Investigation of CACNA1I Cav3.3 Dysfunction in Hemiplegic Migraine

Abstract

Familial hemiplegic migraine (FHM) is a severe neurogenetic disorder for which three causal genes, CACNA1A, SCN1A, and ATP1A2, have been implicated. However, more than 80% of referred diagnostic cases of hemiplegic migraine (HM) are negative for exonic mutations in these known FHM genes, suggesting the involvement of other genes. Using whole-exome sequencing data from 187 mutation-negative HM cases, we identified rare variants in the CACNA1I gene encoding the T-type calcium channel Cav3.3. Burden testing of CACNA1I variants showed a statistically significant increase in allelic burden in the HM case group compared to gnomAD (OR = 2.30, P = 0.00005) and the UK Biobank (OR = 2.32, P = 0.0004) databases. Dysfunction in T-type calcium channels, including Cav3.3, has been implicated in a range of neurological conditions, suggesting a potential role in HM. Using patch-clamp electrophysiology, we compared the biophysical properties of five Cav3.3 variants (p.R111G, p.M128L, p.D302G, p.R307H, and p.Q1158H) to wild-type (WT) channels expressed in HEK293T cells. We observed numerous functional alterations across the channels with Cav3.3-Q1158H showing the greatest differences compared to WT channels, including reduced current density, right-shifted voltage dependence of activation and inactivation, and slower current kinetics. Interestingly, we also found significant differences in the conductance properties exhibited by the Cav3.3-R307H and -Q1158H variants compared to WT channels under conditions of acidosis and alkalosis. In light of these data, we suggest that rare variants in CACNA1I may contribute to HM etiology.

Electrophysiological characterization of a Cav3.2 calcium channel missense variant associated with epilepsy and hearing loss

“…Given that the R132H variant implicates the introduction of histidine within the extracellular end of the second transmembrane helix of Ca v 3.2, we assessed the effects of extracellular pH changes, alkalization (pH e 8.0) and acidification (pH e 6.5), on T-type currents. Consistent with previous results on T-type channels [11,12], extracellular alkalization and acidification produced a significant increase and decrease of the T-type current, respectively, in both Ca v 3.2 WT-and R132H-expressing cells (Fig. 1i, top panels).…”

Unravelling the Genetic Landscape of Hemiplegic Migraine: Exploring Innovative Strategies and Emerging Approaches

“…Furthermore, CACNA1I and CACNA1H may be implicated in HM [39,125]. Patients with HM have been found to have an increased burden of missense variants in these two genes, further supporting the hypothesis that the genetic architecture of HM extends beyond the currently known genetic area for HM.…”

“…Adding to the complexity of understanding the interplay between the human genome and migraine development is the fact that the involvement of mutations in the three known FHM genes is not always established in patients with FHM; this supports the speculation that there might be unknown genes involved in FHM [38]. For example, a recent study found that genetic variants in the CACNA1I gene might contribute to the aetiology of HM [39]. A Danish study on FHM revealed that only 14% of the affected individuals had mutations in the three known genes.…”

“…In comparison, a large study conducted in Finland reported mutations in only 9% of 45 families with FHM [5,40]. Studies concluded that the three known FHM genes account for only 7-14% of FHM cases, supporting the notion that other loci might be responsible for developing this debilitating condition [5,39,41,42].…”