The characterization of new de novo CACNA1G variants affecting the intracellular gate of Cav3.1 channel broadens the spectrum of neurodevelopmental phenotypes in SCA42ND.

Purpose: Missense de novo variants in CACNA1G, which encodes the Cav3.1 T-type calcium channel, have been associated with a severe, early-onset form of cerebellar disorder with neurodevelopmental deficits (SCA42ND). We explored a large series of pediatric cases carrying heterozygous variants in CACNA1G to further characterize genotype-phenotype correlations in SCA42ND.

Methods: We describe 19 patients with congenital CACNA1G-variants including 6 new heterozygotes of the recurrent SCA42ND variants, p.(Ala961Thr) and p.(Met1531Val), and 8 unreported variants including 7 missense variants, mainly de novo. We carried out genetic and structural analyses of all variants. Patch-clamp recordings were performed to measure their channel activity.

Results: We provide a consolidated clinical description for the patients carrying p.(Ala961Thr) and p.(Met1531Val). The new variants associated with the more severe phenotypes are found in the Cav3.1 channel intracellular gate. Calcium currents of these Cav3.1 variants showed slow inactivation and deactivation kinetics, and increase in window current, supporting a gain of channel activity. On the contrary, the p.(Met197Arg) variant (IS4-S5 loop) resulted in a loss of channel activity.

Conclusion: This detailed description of several de novo missense pathogenic variants in CACNA1G, including 13 previously reported cases, supports a clinical spectrum of congenital CACNA1G syndrome beyond spinocerebellar ataxia.