among women, suggesting a gene-environment interaction. Similar results were found within the replication sample. Our results suggest a role for gene-environment interactions in assessing the risk of schizophrenia. Failure to take environmental effects into account may be one of the reasons why identifying significant SNPs for schizophrenia in genome-wide studies has been challenging.