A Cross-Sectional Study of the Neuropsychiatric Phenotype of CACNA1C-Related Disorder

Alternative splicing in autism spectrum disorder: Recent insights from mechanisms to therapy

Alternative splicing (AS) is a vital and highly dynamic RNA regulatory mechanism that allows a single gene to generate multiple mRNA and protein isoforms. Dysregulation of AS has been identified as a key contributor to the pathogenesis of autism spectrum disorders (ASD). A comprehensive understanding of aberrant splicing mechanisms and their functional consequences in ASD can help uncover the molecular basis of the disorder and facilitate the development of therapeutic strategies. This review focuses on the major aberrant splicing events and key splicing regulators associated with ASD, highlighting their roles in linking defective splicing to ASD pathogenesis. In addition, a discussion of how emerging technologies, such as long-read sequencing, single-cell sequencing, spatial transcriptomics and CRISPR-Cas systems are offering novel insights into the role and mechanisms of AS in ASD is presented. Finally, the RNA splicing-based therapeutic strategies are evaluated, emphasizing their potential to address unmet clinical needs in ASD treatment.

Functional characterization of a novel de novo CACNA1C pathogenic variant in a patient with neurodevelopmental disorder

Mutations in CACNA1C, the gene encoding Cav1.2 voltage-gated calcium channels, are associated with a spectrum of disorders, including Timothy syndrome and other neurodevelopmental and cardiac conditions. In this study, we report a child with a de novo heterozygous missense variant (c.1973T > C; L658P) in CACNA1C, presenting with refractory epilepsy, global developmental delay, hypotonia, and multiple systemic abnormalities, but without overt cardiac dysfunction. Electrophysiological analysis of the recombinant Cav1.2 L658P variant revealed profound gating alterations, most notably a significant hyperpolarizing shift in the voltage dependence of activation and inactivation. Additionally, molecular modeling suggested that the L658P mutation disrupts interactions within the IIS5 transmembrane segment, reducing the energy barrier for state transitions and facilitating channel opening at more negative voltages. These findings establish L658P as a pathogenic CACNA1C variant primarily associated with severe neurological dysfunction and expands the phenotypic spectrum of CACNA1C-related disorders.

Inactivation of CaV1 and CaV2 channels

Voltage-gated Ca2+ channels (VGCCs) are highly expressed throughout numerous biological systems and play critical roles in synaptic transmission, cardiac excitation, and muscle contraction. To perform these various functions, VGCCs are highly regulated. Inactivation comprises a critical mechanism controlling the entry of Ca2+ through these channels and constitutes an important means to regulate cellular excitability, shape action potentials, control intracellular Ca2+ levels, and contribute to long-term potentiation and depression. For CaV1 and CaV2 channel families, inactivation proceeds via two distinct processes. Voltage-dependent inactivation (VDI) reduces Ca2+ entry through the channel in response to sustained or repetitive depolarization, while Ca2+-dependent inactivation (CDI) occurs in response to elevations in intracellular Ca2+ levels. These processes are critical for physiological function and undergo exquisite fine-tuning through multiple mechanisms. Here, we review known determinants and modulatory features of these two critical forms of channel regulation and their role in normal physiology and pathophysiology.

Expanding the Phenotype of the CACNA1C-Associated Neurological Disorders in Children: Systematic Literature Review and Description of a Novel Mutation

Background: CACNA1C gene encodes the alpha 1 subunit of the CaV1.2 L-type Ca2+ channel. Pathogenic variants in this gene have been associated with cardiac rhythm disorders such as long QT syndrome, Brugada syndrome and Timothy syndrome. Recent evidence has suggested the possible association between CACNA1C mutations and neurologically-isolated (in absence of cardiac involvement) phenotypes in children, giving birth to a wider spectrum of CACNA1C-related clinical presentations. However, to date, little is known about the variety of both neurological and non-neurological signs/symptoms in the neurologically-predominant phenotypes. Methods and Results: We conducted a systematic review of neurologically-predominant presentations without cardiac conduction defects, associated with CACNA1C mutations. We also reported a novel de novo missense pathogenic variant in the CACNA1C gene of a children patient presenting with constructional, dressing and oro-buccal apraxia associated with behavioral abnormalities, mild intellectual disability, dental anomalies, gingival hyperplasia and mild musculoskeletal defects, without cardiac conduction defects. Conclusions: The present study highlights the importance of considering the investigation of the CACNA1C gene in children's neurological isolated syndromes, and expands the phenotype of the CACNA1C related conditions. In addition, the present study highlights that, even in absence of cardiac conduction defects, nuanced clinical manifestations of the Timothy syndrome (e.g., dental and gingival defects) could be found. These findings suggest the high variable expressivity of the CACNA1C gene and remark that the absence of cardiac involvement should not mislead the diagnosis of a CACNA1C related disorder.

Antisense oligonucleotide therapeutic approach for Timothy syndrome

Timothy syndrome (TS) is a severe, multisystem disorder characterized by autism, epilepsy, long-QT syndrome and other neuropsychiatric conditions1. TS type 1 (TS1) is caused by a gain-of-function variant in the alternatively spliced and developmentally enriched CACNA1C exon 8A, as opposed to its counterpart exon 8. We previously uncovered several phenotypes in neurons derived from patients with TS1, including delayed channel inactivation, prolonged depolarization-induced calcium rise, impaired interneuron migration, activity-dependent dendrite retraction and an unanticipated persistent expression of exon 8A2-6. We reasoned that switching CACNA1C exon utilization from 8A to 8 would represent a potential therapeutic strategy. Here we developed antisense oligonucleotides (ASOs) to effectively decrease the inclusion of exon 8A in human cells both in vitro and, following transplantation, in vivo. We discovered that the ASO-mediated switch from exon 8A to 8 robustly rescued defects in patient-derived cortical organoids and migration in forebrain assembloids. Leveraging a transplantation platform previously developed7, we found that a single intrathecal ASO administration rescued calcium changes and in vivo dendrite retraction of patient neurons, suggesting that suppression of CACNA1C exon 8A expression is a potential treatment for TS1. Broadly, these experiments illustrate how a multilevel, in vivo and in vitro stem cell model-based approach can identify strategies to reverse disease-relevant neural pathophysiology.

Rare genetic brain disorders with overlapping neurological and psychiatric phenotypes

Understanding rare genetic brain disorders with overlapping neurological and psychiatric phenotypes is of increasing importance given the potential for developing disease models that could help to understand more common, polygenic disorders. However, the traditional clinical boundaries between neurology and psychiatry result in frequent segregation of these disorders into distinct silos, limiting cross-specialty understanding that could facilitate clinical and biological advances. In this Review, we highlight multiple genetic brain disorders in which neurological and psychiatric phenotypes are observed, but for which in-depth, cross-spectrum clinical phenotyping is rarely undertaken. We describe the combined phenotypes observed in association with genetic variants linked to epilepsy, dystonia, autism spectrum disorder and schizophrenia. We also consider common underlying mechanisms that centre on synaptic plasticity, including changes to synaptic and neuronal structure, calcium handling and the balance of excitatory and inhibitory neuronal activity. Further investigation is needed to better define and replicate these phenotypes in larger cohorts, which would help to gain greater understanding of the pathophysiological mechanisms and identify common therapeutic targets.