Human assembloids reveal the consequences of CACNA1G gene variants in the thalamocortical pathway

Abnormalities in thalamocortical crosstalk can lead to neuropsychiatric disorders. Variants in CACNA1G, which encodes the α1G subunit of the thalamus-enriched T-type calcium channel, are associated with absence seizures, intellectual disability, and schizophrenia, but the cellular and circuit consequences of these genetic variants in humans remain unknown. Here, we developed a human assembloid model of the thalamocortical pathway to dissect the contribution of genetic variants in T-type calcium channels. We discovered that the M1531V CACNA1G variant associated with seizures led to changes in T-type currents in thalamic neurons, as well as correlated hyperactivity of thalamic and cortical neurons in assembloids. By contrast, CACNA1G loss, which has been associated with risk of schizophrenia, resulted in abnormal thalamocortical connectivity that was related to both increased spontaneous thalamic activity and aberrant axonal projections. These results illustrate the utility of multi-cellular systems for interrogating human genetic disease risk variants at both cellular and circuit level. •Generation of hiPS cell-derived diencephalic organoids containing thalamic neurons•Integration of cortical and diencephalic organoids to form thalamocortical assembloids•M1531V CACNA1G variant alters T-type currents, leading to hyperactivity in assembloids•Loss of CACNA1G changes thalamocortical connectivity and increases thalamic activity Kim et al. developed a human assembloid to investigate the effects of calcium channel function on the thalamocortical pathway. The M1531V CACNA1G variant altered T-type currents and induced hyperactivity, while CACNA1G loss changed connectivity and thalamic activity. This highlights the utility of assembloids in identifying circuit-level disease phenotypes.