Browsing by Author "Jurkovicova-Tarabova, Bohumila"

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    A rare CACNA1H variant associated with amyotrophic lateral sclerosis causes complete loss of Cav3.2 T-type channel activity
    (2020-03-06) Stringer, Robin N; Jurkovicova-Tarabova, Bohumila; Huang, Sun; Haji-Ghassemi, Omid; Idoux, Romane; Liashenko, Anna; Souza, Ivana A; Rzhepetskyy, Yuriy; Lacinova, Lubica; Van Petegem, Filip; Zamponi, Gerald W; Pamphlett, Roger; Weiss, Norbert
    Abstract Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the progressive loss of cortical, brain stem and spinal motor neurons that leads to muscle weakness and death. A previous study implicated CACNA1H encoding for Cav3.2 calcium channels as a susceptibility gene in ALS. In the present study, two heterozygous CACNA1H variants were identified by whole genome sequencing in a small cohort of ALS patients. These variants were functionally characterized using patch clamp electrophysiology, biochemistry assays, and molecular modeling. A previously unreported c.454GTAC > G variant produced an inframe deletion of a highly conserved isoleucine residue in Cav3.2 (p.ΔI153) and caused a complete loss-of-function of the channel, with an additional dominant-negative effect on the wild-type channel when expressed in trans. In contrast, the c.3629C > T variant caused a missense substitution of a proline with a leucine (p.P1210L) and produced a comparatively mild alteration of Cav3.2 channel activity. The newly identified ΔI153 variant is the first to be reported to cause a complete loss of Cav3.2 channel function. These findings add to the notion that loss-of-function of Cav3.2 channels associated with rare CACNA1H variants may be risk factors in the complex etiology of ALS.
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    De novo SCN8A and inherited rare CACNA1H variants associated with severe developmental and epileptic encephalopathy
    (2021-08-16) Stringer, Robin N.; Jurkovicova-Tarabova, Bohumila; Souza, Ivana A.; Ibrahim, Judy; Vacik, Tomas; Fathalla, Waseem M.; Hertecant, Jozef; Zamponi, Gerald W.; Lacinova, Lubica; Weiss, Norbert
    Abstract Developmental and epileptic encephalopathies (DEEs) are a group of severe epilepsies that are characterized by seizures and developmental delay. DEEs are primarily attributed to genetic causes and an increasing number of cases have been correlated with variants in ion channel genes. In this study, we report a child with an early severe DEE. Whole exome sequencing showed a de novo heterozygous variant (c.4873–4881 duplication) in the SCN8A gene and an inherited heterozygous variant (c.952G > A) in the CACNA1H gene encoding for Nav1.6 voltage-gated sodium and Cav3.2 voltage-gated calcium channels, respectively. In vitro functional analysis of human Nav1.6 and Cav3.2 channel variants revealed mild but significant alterations of their gating properties that were in general consistent with a gain- and loss-of-channel function, respectively. Although additional studies will be required to confirm the actual pathogenic involvement of SCN8A and CACNA1H, these findings add to the notion that rare ion channel variants may contribute to the etiology of DEEs.
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    Identification of a molecular gating determinant within the carboxy terminal region of Cav3.3 T-type channels
    (2019-04-08) Jurkovicova-Tarabova, Bohumila; Cmarko, Leos; Rehak, Renata; Zamponi, Gerald W; Lacinova, Lubica; Weiss, Norbert
    Abstract The physiological functions controlled by T-type channels are intrinsically dependent on their gating properties, and alteration of T-type channel activity is linked to several human disorders. Therefore, it is essential to develop a clear understanding of the structural determinants responsible for the unique gating features of T-type channels. Here, we have investigated the specific role of the carboxy terminal region by creating a series a deletion constructs expressed in tsA-201 cells and analyzing them by patch clamp electrophysiology. Our data reveal that the proximal region of the carboxy terminus contains a structural determinant essential for shaping several gating aspects of Cav3.3 channels, including voltage-dependence of activation and inactivation, inactivation kinetics, and coupling between the voltage sensing and the pore opening of the channel. Altogether, our data are consistent with a model in which the carboxy terminus stabilizes the channel in a closed state.