A Rare Schizophrenia Risk Variant of CACNA1I Disrupts Ca3.3 Channel Activity

CACNA1I is a candidate schizophrenia risk gene. It encodes the pore-forming human Ca3.3 α1 subunit, a subtype of voltage-gated calcium channel that contributes to T-type currents. Recently, two de novo missense variations, T797M and R1346H, of hCa3.3 were identified in individuals with schizophrenia. Here we show that R1346H, but not T797M, is associated with lower hCa3.3 protein levels, reduced glycosylation, and lower membrane surface levels of hCa3.3 when expressed in human cell lines compared to wild-type. Consistent with our biochemical analyses, whole-cell hCa3.3 currents in cells expressing the R1346H variant were ~50% of those in cells expressing WT hCa3.3, and neither R1346H nor T797M altered channel biophysical properties. Employing the NEURON simulation environment, we found that reducing hCa3.3 current densities by 22% or more eliminates rebound bursting in model thalamic reticular nucleus (TRN) neurons. Our analyses suggest that a single copy of Chr22: 39665939G > A CACNA1I has the capacity to disrupt Ca3.3 channel-dependent functions, including rebound bursting in TRN neurons, with potential implications for schizophrenia pathophysiology.