Convergent and Divergent Cerebellar Alterations in 22q11.2 Copy Number Variants
BackgroundIndividuals with copy number variants (CNVs) at 22q11.2 are at elevated risk for neurodevelopmental and psychiatric disorders, including autism spectrum disorder and intellectual disability. For psychosis, effects diverge, with 22q11.2 deletion (22qDel) conferring one of the highest known risks for schizophrenia, while duplication (22qDup) may be protective. Prior investigations of neurobiological mechanisms in 22q11.2 CNVs have predominantly focused on the cerebrum, whereas the cerebellum--a region increasingly recognized for its contributions to cognitive, affective, and social processes--remains underexplored and represents a promising target for investigation. Although alterations in cerebellar structure have been reported in 22qDel, they remain largely unexplored in 22qDup. This study provides the first characterization of regional cerebellar volumes in 22qDup and the first direct comparison of cerebellar structure across 22q11.2 CNVs, offering a unique opportunity to identify shared and distinct neurobiological mechanisms with implications for understanding cerebellar contributions to brain-behavior relationships in CNV carriers. MethodsWe analyzed 514 longitudinally collected structural Magnetic Resonance Imaging (MRI) scans of 111 individuals with 22qDel, 37 individuals with 22qDup, and 167 typically developing (TD) controls. Total and regional cerebellar volumes were quantified using ACAPULCO, a deep-learning-based parcellation method that segments the cerebellum into 28 subregions. Group differences in cerebellar volumes, as well as their associations with cognition, autism-related traits, and psychosis-risk symptoms, were examined using linear mixed-effects models. False discovery rate (FDR) correction was applied to control for multiple comparisons where appropriate. ResultsIn relation to TD controls, cerebellar volumes were broadly reduced in 22qDel, whereas cerebellar alterations in 22qDup were more modest and variable. Regional analyses revealed both linear (22qDel < TD < 22qDup) and nonlinear (22qDel {approx} 22qDup < TD; 22qDel < 22qDup < TD) gene-dosage patterns, though not all reached significance. Vermis VII was significantly reduced in both CNVs but showed no relationship to behavioral differences. In contrast, reduction of Right Lobule VIIIA was associated with greater social impairment in 22qDup. Unlike TD controls, this region was not associated with IQ in 22qDup, suggesting CNV-specific alterations in cerebellar-behavior relationships. ConclusionThese findings indicate that reciprocal CNVs at the 22q11.2 locus both affect cerebellar structure, yet their functional consequences diverge, suggesting overlapping but distinct pathways to clinical risk. They underscore the cerebellums multifaceted role in neurodevelopment and highlight the need for studies examining broader cognitive and socio-affective domains, as well as cerebellar-cortical connectivity, to clarify links to clinical outcomes.