Human assembloids reveal the consequences ofCACNA1Ggene variants in the thalamocortical pathway

Abnormalities in crosstalk between the thalamus and the cerebral cortex are thought to lead to severe neuropsychiatric disorders, such as epilepsy and psychotic disorders. Pathogenic variants in theCACNA1Ggene, which encodes the α1G subunit of the thalamus-enriched T-type voltage-gated calcium channel CaV3.1, are associated with absence seizures, intellectual disability, and schizophrenia, but the cellular and circuit level consequences of these genetic variants in humans remain unknown. Here, we developed anin vitrohuman assembloid model of the thalamocortical pathway to systematically dissect the contribution of genetic variants in T-type calcium channels. We discovered that aCACNA1Gvariant (M1531V) associated with seizures led to hypersynchronous activity in the thalamus and in cortical neurons in thalamo-cortical assembloids. In contrast,CACNA1Gloss, which has been associated with risk of schizophrenia, resulted in abnormal thalamocortical connectivity that was related to both increased spontaneous thalamic activity and aberrant thalamic axonal projections. Taken together, these results illustrate the utility of organoid and assembloid systems for interrogating human genetic disease risk variants at both cellular and circuit level.