A homozygous missense variant in CACNB4 encoding the auxiliary calcium channel beta4 subunit causes a severe neurodevelopmental disorder and impairs channel and non-channel functions

Abstract

P/Q-type channels are the principal presynaptic calcium channels in brain functioning in neurotransmitter release. They are composed of the pore-forming Ca V 2.1 α 1 subunit and the auxiliary α2δ-2 and β 4 subunits. β 4 is encoded by CACNB4, and its multiple splice variants serve isoform-specific functions as channel subunits and transcriptional regulators in the nucleus. In two siblings with intellectual disability, psychomotor retardation, blindness, epilepsy, movement disorder and cerebellar atrophy we identified rare homozygous variants in the genes LTBP1, EMILIN1, CACNB4, MINAR1, DHX38 and MYO15 by whole-exome sequencing. In silico tools, animal model, clinical, and genetic data suggest the p.(Leu126-Pro) CACNB4 variant to be likely pathogenic. To investigate the functional consequences of the CACNB4 variant, we introduced the corresponding mutation L125P into rat β 4b cDNA. Heterologously expressed wild-type β 4b associated with GFP-Ca V 1.2 and accumulated in presynaptic boutons of cultured hippocampal neurons. In contrast, the β 4b-L125P mutant failed to incorporate into calcium channel complexes and to cluster presynaptically. When co-expressed with Ca V 2.1 in tsA201 cells, β 4b and β 4b-L125P augmented the calcium current amplitudes, however, β 4b-L125P failed to stably complex with α 1 subunits. These results indicate that p.Leu125Pro disrupts the stable association of β 4b with native calcium channel complexes, whereas membrane incorporation, modulation of current density and activation properties of heterologously expressed channels remained intact. Wildtype β 4b was specifically targeted to the nuclei of quiescent excitatory cells. Importantly, the p.Leu125Pro mutation abolished nuclear targeting of β 4b in cultured myotubes and hippocampal neurons. While binding of β 4b to the known interaction partner PPP2R5D (B56δ) was not affected by the mutation, complex formation between β 4b-L125P and the neuronal TRAF2 and NCK

ubtor Mutation Causes Motor Hyperactivity by Activating mTOR Signaling in Zebrafish

“…It has also been suggested that UBTOR/ MINAR1 is implicated in Notch signaling and angiogenesis [13]. The in vivo function of UBTOR is largely unknown, except as a candidate gene in various cancers, and it has also been reported in genetic studies of neurodevelopmental disorders and intellectual disability [33]. Our results in this study showed that disruption of ubtor in zebrafish resulted in motor hyperactivity and elevated neuronal activity.…”

PPP2R5D-Related Neurodevelopmental Disorder or Developmental and Epileptic Encephalopathy?: A Novel Phenotypic Description and Review of Published Cases

“…20,24 Besides, it is involved in the targeting of subunits (like CACNB4) of voltage-gated calcium channels to the nucleus. 25 Multiple essential functions of this protein make it an important target of research.…”

“…However, its interaction with auxiliary β4 subunit of P/Q-type presynaptic calcium channel may play a role. 25,26 Nuclear translocation of CACNB4-PP2A-PPP2R5D complex regulates transcription of genes like tyrosine hydroxylase. 26 Variations in CACNB4 have been associated with episodic ataxia and epilepsies like genetic generalized epilepsies, DEE, and others.…”

Paroxysmal Genetic Movement Disorders and Epilepsy

“…EA5 is caused by mutations in the voltage-gated calcium channel encoded by the gene CACNB4 ( 30 , 171 , 172 ). Since there are only a few kindreds described, it is difficult to draw conclusions about the phenotypic spectrum.…”

“…It appears that in the heterozygous state mutations in CACNB4 lead to autosomal dominant EA5 and/or predisposition to epilepsy (particularly myoclonic and generalized types), but larger-scale human studies have not conclusively confirmed the latter ( 172 ). In the homozygous state, mutations appear cause a more severe neurodevelopmental disorder ( 171 ).…”