RGK Proteins Preferentially Inhibit Fast-Inactivating Voltage-Gated Calcium Channels: Implications for Human Disease

Abstract

and different types of learning and memory. Recently, large-scale genetic analysis revealed de-novo missense mutations in their pore-forming a 1 -subunit (CACNA1D gene) in 6 patients associated with a neurodevelopmental syndrome including varying degrees of sporadic autism spectrum disorder (ASD, G407R), intellectual disability (A749G), neurological manifestations (including seizures, V401L) and endocrine symptoms (G403D, I750M). A typical hallmark of these mutations are severe gating changes compatible with a gain-of-channel-function. Here we investigated if similar gating changes are observed in a de-novo CACNA1D mutation (IIS4-S5 linker, Ca v 1.3 a 1mut ) which could explain symptoms in a patient diagnosed with a severe developmental disorder of unknown cause. Methods: Mutant (Ca v 1.3 a 1mut ) and wild-type Ca v 1.3 a 1 were co-expressed together with b 3 and a 2 d-1 subunits in tsA-201 cells and calcium currents (15mM) were measured using the whole cell patch-clamp technique. Results: Very similar to the previously characterized mutation V401L (IS6), A749G and I750M (IIS6), Ca v 1.3 a 1mut dramatically shifted the voltagedependence of Ca v 1.3 steady-state activation and inactivation to more negative voltages ($20 mV) without slowing of inactivation. A complete biophysical analysis revealed that these changes are compatible with a mutational gainof-function phenotype. Conclusion: By demonstrating the typical gating changes previously shown by us for CACNA1D de-novo missense mutations we propose that Ca v 1.3 a 1mut also explains the symptoms in this patient with a severe developmental disorder. Patients carrying such mutations may benefit from treatment with already available L-type Ca 2þ -channel blockers, such as nimodipine. Such CACNA1D missense mutations are likely underreported in large-scale genetic analyses. Support: Austrian Science Fund (FWF F4402, W1101).