Lobular and Voxel‐Wise Genetic Influences on Cerebellar Gray Matter Volume and Associations With Social and Trait Anxiety in Twins

The cerebellum supports motor, cognitive, and affective functions, but the spatial pattern of genetic influence on its morphology and its relevance to anxiety traits remains unclear. Using structural MRI data from monozygotic and dizygotic twins (298 participants), we estimated additive genetic and environmental contributions to cerebellar gray matter volume at lobular and voxel scales. Monozygotic twins showed higher intra‐pair correlations than dizygotic twins across cerebellar regions, indicating genetic influence with marked spatial heterogeneity: effects were strongest in posterior and vermal lobules (notably lobule IX, Crus I/II, and vermis VII–VIII) and more moderate in anterior motor‐related lobules; cerebellar white matter also showed strong genetic influence. Voxel‐wise mapping confirmed this pattern and revealed within‐lobule heterogeneity not captured by lobular averaging, with additive genetic factors explaining ~45% of voxel‐level variance and minimal shared environmental effects. Social (measured via the Liebowitz Social Anxiety Scale‐Self Report; LSAS‐SR) and trait (State–Trait Anxiety Inventory; STAI‐T) anxiety were substantially heritable, whereas phenotypic, genetic, and unique environmental correlations with cerebellar volumes were small and did not survive multiple‐comparisons correction. These results show that genetic influence on cerebellar structure is strongly spatially heterogeneous and scale‐dependent, whereas associations between cerebellar gray matter volume and anxiety severity are weak in this non‐clinical adult sample.