Tiered modelling of a <i>CACNA1A</i> D1634N mutation linked to ataxia, epilepsy and cognitive deficits

Missense mutations in CACNA1A, which encodes CaV2.1 voltage-gated calcium channels, underlie serious neurological diseases with inadequate treatment options. Developing new therapies for CACNA1A diseases is hindered by: 1) unknown biophysical impact of many mutations, 2) limited knowledge of genotype effects on channel function and behavioural phenotype, and 3) dearth of animal models mimicking the human disease. Here, we focus on a CACNA1A missense mutation (D1634N) identified in a patient with ataxia, epilepsy, moderate intellectual disability, and mild cerebellar loss. Heterologously expressed D1634N channels displayed a significantly decreased whole-cell current amplitude, a +25-mV shift in activation V1/2, and diminished single-channel open probability, indicating a loss-of-function (LoF). Patient-specific cortical neurons derived from induced pluripotent stem cells displayed enhanced intrinsic excitability compared to isogenic controls. Heterozygous knock-in mice with the analogous mutation (D1585N) displayed ataxia, absence epilepsy, and cognitive deficits, mirroring the human behavioural phenotype. Purkinje cell and cerebellar slice electrophysiology revealed a reduced whole-cell CaV2.1 current with a right-shifted V1/2 of activation, altered Purkinje cell excitability, and changes in presynaptic vesicle release probability at the parallel fibre to Purkinje neuron input. The results introduce a new CACNA1A LoF mutation and highlight the power of combined heterologous expression, iPSC neurons, and animal model studies to provide complementary insights into the molecular basis of disease with implications for developing therapies.