Shared genetic architecture between psychiatric and insulin-related traits in the general population

Psychiatric conditions, like Attention-Deficit/Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD), and Obsessive-Compulsive Disorder (OCD) are complex heritable disorders that frequently co-occur with insulin resistance (IR)-related conditions, such as obesity and type 2 diabetes mellitus. Traditional genetic case-control comparisons are challenged by the extent of heterogeneity and comorbidity within and across these conditions. In this study we used psychiatry-related traits in the general population in multivariate analyses to explore the potential genetic links with insulin-related traits. Using large-scale genetic studies (N = 17,666-697,734) genomic structural equation modeling was applied to identify the factor structure best representing the joint genetic architecture of traits in the population that are linked to ADHD, ASD, and OCD, and five IR-related measures: body mass index (BMI), fasting plasma glucose (FPG), fasting plasma insulin, glycated haemoglobin (HbA1c), and the Homeostatic Model assessment for IR (HOMA-IR). Next, multivariate genome-wide association analyses were performed on the psychiatry-IR related factors to explore genetic associations, followed by functional mapping and annotation of the genetic results. Factor analyses indicated that a three-factor model fitted the data best (χ2(df = 9) = 18.79, AIC = 56.8, CFI = 0.99, SRMR = 0.068). Two of the three genetic factors included both psychiatric and insulin-related traits, one factor connected ADHD symptoms with three IR-related measures (BMI, FPG, HbA1c) and another factor OCD symptoms with HbA1c. Genetic analyses revealed 57 genes significantly associated with the ADHD-IR factor (p < 2.961e-06) and one gene, MTNR1B (p = 3.44e-07), with the OCD/OCS-IR factor. Neurodevelopmental pathways were associated to the psychiatric and insulin-related factors and expression of the associated variants was enriched in brain tissues and during brain development. These findings suggest a shared genetic liability between psychiatric symptoms and IR-related measures in the general population, indicating that the link between insulin resistance and psychiatry is not solely driven by disorder status and offering new perspectives on the underlying molecular genetics between them.