CACNA1C Mutations Research Articles

An induced pluripotent stem cell line (SHEHi002-A (5426))from a patient of long QT syndrome type 8 with c.2573G>A mutation in the gene CACNA1C

Long QT syndrome type 8 is an uncommon inherited condition .An induced pluripotent stem cell (iPSC) line was generated from Peripheral blood mononuclear cells (PBMCs) of a 10-year-old patient with heterozygous mutation of p.R858H(c.2573G>A)in the CACNA1C gene. This iPSC model offers a very valuable resource to study the disease pathophysiology and to develop therapeutics for treatment of Long QT syndrome type 8 patients.

An autism-causing calcium channel variant functions with selective autophagy to alter axon targeting and behavior

Common and rare variants of the CACNA1C voltage-gated calcium channel gene have been associated with autism and other neurodevelopmental disorders including schizophrenia, bipolar disorder and ADHD. However, little is known about how CACNA1C variants affect cellular processes to alter neurodevelopment. The Timothy syndrome mutation is a rare de novo gain-of-function variant in CACNA1C that causes autism with high penetrance, providing a powerful avenue into investigating the role of CACNA1C variants in neurodevelopmental disorders. Here, we use egl-19, the C. elegans homolog of CACNA1C, to investigate the role of voltage-gated calcium channels in autism. We show that an egl-19(gof) mutation that is equivalent to the Timothy syndrome mutation can alter axon targeting and affect behavior in C. elegans. We find that wildtype egl-19 negatively regulates axon termination. The egl-19(gof) mutation represses axon termination to cause axon targeting defects that lead to the misplacement of electrical synapses and alterations in habituation to light touch. Moreover, genetic interactions indicate that the egl-19(gof) mutation functions with genes that promote selective autophagy to cause defects in axon termination and behavior. These results reveal a novel genetic mechanism whereby a de novo mutation in CACNA1C can drive alterations in circuit formation and behavior.

Mutations in KIAA1109, CACNA1C, BSN, AKAP13, CELSR2, and HELZ2 Are Associated With the Prognosis in Endometrial Cancer.

Endometrial cancer (EC) is one of the most common gynecologic malignancies. Emerging studies had demonstrated the mutations in genes could serve as diagnostic or prognostic markers for human cancers. In this study, we screened mutated genes in EC and found that the mutations in KIAA1109, CACNA1C, BSN, AKAP13, CELSR2, and HELZ2 were correlated to the overall survival time in patients with EC. Bioinformatics analysis showed KIAA1109 was involved in regulating NIK/NF-kappaB signaling, CACNA1C was found to regulate cell migration and proliferation, BSN was found to regulate Wnt signaling pathway, CELSR2 was involved in regulating cell–cell adhesion, nuclear import, and protein folding, HELZ2 was found to regulate multiple immune related biological processes, and AKAP13 was involved in regulating translation, mRNA nonsense-mediated decay, rRNA processing, translational initiation, and mRNA splicing via spliceosome. The findings provided a novel therapeutic strategy in patients with EC.

P2865Mutation specific clinical characteristics in long QT syndrome type 8; severe phenotype in Timothy syndrome patients

Abstract Background Long QT syndrome type 8 (LQT8) caused by mutations in CACNA1C has been classified as a very rare and severe type of long QT syndrome accompanied with Timothy syndrome (TS) with extra-cardiac phenotype. Recently, various mutations in CACNA1C have been identified in non-TS patients. However, mutation specific severity in LQT8 has not been elucidated yet, especially for non-TS patients. Purpose We aimed to clarify the clinical characteristics of LQT8 patients. Methods The study consists of 26 LQT8 patients (21 probands and 5 family members). We evaluated their phenotype. Results Table summarizes the clinical characteristics of LQT8 patients. TS patients diagnosed in younger age than those of non-TS. Four TS and one non-TS patients were diagnosed at the age of 0, though the non-TS patient was a son of a patient and asymptomatic. Nine patients suffered symptoms including 7 with cardiac arrest. We identified three TS mutations; classical p.G406R in two and p.G402S in two, and a new TS mutation, p.412M in one. Four of TS patients were symptomatic and two died suddenly at the age of 4 and 5. In contrast, no one died in non-TS patients. Five non-TS patients suffered symptoms in the age of 4,9,15,54 and 64, and the mutations were p.S643F, p.R858H (2 patients), p.K1518E and p.K1591T. Characteristics of TS and non-TS patient TS Non-TS P N (male) 5 (2) 21 (9) Age (range) 0 (0–7) 12 (0–64) 0.004 Symptom Syncope 4 5 0.034 CPA 3 4 0.101 ECG characteristics QT interval 603±40 507±14 0.011 T wave alternans 5 2 <0.001 AV Block 4 1 0.002 Therapy (4 unknown) Beta-blocker 4 7 0.311 Mexiletine 3 1 0.024 ICD implantation 2 2 0.21 Conclusions Although TS patients showed severe phenotype, most of the non-TS patients were asymptomatic. The phenotype in LQT8 are diversely different depend on the mutations, especially between patients with TS and non-TS.

Dysfunctional Cav1.2 channel in Timothy syndrome, from cell to bedside.

Timothy syndrome is a rare disorder caused by CACNA1C gene mutations and characterized by multi-organ system dysfunctions, including ventricular arrhythmias, syndactyly, dysmorphic facial features, intermittent hypoglycemia, immunodeficiency, developmental delay, and autism. Because of the low morbidity and high mortality at a young age, it remains a huge challenge to establish a diagnosis and treatment system to manage Timothy syndrome patients. Here, we aim to provide a detailed review of Timothy syndrome, discuss the mechanisms underlying dysfunctional Cav1.2 due to CACNA1C mutations, and provide some new emerging evidences in treating Timothy syndrome from cell to bedside, promoting the management of this rare disease. Impact statement The knowledge of Timothy syndrome (TS) caused by dysfunctional Cav1.2 channel due to CACNA1C mutations is rapidly evolving as novel technologies of electrophysiology are introduced and our understanding of the mechanisms of TS develops. In this review, we focus on the TS-related dysfunctional Cav1.2 and the underlying mechanisms. We update TS-related CACNA1C mutations in a precise way over the past 20 years and summarize all reported TS patients based on their clinical presentations and molecular mechanisms, respectively. We hope this review will provide a new comprehensive way to better understand the electrophysiological mechanisms underlying TS from cell to bedside, promoting the management of TS in practice.

Effects of Cacna1c haploinsufficiency on social interaction behavior and 50-kHz ultrasonic vocalizations in adult female rats

The risk gene CACNA1C is strongly implicated in the etiology of all major psychiatric disorders, such as depressive disorder, bipolar disorder, autism spectrum disorder, and schizophrenia. These disorders feature high levels of comorbidity and share an overlap of symptoms; in particular, deficits in social functioning are common. Intriguingly, sex-dependent effects of CACNA1C single nucleotide polymorphisms on prevalence, health outcomes, and psychological traits have been reported, typically suggesting that women are more affected by CACNA1C mutations than men. In rodents, genetic modifications specifically targeting Cacna1c have repeatedly been linked to deficits in social behavior in male mice and rats but many studies neglect the sex-dependent effects observed in humans. Our study focused on the role of Cacna1c in regulating social behavior and communication in adult female rats. We compared social and non-social behavior together with concomitant emission of pro-social 50-kHz ultrasonic vocalizations (USV) associated with positive affect in constitutive heterozygous (Cacna1c+/−) rats to wildtype (Cacna1c+/+) littermate controls. Our results indicate that partial Cacna1c depletion leads to strongly reduced emission of 50-kHz USV and mild social deficits during female direct reciprocal social interaction. Detailed temporal analyses revealed most prominent reductions of 50-kHz USV during non-social behavior, suggesting that reduced positive affect occurs in a social context in Cacna1c+/− rats but is not specifically linked to social behavior. Finally, we observed increased self-grooming behavior in Cacna1c+/− rats, consistent with an autism-like phenotype. Our findings in rats thus support a role of Cacna1c in regulating behavioral phenotypes with relevance for several neuropsychiatric disorders.

<i>De Novo</i> Mutations in 124 Cases of Sudden Unexplained Deaths in Childhood

Background: Sudden unexplained death in childhood (SUDC) is an understudied public health issue with multiple potential risk factors, including undiagnosed cardiac and seizure disorders, for which genetic risk factors can contribute. Methods: We studied whole exome sequence data from 124 consecutively ascertained trios (decedent child and unaffected parents) to test for excessive de novo mutations in cardiac, epilepsy and other genes. Findings: Among SUDC decedents, nonsynonymous mutations were enriched in genes associated with cardiac and seizure disorders relative to non-sudden death controls (odds ratio=9.76, p=2.15x10-4). Beyond these genes there was a trend for excess loss-of-function mutations in genes that are loss-of-function intolerant (odds ratio=2.34, p=0.08). In our cohort, two genes had recurrent missense mutations, RYR2 and CACNA1C. Both RYR2 mutations are known as pathogenic (p=1.7x10-7). Both CACNA1C mutations are within a short (104 nucleotide) exon (p=1.0x10-7). We found evidence for over-transmission of loss-of-function or pathogenic variants within cardiac and seizure disorder genes (11/14 transmitted, p=0.03). Interpretation: Eleven of 124 (8.9%) decedents carried likely pathogenic or pathogenic variants associated with sudden death via a lethal cardiac or seizure disorder. Of these, 7 were de novo in origin, 1 was a transmitted parental mosaic mutation, and 3 were transmitted from heterozygous parents. Funding Statement: This study was supported by funding from the SUDC Foundation and Finding A Cure for Epilepsy and Seizures (NYU). RWT was supported by NIH grants R01 DA040484 and R01 MH71739. MJA and DJT were supported by the Mayo Clinic Windland Smith Rice Comprehensive Sudden Cardiac Death Program. Declaration of Interests: MJA is a consultant for Audentes Therapeutics, Boston Scientific, Gilead Sciences, Invitae, Medtronic, Myokardia, and St. Jude Medical. MJA and Mayo Clinic have an equity/royalty relationship with AliveCor, Blue Ox Health, and StemoniX. However, none of these entities are related to study. DG reports he is cofounder and holds equity in Q State – Pairnomix and Praxis Therapeutics, and equity in Apostle Inc. He receives personal fees from AstraZeneca, outside the submitted work. RT reports his participation on the Scientific Advisory boards of Howard Hughes Medical Institute, the Institute of Neuroscience (Shanghai), and the Institute of Science and Technology (Vienna). RT also reports his participation in the Actelion Scientific Advisory Board (Basel) with no compensation during 3 year span. OD reports equity interest in Empatica and receive funding from NINDS on SUDEP research. MJA, OD and PL are members of the SUDC Foundation’s scientific advisory board. LGC is President of the SUDC Foundation. MJA, OD, PL and LGC do not participate in grant funding decisions or negotiations by the SUDC Foundation to NYU Langone Health. PL, DMH, RR, XW, JP have no declarations of interests. Ethics Approval Statement: Parental consent was obtained in this NYU Institutional Review Board approved study (# S14-01061).

Refractory ventricular fibrillations after surgical repair of atrial septal defects in a patient with CACNA1C gene mutation - case report

BackgroundCongenital long QT syndrome (LQTS) can cause ventricular arrhythmic events with syncope and sudden death resulting from malignant torsades de pointes (TdP) followed by ventricular fibrillations (VFs). However, the syndrome is often overlooked prior to the development of arrhythmic events in patients with congenital heart diseases demonstrating right bundle branch block on electrocardiogram (ECG). We present a case of an adult patient with congenital heart disease who developed VFs postoperatively, potentially due to his mutation in a LQTS related gene, which was not identified on preoperative assessment due to incomplete evaluation of his family history.Case presentationA 64-year-old man was diagnosed as having multiple atrial septal defects. He presented with no symptoms of heart failure. His preoperative ECG showed complete right bundle branch block (CRBBB) with a corrected QT interval time of 478 ms. He underwent open-heart surgery to close the defects through median sternotomy access. Three hours after the operation, he developed multiple events of TdP and VFs in the intensive care unit. Cardiopulmonary resuscitation and multiple cardioversions were attempted for his repetitive TdP and VFs. He eventually reverted to sinus rhythm, and intravenous beta-blocker was administered to maintain the sinus rhythm. After this event, his family history was reviewed, and it was confirmed that his daughter and grandson had a medical history of arrhythmia. A genetic test confirmed that he had a missense mutation in CACNA1C, p.K1580 T, which is the cause for type 8.ConclusionsThis case highlights the importance of paying attention to other ECG findings in patients with CRBBB, which can mask prolonged QT intervals.

Computational Cardiac Modeling Reveals Mechanisms of Ventricular Arrhythmogenesis in Long QT Syndrome Type 8: CACNA1C R858H Mutation Linked to Ventricular Fibrillation.

Functional analysis of the L-type calcium channel has shown that the CACNA1C R858H mutation associated with severe QT interval prolongation may lead to ventricular fibrillation (VF). This study investigated multiple potential mechanisms by which the CACNA1C R858H mutation facilitates and perpetuates VF. The Ten Tusscher-Panfilov (TP06) human ventricular cell models incorporating the experimental data on the kinetic properties of L-type calcium channels were integrated into one-dimensional (1D) fiber, 2D sheet, and 3D ventricular models to investigate the pro-arrhythmic effects of CACNA1C mutations by quantifying changes in intracellular calcium handling, action potential profiles, action potential duration restitution (APDR) curves, dispersion of repolarization (DOR), QT interval and spiral wave dynamics. R858H “mutant” L-type calcium current (ICaL) augmented sarcoplasmic reticulum calcium content, leading to the development of afterdepolarizations at the single cell level and focal activities at the tissue level. It also produced inhomogeneous APD prolongation, causing QT prolongation and repolarization dispersion amplification, rendering R858H “mutant” tissue more vulnerable to the induction of reentry compared with other conditions. In conclusion, altered ICaL due to the CACNA1C R858H mutation increases arrhythmia risk due to afterdepolarizations and increased tissue vulnerability to unidirectional conduction block. However, the observed reentry is not due to afterdepolarizations (not present in our model), but rather to a novel blocking mechanism.

Altered Cav1.2 function in the Timothy syndrome mouse model produces ascending serotonergic abnormalities.

Polymorphism in the gene CACNA1C, encoding the pore-forming subunit of Cav1.2 L-type calcium channels, has one of the strongest genetic linkages to schizophrenia, bipolar disorder and major depressive disorder: psychopathologies in which serotonin signaling has been implicated. Additionally, a gain-of-function mutation in CACNA1C is responsible for the neurodevelopmental disorder Timothy syndrome that presents with prominent behavioral features on the autism spectrum. Given an emerging role for serotonin in the etiology of autism spectrum disorders (ASD), we investigate the relationship between Cav1.2 and the ascending serotonin system in the Timothy syndrome type 2 (TS2-neo) mouse, which displays behavioral features consistent with the core triad of ASD. We find that TS2-neo mice exhibit enhanced serotonin tissue content and axon innervation of the dorsal striatum, as well as decreased serotonin turnover in the amygdala. These regionally specific alterations are accompanied by an enhanced active coping response during acute stress (forced swim), serotonin neuron Fos activity in the caudal dorsal raphe, and serotonin type 1A receptor-dependent feedback inhibition of the rostral dorsal raphe nuclei. Collectively, these results suggest that the global gain-of-function Cav1.2 mutation associated with Timothy syndrome has pleiotropic effects on the ascending serotonin system including neuroanatomical changes, regional differences in forebrain serotonin metabolism and feedback regulatory control mechanisms within the dorsal raphe. Altered activity of the ascending serotonin system continues to emerge as a common neural signature across several ASD mouse models, and the capacity for Cav1.2 L-type calcium channels to impact both serotonin structure and function has important implications for several neuropsychiatric conditions.

Novel trigenic CACNA1C/DES/MYPN mutations in a family of hypertrophic cardiomyopathy with early repolarization and short QT syndrome

BackgroundHypertrophic cardiomyopathy (HCM) patients with early repolarization (ER) pattern are at higher risk of ventricular arrhythmia, yet the genetic background of this situation has not been well investigated. Here we report novel trigenic mutations detected in a Chinese family of obstructive HCM with ER and short QT syndrome (SQTS).MethodsProband and family members underwent detailed medical assessments. DNAs were extracted from peripheral blood leukocytes for genetic screening with next generation method. The functional characterization of the mutation was conducted in TSA201 cells with patch-clamp experiment.ResultsThe proband was a 52-year-old male who had a ER pattern ECG in inferioral-lateral leads with atrioventricular block and QTc of 356 ms. He also suffered from severe left ventricular hypertrophy and dysfunction. Targeted sequencing revealed trigenic mutations: c.700G>A/p.E234K in DES, c.2966G>A/p.R989H in MYPN, and c.5918G>C/p.R1973P in CACNA1C. All mutations were also detected in his daughter with ER and mild myocardium hypertrophy. The CACNA1C-R1973P mutation caused significant reduction (68.4%) of ICa compared to CACNA1C-WT (n = 14 and 14, P < 0.05). The computer modeling showed that all 3 mutations were highly disease-causing. The proband received the CRT-D (cardiac resynchronizing therapy) implantation, which lowered the left ventricular outflow tract gradient (LVOTG, 124 mmHg pre vs. 27 mmHg post) and restored the LV function (LVEF 40% pre vs. 63% post).ConclusionsThe study reveals a novel CACNA1C mutation underlying the unique ER pattern ECGs with SQTS. It also shows the rare trigenic mutations are the pathogenic substrates for the complicated clinical manifestation in HCM patients.

An Inherited Arrhythmia Syndrome with Long QT, Sudden Death and Depolarization Disorder Due to an In-Frame Deletion in Exon 16 of the CACNA1C Gene

Mutations of the gene encoding the L-type voltage gated calcium channel alpha-1C subunit (CACNA1C) underlie long QT phenotypes as part of Timothy syndrome. Milder phenotypes, as well as isolated cardiac phenotypes, including Brugada syndrome have been observed. To date, CACNA1C mutations have typically been missense mutations on limited number of sites that result in either gain of function (Timothy syndrome with a prolonged QT) or loss of function (short QT and/or Brugada pattern on ECG). We report a multiplex four-generation family with 3 individuals affected by QT prolongation, sudden cardiac death and conduction abnormalities, segregating with a novel heterozygous in-frame deletion mutation in exon 16 of CACNA1C resulting in a single amino acid deletion (p.Lys773del) discovered by using clinical gene panel testing at Invitae Corporation. Affected members are present in 3 consecutive generations (II, III and IV), and demonstrate only the cardiac rhythm phenotype segregating in an autosomal dominant fashion, with normal intellect, socialization and absence of syndactyly. The implicated in-frame deletion mutation of CACNA1C is absent from the exome aggregation consortium (ExAC) database, predicted to be disease causing by Mutation Taster, and removed an evolutionarily conserved lysine amino acid residue at position 773. Three-dimensional modelling demonstrated a marked effect of the mutation on the predicted protein structure.

Pro-arrhythmogenic effects of CACNA1C G1911R mutation in human ventricular tachycardia: insights from cardiac multi-scale models.

Mutations in the CACNA1C gene are associated with ventricular tachycardia (VT). Although the CACNA1C mutations were well identified in patients with cardiac arrhythmias, mechanisms by which cardiac arrhythmias are generated in such genetic mutation conditions remain unclear. In this study, we identified a novel mechanism of VT resulted from enhanced repolarization dispersion which is a key factor for arrhythmias in the CACNA1C G1911R mutation using multi-scale computational models of the human ventricle. The increased calcium influx in the mutation prolonged action potential duration (APD), produced steepened action potential duration restitution (APDR) curves as well as augmented membrane potential differences among different cell types during repolarization, increasing transmural dispersion of repolarization (DOR) and the spatial and temporal heterogeneity of cardiac electrical activities. Consequentially, the vulnerability to unidirectional conduction block in response to a premature stimulus increased at tissue level in the G1911R mutation. The increased functional repolarization dispersion anchored reentrant excitation waves in tissue and organ models, facilitating the initiation and maintenance of VT due to less meandering rotor tip. Thus, the increased repolarization dispersion caused by the G1911R mutation is a primary factor that may primarily contribute to the genesis of cardiac arrhythmias in Timothy Syndrome.

Calcium Revisited: New Insights Into the Molecular Basis of Long-QT Syndrome.

The first clinical description of long-QT syndrome (LQTS) occurred in 1957 when Drs Anton Jervell and Fred Lange-Nielsen postulated that syncopal/seizure episodes and high propensity for sudden cardiac death (SCD) observed in a subset of children with sensorineural deafness and otherwise unexplained heart rate–corrected QT interval prolongation on ECG stemmed from a novel congenital disorder.1 This was followed by independent descriptions of a syndrome characterized by a cardiac-only phenotype consisting of prolonged QT intervals and an increased risk for syncope, seizures, and SCD in the absence of sensorineural deafness by Drs Cesarino Romano and Owen Ward, in 1963 and 1964, respectively.2,3 During the past 5 decades, insights gleamed from a multitude of clinical, epidemiological, and molecular studies have demonstrated that LQTS is a collection of not only genetically and phenotypically diverse disorders of cardiac repolarization that encompasses the aforementioned predominantly autosomal-dominant, nonsyndromic Romano–Ward syndrome now simply referred to as LQTS4 and autosomal-recessive, multisystem, Jervell–Lange Nielsen syndrome but also exceedingly rare multisystem LQTS subtypes such as Timothy syndrome (TS) characterized by QT prolongation and an increased risk of SCD along with an array of extracardiac manifestations. Although mutations in calcium (Ca2+)-handling proteins, including the CACNA1C -encoded L-type Ca2+ channel (LTCC), RYR2 -encoded ryanodine receptor-2 intracellular calcium release channel (RyR2), and many other auxiliary interacting proteins, are central to the pathogenesis of inherited cardiac arrhythmia syndromes, such as catecholaminergic ventricular tachycardia and Brugada syndrome, until recently, the contribution of dysfunctional Ca2+ handling to the pathogenesis of LQTS was limited to the extremely rare and highly lethal multisystem TS. However, the unexpected recent discoveries of multiple nonsyndromic LQTS-causative mutations in CACNA1C ,5–7 syndromic LQTS-causative mutations in CALM1-3 -encoded Calmodulin8,9 and TRDN -encoded Triadin,10 and common genetic variation at …

Novel long QT syndrome-associated missense mutation, L762F, in CACNA1C-encoded L-type calcium channel imparts a slower inactivation tau and increased sustained and window current

BackgroundMutations in the CACNA1C-encoded L-type calcium channel have been associated with Timothy syndrome (TS) with severe QT prolongation, syndactyly, facial dysmorphisms, developmental delay, and sudden death. Recently, patients hosting CACNA1C mutations with only long QT syndrome (LQTS) have been described. We sought to identify novel variants in CACNA1C associated with either TS or LQTS, and to determine the impact of the mutation on channel function. Methods/resultsTwo probands were identified with mutations in CACNA1C, one with a TS-associated mutation, G406R, and a second with genotype-negative LQTS. Illumina HiSeq 2000 whole exome sequencing on the genotype-negative LQTS proband revealed a novel variant, CACNA1C-L762F, that co-segregated within a multi-generational family. The missense mutation localized to the DII/DIII intracellular interlinker segment of the channel in a highly conserved region in close proximity to the 6th transmembrane segment of domain II (DIIS6). Whole cell patch clamp of heterologously expressed CACNA1C-L762F in TSA201 cells demonstrated slower inactivation tau and increased sustained and window current. Comprehensive review and topological mapping of all described CACNA1C mutations revealed TS-specific hotspots localizing to the cytoplasmic aspect of 6th transmembrane segment of respective domains. Probands hosting TS mutations were associated with elevated QTc, higher prevalence of 2:1 AV block, and a younger age at presentation compared to LQTS. ConclusionsThe CACNA1C-L762F mutation is associated with development of LQTS through slower channel inactivation and increased sustained and window current. TS-associated mutations localize to specific areas of CACNA1C and are associated with a younger age at presentation, higher QTc, and 2:1 AV block than isolated LQTS-associated mutations.

Molecular and Functional Characterization of Rare CACNA1C Variants in Sudden Unexplained Death in the Young.

Perturbations in the CACNA1C-encoded L-type calcium channel α-subunit have been linked recently to heritable arrhythmia syndromes, including Timothy syndrome, Brugada syndrome, early repolarization syndrome, and long QT syndrome. These heritable arrhythmia syndromes may serve as a pathogenic basis for autopsy-negative sudden unexplained death in the young (SUDY). However, the contribution of CACNA1C mutations to SUDY is unknown. We set out to determine the spectrum, prevalence, and pathophysiology of rare CACNA1C variants in SUDY. Mutational analysis of CACNA1C was conducted in 82 SUDY cases using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct sequencing. Identified variants were engineered using site-directed mutagenesis, and heterologously expressed in TSA-201 or HEK293 cells. Two SUDY cases (2.4%) harbored functional variants in CACNA1C. The E850del and N2091S variants involve highly conserved residues and localize to the II-III linker and C-terminus, respectively. Although observed in publically available exome databases, both variants confer abnormal CaV 1.2 electrophysiological characteristics. Examination of the electrophysiological properties revealed the E850del mutation in CACNA1C led to a 95% loss-of-function in ICa , and the N2091S variant led to a 105% gain-of-function in ICa. Additionally, N2091S led to minor kinetic alterations including a -3.4 mV shift in V1/2 of activation. This study provides molecular and functional evidence that rare CACNA1C genetic variants may contribute to the underlying pathogenic basis for some cases of SUDY in either a gain or loss-of-function mechanism.

Abstract 9741: A Novel Mutation Identified in a Large Multi-Generational Family With Long QT Syndrome Reveals Distinct, Disease-Specific Mutation Hot Spots within the CACNA1C- Encoded L-type Calcium Channel

Background: Mutations in the CACNA1C-encoded L-type calcium channel have been associated with Timothy Syndrome (TS) with severe QT prolongation, cardiac hypertrophy, syndactyly, facial dysmorphisms, developmental delay, and sudden death by impaired channel inactivation and increase peak current. Recently, a small number of patients with CACNA1C mutations with only long QT syndrome (LQTS) have been described. Objective: To explore whether CACNA1C mutations associated with TS were mechanistically and clinically distinct from CACNA1C-mediated LQTS. Methods/Results: Illumina HiSeq 2000 platform-based whole exome sequencing with variant alignment using HGSC Mercury analysis and Atlas2 revealed a novel variant CACNA1C-L762F that co-segregated with affected patients of a large, multi-generational family with LQTS and sudden death. The proband presented at 3 years of age with out-of-hospital cardiac arrest and demonstrated QTc of 530. The mutation localized to the DII/DIII intracellular linker domain of the channel in a highly conserved region in close proximity to the 6th DI transmembrane domain. Whole cell patch clamp of heterologously expressed CACNA1C-L762F in TSA201 cells demonstrated slower inactivation tau and increased late current indicating its gain-of-function cellular electrophysiological phenotype. Comprehensive review and topological mapping of all described CACNA1C mutations associated with TS or LQTS revealed disease-specific hotspots. TS-associated mutations localized to cytoplasmic aspects of transmembrane domains while LQTS-associated mutations localized to cytoplasmic N- and C-terminal domains and linker regions. Probands hosting TS mutations demonstrated markedly prolonged QTc values compared to LQTS (618 vs 486 ms, p&lt;0.001) and were younger at presentation (2.7 vs 20.1 years, p&lt;0.002). Supporting these associations, the L762F mutation localized closer to the CACNA1C transmembrane domain than any other LQTS mutation and are associated with a QTc and age of diagnosis reflective of TS-associated mutations. Conclusions: The CACNA1C-L762F mutation is associated with biochemical and clinical features which highlight a molecular and clinical distinction between TS- and LQTS-associated CACNA1C mutations.

GW26-e3983 Ca2+/calmodulin-dependent protein kinase modulation of torsade de pointes arrhythmogenesis and identification of targeted sites of antiarrhythmic therapy in human Timothy Syndrome arising from a new CACNA1C mutation

GW26-e3983 Ca2+/calmodulin-dependent protein kinase modulation of torsade de pointes arrhythmogenesis and identification of targeted sites of antiarrhythmic therapy in human Timothy Syndrome arising from a new CACNA1C mutation

Identification and Functional Characterization of a Novel CACNA1C-Mediated Cardiac Disorder Characterized by Prolonged QT Intervals With Hypertrophic Cardiomyopathy, Congenital Heart Defects, and Sudden Cardiac Death.

A portion of sudden cardiac deaths can be attributed to structural heart diseases, such as hypertrophic cardiomyopathy (HCM) or cardiac channelopathies such as long-QT syndrome (LQTS); however, the underlying molecular mechanisms are distinct. Here, we identify a novel CACNA1C missense mutation with mixed loss-of-function/gain-of-function responsible for a complex phenotype of LQTS, HCM, sudden cardiac death, and congenital heart defects. Whole exome sequencing in combination with Ingenuity variant analysis was completed on 3 affected individuals and 1 unaffected individual from a large pedigree with concomitant LQTS, HCM, and congenital heart defects and identified a novel CACNA1C mutation, p.Arg518Cys, as the most likely candidate mutation. Mutational analysis of exon 12 of CACNA1C was completed on 5 additional patients with a similar phenotype of LQTS plus a personal or family history of HCM-like phenotypes and identified 2 additional pedigrees with mutations at the same position, p.Arg518Cys/His. Whole cell patch clamp technique was used to assess the electrophysiological effects of the identified mutations in CaV1.2 and revealed a complex phenotype, including loss of current density and inactivation in combination with increased window and late current. Through whole exome sequencing and expanded cohort screening, we identified a novel genetic substrate p.Arg518Cys/His-CACNA1C, in patients with a complex phenotype including LQTS, HCM, and congenital heart defects annotated as cardiac-only Timothy syndrome. Our electrophysiological studies, identification of mutations at the same amino acid position in multiple pedigrees, and cosegregation with disease in these pedigrees provide evidence that p.Arg518Cys/His is the pathogenic substrate for the observed phenotype.

Schizophrenia Related Variants in CACNA1C also Confer Risk of Autism.

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders with a strong genetic component. Many lines of evidence indicated that ASD shares common genetic variants with other psychiatric disorders (for example, schizophrenia). Previous studies detected that calcium channels are involved in the etiology of many psychiatric disorders including schizophrenia and autism. Significant association between CACNA1C (calcium channel, voltage-dependent, L type, alpha 1C subunit) and schizophrenia was detected. Furthermore, rare mutation in CACNA1C is suggested to cause Timothy syndrome, a multisystem disorder including autism-associated phenotype. However, there is no evidence for association between CACNA1C and autism in Chinese Han population. To investigate the association between single nucleotide polymorphisms (SNP) in CACNA1C and autism, we first performed a family-based association study between eighteen SNPs in CACNA1C and autism in 239 trios. All SNPs were genotyped by using Sequenom genotyping platform. Two SNPs (rs1006737 and rs4765905) have a trend of association with autism. To further confirm the association between these two SNPs with autism, we expanded the sample size to 553 trios by adding 314 trios. Association analyses for SNPs and haplotype were performed by using family-based association test (FBAT) and Haploview software. Permutation tests were used for multiple testing corrections of the haplotype analyses (n=10,000). The significance level for all statistical tests was two-tailed (p<0.05). The results demonstrated that G allele of rs1006737 and G allele of rs4765905 showed a preferential transmission to affected offspring in 553 trios (p=0.035). Haplotype analyses showed that two haplotypes constructed from rs1006737 and rs4765905 were significantly associated with autism (p=0.030, 0.023, respectively; Global p=0.046). These results were still significant after permutation correction (n=10,000, p=0.027). Our research suggests that CACNA1C might play a role in the genetic etiology of autism in Chinese Han population.