Directional anchor genes refine polygenic informed treatment selection in schizophrenia and bipolar disorder

Genetically informed drug development and repurposing is an attractive prospect for improving outcomes in patients with psychiatric illness; however, the effectiveness of these endeavours can be confounded by heterogeneity. In this study, we propose a novel approach that links interventions implicated by disorder-associated genetic risk, at the population level, to a framework that can target these compounds to individuals. Specifically, results from genome-wide association studies are integrated with expression data to prioritise individual "directional anchor" genes for which the predicted risk-increasing direction of expression could be counteracted by an existing drug. While these compounds represent plausible therapeutic candidates, they are not likely to be equally efficacious for all individuals. To account for this heterogeneity, we constructed polygenic scores restricted to variants annotated to the network of genes that interact with each directional anchor gene. These metrics, we call pharmagenic enrichment scores (PES), identify individuals with a higher burden of genetic risk, localised in biological processes related to the candidate drug target, to inform precision drug repurposing. We used this approach to investigate schizophrenia and bipolar disorder and reveal several compounds targeting specific directional anchor genes that could be plausibly repurposed, including antioxidants, vitamins, antiarrhythmics, and lipid modifying agents. These genetic risk scores, mapped to the networks associated with target genes, revealed biological insights that cannot be observed in undifferentiated genome-wide polygenic risk score (PRS). For example, an enrichment of these partitioned scores in schizophrenia cases with otherwise low PRS and distinct correlations with measured biochemical traits. In summary, genetic risk could be used more specifically to direct drug repurposing candidates that target particular genes implicated in psychiatric and other complex disorders.