Two heterozygous Cav3.2 channel mutations in a pediatric chronic pain patient: recording condition-dependent biophysical effects

Abstract

We report expression system-dependent effects of heterozygous mutations (P769L and A1059S) in the Cav3.2 CACNA1H gene identified in a pediatric patient with chronic pain and absence seizures. The mutations were introduced individually into recombinant channels and then analyzed by means of electrophysiology. When both mutants were coexpressed in tsA-201 cells, we observed a loss of channel function, with significantly smaller current densities across a wide range of voltages (−40 to +20 mV). In addition, when both mutant channels were co-expressed, the channels opened at a more depolarizing potential with a~5-mV right shift in the half-activation potential, with no changes in half-inactivation potential and the rate of recovery from inactivation. Interestingly, when both mutants were co-expressed in the neuronalderived CAD cells in a different extracellular milieu, the effect was remarkably different. Although not statistically significant (p < 0.07), current densities appeared augmented compared to wild-type channels and the difference in the halfactivation potential was lost. This could be attributed to the replacement of extracellular sodium and potassium with tetraethylammonium chloride. Our results show that experimental conditions can be a confounding factor in the biophysical effects of T-type calcium channel mutations found in certain neurological disorders.

CACNA1H Mutations Are Associated With Different Forms of Primary Aldosteronism

“…CACNA1H variants have been previously associated with epileptic disorders (such as childhood absence epilepsy, febrile seizures, myoclonic–astatic epilepsy, and juvenile absence epilepsy) (Chen et al, 2003, Heron et al, 2007, Khosravani et al, 2004, Khosravani et al, 2005), autism spectrum disorders (Splawski et al, 2006) and chronic pain in pediatric patients (Souza et al, 2016). More recently, a recurrent CACNA1H mutation, p.Met1549Val, has been identified in a cohort of patients with PA and hypertension before age 10 with no history of seizures, neurologic or neuromuscular disorders (Scholl et al, 2015).…”

A rare CACNA1H variant associated with amyotrophic lateral sclerosis causes complete loss of Cav3.2 T-type channel activity

“…Our electrophysiological analysis showed a moderate reduction of the expression of the P1210L channel variant at the cell surface and an associated reduction in the T-type conductance. We cannot entirely rule out the possibility that the phenotypic expression of the P1210L variant could have differed when introduced into a different Ca v 3.2 splice variant [18], or when functionally assessed under different experimental conditions [19], but our experimental data together with the relatively high occurrence of this variant in the general population strongly suggest that it is indeed unlikely to be pathogenic. In contrast, the ΔI153 variant had never been reported and was predicted to be deleterious.…”

CACNA1Hmissense mutations associated with amyotrophic lateral sclerosis alter Cav3.2 T-type calcium channel activity and reticular thalamic neuron firing

“…40 While these variants may not be sufficiently pathogenic to cause the disease on their own, in combination with other variants or environmental factors they could increase disease susceptibility. This may also explain the absence of neurological phenotype in the parents of the individual, who each carry only one of the CACNA1H variants which according to our simulation experiment is not sufficient to significantly alter neuronal excitability.…”