Congenital ataxia and hemiplegic migraine with cerebral edema associated with a novel gain of function mutation in the calcium channel CACNA1A

A Longitudinal Exploration of CACNA1A -related Hemiplegic Migraine in Children

Introduction

Since the initial description of CACNA1A- related hemiplegic migraine (HM), the phenotypic spectrum has expanded from mild episodes in neurotypical individuals to potentially life-threatening events frequently seen in individuals with developmental and epileptic encephalopathies. However, the overall longitudinal course throughout childhood remains unknown.

Methods

We analyzed HM and seizure history in individuals with CACNA1A -related HM, delineating frequency and severity of events in monthly increments through a standardized approach. Combining these data with medication prescription information, we assessed the response of HM to different agents.

Results

Our cohort involved 15 individuals between 3 and 29 years (163 patient years) and included 11 unique and two recurrent variants (p.R1349Q and p.V1393M; both n= 2). The age of first confirmed HM ranged from 14 months to 13 years (average 3 years). 25% of all HM events were severe (lasting >3 days) and 73% of individuals had at least 1 severe occurrence. Spacing of HM events ranged from 1 month to 14 years and changes in HM severity over time of showed increases or decreases of >2 severity levels in 12/122 events. Eight individuals had epilepsy, but severity of epilepsy did not correlate with frequency and severity of HM events. While levetiracetam ( n= 6) and acetazolamide ( n= 5) were the most frequently used medications, they did not show efficacy in HM prevention or HM severity reduction. However, verapamil ( n= 3) showed efficacy in preventing HM episodes (OR 2.68, CI 1.39-5.67).

Significance

The longitudinal course of CACNA1A -related HM lacks recognizable patterns for timing and severity of HM events or correlation with seizure patterns. Our data underscores the unpredictability of CACNA1A -related HM, highlighting the need for close surveillance for reoccurring HM events even in individuals with symptom-free periods.

Key points

24% of hemiplegic migraines (HM) in CACNA1A- related disorders are severe, involving cerebral edema and greater than 4 days to recover Timing and severity of HM are unpredictable, with large changes in severity between events, and age of onset ranging from 1-13 yearsEpilepsy occurred in 53% of individuals, with neither the timing nor severity of seizures correlated with HM.

Benign Paroxysmal Torticollis

BACKGROUND

The purpose of this review is to clarify the natural course of benign paroxysmal torticollis (BPT) and update the information on the relationship of this disorder with migraine. BPT belongs to a group of "episodic syndromes that may be associated with migraine" and is diagnosed according to diagnostic criteria of the International Classification of Headache Disorders, 3rd edition. BPT affects infants and young children and is often an underdiagnosed manifestation since it is not recognized in cases with a benign evolution, requiring a careful differential diagnosis. It was first described by Snyder in 1969 as a movement disorder, a cervical dystonia consequent to labyrinthic disorder.

MATERIALS AND METHODS

The PubMed and Web of Science databases were consulted from 1968 to 2024, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines.

RESULTS

In total, 113 articles were identified, 86 selected, and 25 considered for the purpose of this review. Clinical studies were considered in relation to evolution, cognitive, and motor development; genetic and not genetic etiology; the relationship with migraine with and without aura; vestibular migraine; hemiplegic migraine; and paroxysmal vertigo.

Two pediatric patients with hemiplegic migraine presenting as acute encephalopathy: case reports and a literature review

Introduction

Hemiplegic migraine (HM) is a rare subtype of migraine. HM in children may be atypical in the initial stage of the disease, which could easily lead to misdiagnosis.

Methods

We report two cases of atypical hemiplegic migraine that onset as an acute encephalopathy. And a comprehensive search was performed using PubMed, Web of Science, and Scopus. We selected only papers that reported complete clinical information about the patients with CACNA1A or ATP1A2 gene mutation.

Results

Patient #1 showed a de novo mutation, c.674C>A (p. Pro225His), in exon 5 of the CACNA1A gene. And patient #2 showed a missense mutation (c.2143G>A, p. Gly715Arg) in exon 16 of the ATP1A2. Together with our two cases, a total of 160 patients (73 CACNA1A and 87 ATP1A2) were collected and summarized finally.

Discussion

Acute encephalopathy is the main manifestation of severe attacks of HM in children, which adds to the difficulty of diagnosis. Physicians should consider HM in the differential diagnosis of patients presenting with somnolence, coma, or convulsion without structural, epileptic, infectious, or inflammatory explanation. When similar clinical cases appear, gene detection is particularly important, which is conducive to early diagnosis and treatment. Early recognition and treatment of the disease can help improve the prognosis.

The genotype-phenotype correlations of the CACNA1A-related neurodevelopmental disorders: a small case series and literature reviews

BACKGROUND

Genotype-phenotype correlations of the CACNA1A-related neurodevelopmental disorders such as global developmental delay (GDD)/intellectual disability (ID), epileptic encephalopathy (EE), and autism spectrum disorder (ASD) are unknown. We aimed to summarize genotype-phenotype correlations and potential treatment for CACNA1A-related neurodevelopmental disorders.

METHODS

Six children diagnosed with CACNA1A-related neurodevelopmental disorders at Xiangya Hospital, Central South University from April 2018 to July 2021 were enrolled. The PubMed database was systematically searched for all reported patients with CACNA1A-related neurodevelopmental disorders until February 2023. Thereafter, we divided patients into several groups for comparison.

RESULTS

Six patients were recruited from our hospital. Three cases presented with epilepsy, five with GDD/ID, five with ataxia, and two with ASD. The variants included p.G701R, p.R279C, p.D1644N, p.Y62C, p.L1422Sfs*8, and p. R1664Q [two gain-of-function (GOF) and four loss-of-function (LOF) variants]. About 187 individuals with GDD/ID harboring 123 variants were found (case series plus data from literature). Of those 123 variants, p.A713T and p.R1664* were recurrent, 37 were LOF, and 7 were GOF. GOF variants were linked with severe-profound GDD/ID while LOF variants were associated with mild-moderate GDD/ID (p = 0.001). The p.A713T variant correlated with severe-profound GDD/ID (p = 0.003). A total of 130 epileptic patients harboring 83 variants were identified. The epileptic manifestations included status epilepticus (n = 64), provoked seizures (n = 49), focal seizures (n = 37), EE (n = 29), absence seizures (n = 26), and myoclonic seizures (n = 10). About 49 (42.20%) patients had controlled seizures while 67 (57.80%) individuals remained with refractory seizures. Status epilepticus correlated with variants located on S4, S5, and S6 (p = 0.000). Among the 83 epilepsy-related variants, 23 were recurrent, 32 were LOF, and 11 were GOF. Status epilepticus was linked with GOF variants (p = 0.000). LOF variants were associated with absence seizures (p = 0.000). Six patients died at an early age (3 months to ≤5 years). We found 18 children with ASD. Thirteen variants including recurrent ones were identified in those 18 cases. GOF changes were more linked to ASD.

CONCLUSION

The p.A713T variant is linked with severe-profound GDD/ID. More than half of CACNA1A-related epilepsy is refractory. The most common epileptic manifestation is status epilepticus, which correlates with variants located on S4, S5, and S6.

Disruption of mitochondrial and lysosomal functions by human CACNA1C variants expressed in HEK 293 and CHO cells

Objective

To investigate the pathogenesis of three novel de novo CACNA1C variants (p.E411D, p.V622G, and p.A272V) in causing neurodevelopmental disorders and arrhythmia.

Methods

Several molecular experiments were carried out on transfected human embryonic kidney 293 (HEK 293) and Chinese hamster ovary (CHO) cells to explore the effects of p.E411D, p.V622G, and p.A272V variants on electrophysiology, mitochondrial and lysosomal functions. Electrophysiological studies, RT-qPCR, western blot, apoptosis assay, mito-tracker fluorescence intensity, lyso-tracker fluorescence intensity, mitochondrial calcium concentration test, and cell viability assay were performed. Besides, reactive oxygen species (ROS) levels, ATP levels, mitochondrial copy numbers, mitochondrial complex I, II, and cytochrome c functions were measured.

Results

The p.E411D variant was found in a patient with attention deficit-hyperactive disorder (ADHD), and moderate intellectual disability (ID). This mutant demonstrated reduced calcium current density, mRNA, and protein expression, and it was localized in the nucleus, cytoplasm, lysosome, and mitochondria. It exhibited an accelerated apoptosis rate, impaired autophagy, and mitophagy. It also demonstrated compromised mitochondrial cytochrome c oxidase, complex I, and II enzymes, abnormal mitochondrial copy numbers, low ATP levels, abnormal mitochondria fluorescence intensity, impaired mitochondrial fusion and fission, and elevated mitochondrial calcium ions. The p.V622G variant was identified in a patient who presented with West syndrome and moderate global developmental delay. The p.A272V variant was found in a patient who presented with epilepsy and mild ID. Both mutants (p.V622G and p.A272V) exhibited reduced calcium current densities, decreased mRNA and protein expressions, and they were localized in the nucleus, cytoplasm, lysosome, and mitochondria. They exhibited accelerated apoptosis and proliferation rates, impaired autophagy, and mitophagy. They also exhibited abnormal mitochondrial cytochrome c oxidase, complex I and II enzymes, abnormal mitochondrial copy numbers, low ATP, high ROS levels, abnormal mitochondria fluorescence intensity, impaired mitochondrial fusion and fission, as well as elevated mitochondrial calcium ions.

Conclusion

The p.E411D, p.V622G and p.A272V mutations of human CACNA1C reduce the expression level of CACNA1C proteins, and impair mitochondrial and lysosomal functions. These effects induced by CACNA1C variants may contribute to the pathogenesis of CACNA1C-related disorders.

Hemiplegic Migraine in Children and Adolescents

BACKGROUND

Only a few studies have focused on hemiplegic migraine (HM) in children despite its early age of onset. The aim of this review is to describe the peculiar characteristics of pediatric HM.

METHODS

This is a narrative review based on 14 studies on pediatric HM selected from 262 papers.

RESULTS

Different from HM in adults, pediatric HM affects both genders equally. Early transient neurological symptoms (prolonged aphasia during a febrile episode, isolated seizures, transient hemiparesis, and prolonged clumsiness after minor head trauma) can precede HM long before its onset. The prevalence of non-motor auras among children is lower than it is in adults. Pediatric sporadic HM patients have longer and more severe attacks compared to familial cases, especially during the initial years after disease onset, while familial HM cases tend to have the disease for longer. During follow-up, the frequency, intensity, and duration of HM attacks often decrease. The outcome is favorable in most patients; however, neurological conditions and comorbidities can be associated.

CONCLUSION

Further studies are needed to better define the clinical phenotype and the natural history of pediatric HM and to refine genotype-phenotype correlations in order to improve the knowledge on HM physiopathology, diagnosis, and outcome.

Concomitant Calcium Channelopathies Involving CACNA1A and CACNA1F: A Case Report and Review of the Literature

Calcium channels are an integral component in maintaining cellular function. Alterations may lead to channelopathies, primarily manifested in the central nervous system. This study describes the clinical and genetic features of a unique 12-year-old boy harboring two congenital calcium channelopathies, involving the CACNA1A and CACNA1F genes, and provides an unadulterated view of the natural history of sporadic hemiplegic migraine type 1 (SHM1) due to the patient's inability to tolerate any preventative medication. The patient presents with episodes of vomiting, hemiplegia, cerebral edema, seizure, fever, transient blindness, and encephalopathy. He is nonverbal, nonambulatory, and forced to have a very limited diet due to abnormal immune responses. The SHM1 manifestations apparent in the subject are consistent with the phenotype described in the 48 patients identified as part of a systematic literature review. The ocular symptoms of CACNA1F align with the family history of the subject. The presence of multiple pathogenic variants make it difficult to identify a clear phenotype-genotype correlation in the present case. Moreover, the detailed case description and natural history along with the comprehensive review of the literature contribute to the understanding of this complex disorder and point to the need for comprehensive clinical assessments of SHM1.

Prolonged neurologic deficits with brain MRI changes following ECT in an adolescent with a CACNA1a-related disorder; a case report

BACKGROUND

Electroconvulsive therapy is used to treat depression and schizophrenia with infrequent use in pediatric patients. We report a case of an adolescent with autism spectrum disorder and acute catatonia that presented with status epilepticus (SE) and prolonged neurologic deficits with unilateral left cerebral edema on imaging following unilateral electroconvulsive therapy (ECT) on the right side, subsequently found to have a CACNA1a pathogenic variant. This case highlights a potential adverse effect of ECT in patients with CACNA1a related disorders.

CASE

The patient received unilateral ECT to the right side and subsequently had an episode of SE with right-sided hemiplegia for 72 h prior to regaining some function with persistent mild right-hand weakness that persisted for at least 1-2 weeks. A brain MRI 2 days after ECT was unremarkable, but a repeat MRI on day four of admission showed left hemisphere cortical diffusion restriction, increased perfusion and T2 prolongation suggestive of cortical edema. They had whole exome genetic testing sent after discharge that showed a known pathogenic CACNA1a variant (p.I1709T). CACNA1a encodes the P/Q type calcium channels and deleterious variants in this gene result in a channelopathy associated with a spectrum of neurodevelopmental disorders that include autism spectrum disorder, hemiplegic migraine with unilateral cerebral edema, epileptic encephalopathies, or episodic ataxia syndromes.

CONCLUSION

A literature review of ECT and neurologic deficits showed that most neurologic deficits resolve within 30 min of ECT. Case reports of prolonged deficits are rare and there are no prior reports of acute MRI changes related to ECT. Thus, the acute deterioration and MRI findings in this patient are likely related to the underlying CACNA1a channelopathy disorder with ECT as a precipitating event. This case report suggests care should be taken when using ECT in patients with pathogenic variants in CACNA1a. Furthermore, it reinforces the utility and importance of expanded genetic testing in patients with neurodevelopmental disorders as findings can provide valuable information that can guide treatment decisions.

The complexities of CACNA1A in clinical neurogenetics

Variants in CACNA1A are classically related to episodic ataxia type 2, familial hemiplegic migraine type 1, and spinocerebellar ataxia type 6. Over the years, CACNA1A has been associated with a broader spectrum of phenotypes. Targeted analysis and unbiased sequencing of CACNA1A result not only in clear molecular diagnoses, but also in large numbers of variants of uncertain significance (VUS), or likely pathogenic variants with a phenotype that does not directly match the CACNA1A spectrum. Over the last years, targeted and clinical exome sequencing in our center has identified 41 CACNA1A variants. Ultimately, variants were considered pathogenic or likely pathogenic in 23 cases, with most phenotypes ranging from episodic or progressive ataxia to more complex ataxia syndromes, as well as intellectual disability and epilepsy. In two cases, the causality of the variant was discarded based on non-segregation or an alternative diagnosis. In the remaining 16 cases, the variant was classified as uncertain, due to lack of opportunities for segregation analysis or uncertain association with a non-classic phenotype. Phenotypic variability and the large number of VUS make CACNA1A a challenging gene for neurogenetic diagnostics. Accessible functional read-outs are clearly needed, especially in cases with a non-classic phenotype.

Biallelic variants in genes previously associated with dominant inheritance: CACNA1A, RET and SLC20A2

A subset of families with co-dominant or recessive inheritance has been described in several genes previously associated with dominant inheritance. Those recessive families displayed similar, more severe, or even completely different phenotypes to their dominant counterparts. We report the first patients harboring homozygous disease-related variants in three genes that were previously associated with dominant inheritance: a loss-of-function variant in the CACNA1A gene and two missense variants in the RET and SLC20A2 genes, respectively. All patients presented with a more severe clinical phenotype than the corresponding typical dominant form. We suggest that co-dominant or recessive inheritance for these three genes could explain the phenotypic differences from those documented in their cognate dominant phenotypes. Our results reinforce that geneticists should be aware of the possible different forms of inheritance in genes when WES variant interpretation is performed. We also evidence the need to refine phenotypes and inheritance patterns associated with genes in order to avoid failures during WES analysis and thus, raising the WES diagnostic capacity in the benefit of patients.

Mutations in the Voltage Dependent Calcium Channel CACNA1A (P/Q type alpha 1A subunit) Causing Neurological Disorders - An Overview

Background

The voltage-dependent calcium channel α1 subunit (CACNA1A) gene plays a major role in neuronal communication. Mutation in this gene results in altered Ca²⁺ ion influx that modify the neurotransmitter release resulting in the development of various neurological disorders like hemiplegic migraine with cortical spreading depression, epilepsy, episodic ataxia type 2, and spinocerebellar ataxia type 6.

Objective

This review aimed in portraying the frequent mutations in CACNA1A gene causing hemiplegic migraine with cortical spreading depression, epilepsy, episodic ataxia type 2 and spinocerebellar ataxia type 6.

Methodology

A systematic search has been adopted in various databases using the keywords "Calcium channel," "migraine," "epilepsy," "episodic ataxia," and "spinocerebellar ataxia" for writing this review that collectively focuses on mutations in the CACNA1A gene causing the common neurological diseases from 1975 to 2019.

Conclusion

Every type of mutation has its own signature in gene functioning and understanding them might aid knowing more in disease progression.

CACNA1A-associated epilepsy: Electroclinical findings and treatment response on seizures in 18 patients

CACNA1A pathogenic mutations are involved in various neurological phenotypes including episodic ataxia (EA2), spinocerebellar ataxia (SCA6), and familial hemiplegic migraine (FHM1). Epilepsy is poorly documented. We studied 18 patients (10 males) carrying de novo or inherited CACNA1A mutations, with median age of 2,5 years at epilepsy onset. Eight mutations were novel. Two variants known leading to gain of function (GOF) were found in 5 patients. Five other patients had non-sense variants leading to loss of function (LOF). Seizures were most often revealed by either status epilepticus (SE) (n = 8), eventually triggered by fever (n = 5), or absences/behavioural arrests (n = 7). Non-epileptic paroxysmal events were frequent and consisted in recurrent hemiplegic accesses (n = 9), jitteriness in the neonatal period (n = 6), and ocular paroxysmal events (n = 9). Most of the patients had early permanent cerebellar dysfunction (n = 16) and early moderate to severe global developmental delay (GDD)/intellectual deficiency (ID) (n = 17). MRI was often abnormal, with cerebellar (n = 8) and/or cerebral (n = 6) atrophy. Stroke-like occurred in 2 cases. Some antiepileptic drugs including topiramate, levetiracetam, lamotrigine and valproate were effective on seizures. Acetazolamide and calcium channel blockers were often effective when used. More than half of the patients had refractory epilepsy. CACNA1A mutation should be evoked in front of 2 main electro-clinical phenotypes that are associated with permanent cerebellar dysfunction and moderate to severe GDD/ID. The first one, found in all 5 patients with GOF variants, is characterized by intractable seizures, early and recurrent SE and hemiplegic accesses. The second, less severe, found in 5 patients with LOF variants, is characterized by refractory early onset absence seizures.

Calcium channelopathies and intellectual disability: a systematic review

BACKGROUND

Calcium ions are involved in several human cellular processes including corticogenesis, transcription, and synaptogenesis. Nevertheless, the relationship between calcium channelopathies (CCs) and intellectual disability (ID)/global developmental delay (GDD) has been poorly investigated. We hypothesised that CCs play a major role in the development of ID/GDD and that both gain- and loss-of-function variants of calcium channel genes can induce ID/GDD. As a result, we performed a systematic review to investigate the contribution of CCs, potential mechanisms underlying their involvement in ID/GDD, advancements in cell and animal models, treatments, brain anomalies in patients with CCs, and the existing gaps in the knowledge. We performed a systematic search in PubMed, Embase, ClinVar, OMIM, ClinGen, Gene Reviews, DECIPHER and LOVD databases to search for articles/records published before March 2021. The following search strategies were employed: ID and calcium channel, mental retardation and calcium channel, GDD and calcium channel, developmental delay and calcium channel.

MAIN BODY

A total of 59 reports describing 159 cases were found in PubMed, Embase, ClinVar, and LOVD databases. Variations in ten calcium channel genes including CACNA1A, CACNA1C, CACNA1I, CACNA1H, CACNA1D, CACNA2D1, CACNA2D2, CACNA1E, CACNA1F, and CACNA1G were found to be associated with ID/GDD. Most variants exhibited gain-of-function effect. Severe to profound ID/GDD was observed more for the cases with gain-of-function variants as compared to those with loss-of-function. CACNA1E, CACNA1G, CACNA1F, CACNA2D2 and CACNA1A associated with more severe phenotype. Furthermore, 157 copy number variations (CNVs) spanning calcium genes were identified in DECIPHER database. The leading genes included CACNA1C, CACNA1A, and CACNA1E. Overall, the underlying mechanisms included gain- and/ or loss-of-function, alteration in kinetics (activation, inactivation) and dominant-negative effects of truncated forms of alpha1 subunits. Forty of the identified cases featured cerebellar atrophy. We identified only a few cell and animal studies that focused on the mechanisms of ID/GDD in relation to CCs. There is a scarcity of studies on treatment options for ID/GDD both in vivo and in vitro.

CONCLUSION

Our results suggest that CCs play a major role in ID/GDD. While both gain- and loss-of-function variants are associated with ID/GDD, the mechanisms underlying their involvement need further scrutiny.

CACNA1A Mutations Causing Early Onset Ataxia: Profiling Clinical, Dysmorphic and Structural-Functional Findings

The CACNA1A gene encodes the pore-forming α_1A subunit of the voltage-gated Ca_V2.1 Ca²⁺ channel, essential in neurotransmission, especially in Purkinje cells. Mutations in CACNA1A result in great clinical heterogeneity with progressive symptoms, paroxysmal events or both. During infancy, clinical and neuroimaging findings may be unspecific, and no dysmorphic features have been reported. We present the clinical, radiological and evolutionary features of three patients with congenital ataxia, one of them carrying a new variant. We report the structural localization of variants and their expected functional consequences. There was an improvement in cerebellar syndrome over time despite a cerebellar atrophy progression, inconsistent response to acetazolamide and positive response to methylphenidate. The patients shared distinctive facial gestalt: oval face, prominent forehead, hypertelorism, downslanting palpebral fissures and narrow nasal bridge. The two α_1A affected residues are fully conserved throughout evolution and among the whole human Ca_V channel family. They contribute to the channel pore and the voltage sensor segment. According to structural data analysis and available functional characterization, they are expected to exert gain- (F1394L) and loss-of-function (R1664Q/R1669Q) effect, respectively. Among the CACNA1A-related phenotypes, our results suggest that non-progressive congenital ataxia is associated with developmental delay and dysmorphic features, constituting a recognizable syndromic neurodevelopmental disorder.

Sporadic Hemiplegic Migraine Type 1 and Congenital Ataxia due to a Single Amino Acid Deletion (ΔF1502) in CACNA1A: A Challenging Diagnosis

Mutations in the CACNA1A gene have been classically related to three neurologic disorders: hemiplegic migraine type 1 (both familiar and sporadic FHM1/SHM1), episodic ataxia type 2 (EA2), and spinocerebellar ataxia type 6 (SCA6). More recently, pathogenic variants in CACNA1A have been recognized as causative of an early-onset cerebellar syndrome consistent with the definition of congenital ataxia (CA), variably associated with paroxysmal symptoms. Early recognition of congenital ataxia is challenging because the presenting symptoms, such as hypotonia, weak deep tendon reflexes, and delayed motor milestones, are unspecific while clear signs of a cerebellar syndrome which are usually not seen before the second or third year. Here, we report on a case of nonepisodic ataxia of congenital onset and severe SHM1 where the diagnosis of congenital ataxia was made retrospectively after the identification of the ΔF1502 pathogenic variant in CACNA1A by an hemiplegic migraine multigene panel, conducted for the onset of hemiplegic migraine attacks associated with hemispheric swelling. A significant reduction in migraine attacks frequency was achieved with acetazolamide.

The de novo CACNA1A pathogenic variant Y1384C associated with hemiplegic migraine, early onset cerebellar atrophy and developmental delay leads to a loss of Cav2.1 channel function

CACNA1A pathogenic variants have been linked to several neurological disorders including familial hemiplegic migraine and cerebellar conditions. More recently, de novo variants have been associated with severe early onset developmental encephalopathies. CACNA1A is highly expressed in the central nervous system and encodes the pore-forming Ca_Vα₁ subunit of P/Q-type (Cav2.1) calcium channels. We have previously identified a patient with a de novo missense mutation in CACNA1A (p.Y1384C), characterized by hemiplegic migraine, cerebellar atrophy and developmental delay. The mutation is located at the transmembrane S5 segment of the third domain. Functional analysis in two predominant splice variants of the neuronal Cav2.1 channel showed a significant loss of function in current density and changes in gating properties. Moreover, Y1384 variants exhibit differential splice variant-specific effects on recovery from inactivation. Finally, structural analysis revealed structural damage caused by the tyrosine substitution and changes in electrostatic potentials.

The electrophysiological footprint of CACNA1A disorders

Objectives

CACNA1A variants underlie three neurological disorders: familial hemiplegic migraine type 1 (FHM1), episodic ataxia type 2 (EA2) and spinocerebellar ataxia type 6 (SCA6). EEG is applied to study their episodic manifestations, but findings in the intervals did not gain attention up to date.

Methods

We analyzed repeated EEG recordings performed between 1994 and 2019 in a large cohort of genetically confirmed CACNA1A patients. EEG findings were compared with those of CACNA1A-negative phenocopies. A review of the related literature was performed.

Results

85 EEG recordings from 38 patients (19 EA2, 14 FHM1, 5 SCA6) were analyzed. Baseline EEG was abnormal in 55% of cases (12 EA2, 9 FHM1). The most common finding was a lateralized intermittent slowing, mainly affecting the temporal region. Slowing was more pronounced after a recent attack but was consistently detected in the majority of patients also during the follow-up. Interictal epileptic discharges (IEDs) were detected in eight patients (7 EA2,1 FHM1). EEG abnormalities and especially IEDs were significantly associated with younger age at examination (16 ± 9 vs 43 ± 21 years in those without epileptic changes, p = 0.003) and with earlier onset of disease (1 (1–2) vs 12 (5–45) years, p = 0.0009). EEG findings in CACNA1A-negative phenocopies (n = 15) were largely unremarkable (p = 0.03 in the comparison with CACNA1A patients).

Conclusions

EEG abnormalities between attacks are highly prevalent in episodic CACNA1A disorders and especially associated with younger age at examination and earlier disease onset. Our findings underpin an age-dependent effect of CACNA1A variants, with a more severe impairment when P/Q channel dysfunction manifests early in life.

Episodic Ataxias: Faux or Real?

The term Episodic Ataxias (EA) was originally used for a few autosomal dominant diseases, characterized by attacks of cerebellar dysfunction of variable duration and frequency, often accompanied by other ictal and interictal signs. The original group subsequently grew to include other very rare EAs, frequently reported in single families, for some of which no responsible gene was found. The clinical spectrum of these diseases has been enormously amplified over time. In addition, episodes of ataxia have been described as phenotypic variants in the context of several different disorders. The whole group is somewhat confused, since a strong evidence linking the mutation to a given phenotype has not always been established. In this review we will collect and examine all instances of ataxia episodes reported so far, emphasizing those for which the pathophysiology and the clinical spectrum is best defined.

Diagnostic and therapeutic aspects of hemiplegic migraine

Hemiplegic migraine (HM) is a clinically and genetically heterogeneous condition with attacks of headache and motor weakness which may be associated with impaired consciousness, cerebellar ataxia and intellectual disability. Motor symptoms usually last <72 hours and are associated with visual or sensory manifestations, speech impairment or brainstem aura. HM can occur as a sporadic HM or familiar HM with an autosomal dominant mode of inheritance. Mutations in CACNA1A, ATP1A2 and SCN1A encoding proteins involved in ion transport are implicated. The pathophysiology of HM is close to the process of typical migraine with aura, but appearing with a lower threshold and more severity. We reviewed epidemiology, clinical presentation, diagnostic assessment, differential diagnosis and treatment of HM to offer the best evidence of this rare condition. The differential diagnosis of HM is broad, including other types of migraine and any condition that can cause transitory neurological signs and symptoms. Neuroimaging, cerebrospinal fluid analysis and electroencephalography are useful, but the diagnosis is clinical with a genetic confirmation. The management relies on the control of triggering factors and even hospitalisation in case of long-lasting auras. As HM is a rare condition, there are no randomised controlled trials, but the evidence for the treatment comes from small studies.

Paroxysmal tonic upgaze: A heterogeneous clinical condition responsive to carbonic anhydrase inhibition

BACKGROUND

Paroxysmal tonic upgaze (PTU), defined as an involuntary upward movement of the eyes, has been considered as a benign phenomenon but may also be associated with ataxia and developmental delay.

METHODS

We report eight children with PTU; six of them also exhibiting symptoms of ataxia and/or developmental delay. Treatment with carbonic anhydrase inhibition was offered to children with persisting and/or severe forms.

RESULTS

Whole-exome sequencing and genome-wide array analysis (n = 7) did not reveal mutations in the three known genes associated with PTU (CACNA1A, GRID2, SEPSECS), whereas by MLPA a heterozygous deletion of exon 31 of the CACNA1A gene could be detected in one patient, her mother and two further family members. Further exome and array analysis showed no recurrent variants in potentially novel PTU-related genes in more than one patient. A de novo variant at a highly conserved position in the SIM1 gene was detected in one patient, for which a pathogenic effect could be speculated. Carbonic anhydrase inhibition was started in five children and proved at least partially effective in all of them.

CONCLUSION

Irrespective of the clinical background and the molecular basic mechanism of PTU, therapeutic carbonic anhydrase inhibition was effective in all five children (acetazolamide, n = 3; sultiame, n = 2) who received this treatment.

CACNA1A Gene Variants in Eight Chinese Patients With a Wide Range of Phenotypes

Background: The CACNA1A gene encodes the voltage-dependent P/Q-type calcium channel subunit alpha-1A, which is widely expressed throughout the CNS. The biological roles of the P/Q channel are diverse and the phenotypic spectrum caused by CACNA1A mutations is wide. The aim of this study is to demonstrate its phenotypic diversity and analyze the genotype-phenotype correlations in a cohort of Chinese patients. Methods: Patients with hemiplegic migraine, cerebellar ataxia, developmental delay, or epilepsy without known causes were tested by trios whole-exome sequencing. Patients with pathogenic CACNA1A gene variants were recruited. The clinical information of the patients was collected, and the association between the genotype and the phenotype was investigated. Results: In total, eight patients (six females and two males) were found to have CACNA1A gene variants. All the variants were de novo including six missense variants and one frameshift variant. Four de novo missense variants were found in five patients located in the S4, S5, or S6 transmembrane segments of Domain II and III (p.R1352Q, p.G701V, p.A713T, p.V1393M). All of them were correlated with severe phenotypes, including three with sporadic hemiplegic migraine type 1 and epilepsy, and two with developmental and epileptic encephalopathy. The other two missense variants, p.Y62C and p.F1814L, located in the cytoplasmic side of the N-terminus and C-terminus, respectively. The variant p.Y62C was associated with severe hemiconvulsion-hemiplegia-epilepsy syndrome, and p.F1814L was associated with relatively mild phenotypes. All the missense variants were speculated as gain-of-function (GOF) mutations. The only frameshift variant, p.Q681Rfs^*100, a lose-of-function (LOF) mutation, was found in a patient with episodic ataxia type 2. Meanwhile, all the patients had developmental delay ranging from mild to severe, as well as cerebellar ataxia including one with congenital ataxia, one with episodic ataxia, and six with non-progressive ataxia. Conclusions: CACNA1A variants could lead to a wide spectrum of neurological disorders including epileptic or non-epileptic paroxysmal events, cerebellar ataxia, and developmental delay. The variants could be both GOF and LOF mutations. There appeared to be some correlations between genotypes and phenotypes.

The neuropsychiatric phenotype in CACNA1A mutations: a retrospective single center study and review of the literature

BACKGROUND AND PURPOSE

CACNA1A encodes the α1 subunit of the neuronal calcium channel P/Q. CACNA1A mutations underlie three allelic disorders: familial hemiplegic migraine type 1 (FHM1), episodic ataxia type 2 (EA2) and spinocerebellar ataxia type 6 (SCA6). A clear-cut genotype-phenotype correlation is often lacking since clinical manifestations may overlap. Several case reports have described cognitive and behavioral features in CACNA1A disorders, but studies in larger case series are lacking.

METHODS

Genetically confirmed CACNA1A cases were retrieved from the database of the ataxia outpatient clinic of the Department of Neurology at Innsbruck Medical University. Clinical charts and neuropsychological test results were retrospectively analyzed. In addition, a review of the literature including only genetically confirmed cases was performed.

RESULTS

Forty-four CACNA1A cases were identified in our database. Delayed psychomotor milestones and poor school performance were described in seven (four FHM1, three EA2) and eight (three FHM1, five EA2) patients, respectively. Psychiatric comorbidities were diagnosed in eight patients (two FHM1, six EA2). Neuropsychological testing was available for 23 patients (11 FHM1, 10 EA2, two SCA6). Various cognitive deficits were documented in 21 cases (all patients except one SCA6). Impairments were predominantly seen in figural memory, visuoconstructive abilities and verbal fluency. In the literature, an early psychomotor delay is described in several children with EA2 and FHM1, whilst reports of cognitive and psychiatric findings from adult cases are scarce.

CONCLUSIONS

Neuropsychiatric manifestations are common in episodic CACNA1A disorders. In the case of otherwise unexplained developmental delay and a positive family history, CACNA1A mutations should be considered in the differential diagnosis.

Genomic analysis identifies masqueraders of full-term cerebral palsy

Objective

Cerebral palsy is a common, heterogeneous neurodevelopmental disorder that causes movement and postural disabilities. Recent studies have suggested genetic diseases can be misdiagnosed as cerebral palsy. We hypothesized that two simple criteria, that is, full-term births and nonspecific brain MRI findings, are keys to extracting masqueraders among cerebral palsy cases due to the following: (1) preterm infants are susceptible to multiple environmental factors and therefore demonstrate an increased risk of cerebral palsy and (2) brain MRI assessment is essential for excluding environmental causes and other particular disorders.

Methods

A total of 107 patients-all full-term births-without specific findings on brain MRI were identified among 897 patients diagnosed with cerebral palsy who were followed at our center. DNA samples were available for 17 of the 107 cases for trio whole-exome sequencing and array comparative genomic hybridization. We prioritized variants in genes known to be relevant in neurodevelopmental diseases and evaluated their pathogenicity according to the American College of Medical Genetics guidelines.

Results

Pathogenic/likely pathogenic candidate variants were identified in 9 of 17 cases (52.9%) within eight genes: CTNNB1,CYP2U1,SPAST,GNAO1,CACNA1A,AMPD2,STXBP1, and SCN2A. Five identified variants had previously been reported. No pathogenic copy number variations were identified. The AMPD2 missense variant and the splice-site variants in CTNNB1 and AMPD2 were validated by in vitro functional experiments.

Interpretation

The high rate of detecting causative genetic variants (52.9%) suggests that patients diagnosed with cerebral palsy in full-term births without specific MRI findings may include genetic diseases masquerading as cerebral palsy.

Stroke-Like Episodes and Cerebellar Syndrome in Phosphomannomutase Deficiency (PMM2-CDG): Evidence for Hypoglycosylation-Driven Channelopathy

Stroke-like episodes (SLE) occur in phosphomannomutase deficiency (PMM2-CDG), and may complicate the course of channelopathies related to Familial Hemiplegic Migraine (FHM) caused by mutations in CACNA1A (encoding Ca_V2.1 channel). The underlying pathomechanisms are unknown. We analyze clinical variables to detect risk factors for SLE in a series of 43 PMM2-CDG patients. We explore the hypothesis of abnormal Ca_V2.1 function due to aberrant N-glycosylation as a potential novel pathomechanism of SLE and ataxia in PMM2-CDG by using whole-cell patch-clamp, N-glycosylation blockade and mutagenesis. Nine SLE were identified. Neuroimages showed no signs of stroke. Comparison of characteristics between SLE positive versus negative patients' group showed no differences. Acute and chronic phenotypes of patients with PMM2-CDG or CACNA1A channelopathies show similarities. Hypoglycosylation of both Ca_V2.1 subunits (α_1A and α_2α) induced gain-of-function effects on channel gating that mirrored those reported for pathogenic CACNA1A mutations linked to FHM and ataxia. Unoccupied N-glycosylation site N283 at α_1A contributes to a gain-of-function by lessening Ca_V2.1 inactivation. Hypoglycosylation of the α₂δ subunit also participates in the gain-of-function effect by promoting voltage-dependent opening of the Ca_V2.1 channel. Ca_V2.1 hypoglycosylation may cause ataxia and SLEs in PMM2-CDG patients. Aberrant Ca_V2.1 N-glycosylation as a novel pathomechanism in PMM2-CDG opens new therapeutic possibilities.

Biotin and Acetazolamide for Treatment of an Unusual Child With Autism Plus Lack of Nail and Hair Growth

BACKGROUND

Patients with autism spectrum disorder and developmental delay or encephalopathy rarely demonstrate no or negligible hair and nail growth, suggesting a biotin-responsive clinical disorder.

METHODS

A ten-year-old girl presented with features of autism spectrum disorder, isolated headaches, and episodes of headaches and limb shaking. Her medical history revealed that her hair and nails did not grow. Administration of biotin restored her nail and hair growth and improved intellectual ability and school performance. Her episodes of headaches, single limb shaking, and loss of consciousness responded to administration of acetazolamide, and her school performance and social skills further improved.

RESULTS

A de novo c.1091 C > T, p.T364M pathogenic variant was found in the ATP1A2 gene by whole-exome sequencing, but a genetic etiology in the biotin-responsive metabolic pathways was not identified.

CONCLUSIONS

The combination of biotin and acetazolamide treatment was successful in restoring normal mental function and school performance. Poor or no clinical nail and hair growth in any child with a developmental delay-autism spectrum disorder presentation should be considered as evidence for a biotin-responsive genetic disorder even when exome testing is negative.

Spinocerebellar [corrected] Ataxia Type 6: Molecular Mechanisms and Calcium Channel Genetics

Spinocerebellar ataxia (SCA) type 6 is an autosomal dominant disease affecting cerebellar degeneration. Clinically, it is characterized by pure cerebellar dysfunction, slowly progressive unsteadiness of gait and stance, slurred speech, and abnormal eye movements with late onset. Pathological findings of SCA6 include a diffuse loss of Purkinje cells, predominantly in the cerebellar vermis. Genetically, SCA6 is caused by expansion of a trinucleotide CAG repeat in the last exon of longest isoform CACNA1A gene on chromosome 19p13.1-p13.2. Normal alleles have 4-18 repeats, while alleles causing disease contain 19-33 repeats. Due to presence of a novel internal ribosomal entry site (IRES) with the mRNA, CACNA1A encodes two structurally unrelated proteins with distinct functions within an overlapping open reading frame (ORF) of the same mRNA: (1) α1A subunit of P/Q-type voltage gated calcium channel; (2) α1ACT, a newly recognized transcription factor, with polyglutamine repeat at C-terminal end. Understanding the function of α1ACT in physiological and pathological conditions may elucidate the pathogenesis of SCA6. More importantly, the IRES, as the translational control element of α1ACT, provides a potential therapeutic target for the treatment of SCA6.

Clinically severe CACNA1A alleles affect synaptic function and neurodegeneration differentially

Dominant mutations in CACNA1A, encoding the α-1A subunit of the neuronal P/Q type voltage-dependent Ca2+ channel, can cause diverse neurological phenotypes. Rare cases of markedly severe early onset developmental delay and congenital ataxia can be due to de novo CACNA1A missense alleles, with variants affecting the S4 transmembrane segments of the channel, some of which are reported to be loss-of-function. Exome sequencing in five individuals with severe early onset ataxia identified one novel variant (p.R1673P), in a girl with global developmental delay and progressive cerebellar atrophy, and a recurrent, de novo p.R1664Q variant, in four individuals with global developmental delay, hypotonia, and ophthalmologic abnormalities. Given the severity of these phenotypes we explored their functional impact in Drosophila. We previously generated null and partial loss-of-function alleles of cac, the homolog of CACNA1A in Drosophila. Here, we created transgenic wild type and mutant genomic rescue constructs with the two noted conserved point mutations. The p.R1673P mutant failed to rescue cac lethality, displayed a gain-of-function phenotype in electroretinograms (ERG) recorded from mutant clones, and evolved a neurodegenerative phenotype in aging flies, based on ERGs and transmission electron microscopy. In contrast, the p.R1664Q variant exhibited loss of function and failed to develop a neurodegenerative phenotype. Hence, the novel R1673P allele produces neurodegenerative phenotypes in flies and human, likely due to a toxic gain of function.

Missense mutations of CACNA1A are a frequent cause of autosomal dominant nonprogressive congenital ataxia

BACKGROUND

Mutations in the CACNA1A gene, encoding the pore-forming CaV2.1 (P/Q-type) channel α1A subunit, localized at presynaptic terminals of brain and cerebellar neurons, result in clinically variable neurological disorders including hemiplegic migraine (HM) and episodic or progressive adult-onset ataxia (EA2, SCA6). Most recently, CACNA1A mutations have been identified in patients with nonprogressive congenital ataxia (NPCA).

METHODS

We performed targeted resequencing of known genes involved in cerebellar dysfunction, in 48 patients with congenital or early onset ataxia associated with cerebellar and/or vermis atrophy.

RESULTS

De novo missense mutations of CACNA1A were found in four patients (4/48, ∼8.3%). Three of them developed migraine before or after the onset of ataxia. Seizures were present in half of the cases.

CONCLUSION

Our results expand the clinical and mutational spectrum of CACNA1A-related phenotype in childhood and suggest that CACNA1A screening should be implemented in this subgroup of ataxias.

Combined early treatment in hemiplegic attacks related to CACNA1A encephalopathy with brain oedema: Blocking the cascade?

Introduction Variants in the CACNA1A gene on chromosome 19p13 result in a spectrum of neurological phenotypes ranging from familial or sporadic hemiplegic migraine to congenital or progressive encephalopathies. Patients with CACNA1A variants often show acute attacks with ataxia or hemiplegia till coma, sometimes related to unilateral brain oedema. No guidelines for the medical management of these attacks are available since treatment is empiric, and many cases do not respond to common antimigraine drugs. Case description We report on the emergency personalized treatment protocol used in an 11 year-old girl with CACNA1A-related encephalopathy for the management of acute attacks of headache, hemiconvulsions and hemiplegia with coma. Discussion Combined corticosteroid pulses and hypertonic solution led to a reduction in severity and duration of acute attacks when administered in the early stages, characterized by migraine, seizure, fever, vomiting and impairment of consciousness associated to hemispheric slowing on the EEG.

A Single Amino Acid Deletion (ΔF1502) in the S6 Segment of CaV2.1 Domain III Associated with Congenital Ataxia Increases Channel Activity and Promotes Ca2+ Influx

Mutations in the CACNA1A gene, encoding the pore-forming Ca_V2.1 (P/Q-type) channel α_1A subunit, result in heterogeneous human neurological disorders, including familial and sporadic hemiplegic migraine along with episodic and progressive forms of ataxia. Hemiplegic Migraine (HM) mutations induce gain-of-channel function, mainly by shifting channel activation to lower voltages, whereas ataxia mutations mostly produce loss-of-channel function. However, some HM-linked gain-of-function mutations are also associated to congenital ataxia and/or cerebellar atrophy, including the deletion of a highly conserved phenylalanine located at the S6 pore region of α_1A domain III (ΔF1502). Functional studies of ΔF1502 Ca_V2.1 channels, expressed in Xenopus oocytes, using the non-physiological Ba²⁺ as the charge carrier have only revealed discrete alterations in channel function of unclear pathophysiological relevance. Here, we report a second case of congenital ataxia linked to the ΔF1502 α_1A mutation, detected by whole-exome sequencing, and analyze its functional consequences on Ca_V2.1 human channels heterologously expressed in mammalian tsA-201 HEK cells, using the physiological permeant ion Ca²⁺. ΔF1502 strongly decreases the voltage threshold for channel activation (by ~ 21 mV), allowing significantly higher Ca²⁺ current densities in a range of depolarized voltages with physiological relevance in neurons, even though maximal Ca²⁺ current density through ΔF1502 Ca_V2.1 channels is 60% lower than through wild-type channels. ΔF1502 accelerates activation kinetics and slows deactivation kinetics of Ca_V2.1 within a wide range of voltage depolarization. ΔF1502 also slowed Ca_V2.1 inactivation kinetic and shifted the inactivation curve to hyperpolarized potentials (by ~ 28 mV). ΔF1502 effects on Ca_V2.1 activation and deactivation properties seem to be of high physiological relevance. Thus, ΔF1502 strongly promotes Ca²⁺ influx in response to either single or trains of action potential-like waveforms of different durations. Our observations support a causative role of gain-of-function Ca_V2.1 mutations in congenital ataxia, a neurodevelopmental disorder at the severe-most end of CACNA1A-associated phenotypic spectrum.

Genetic Evidence for Possible Involvement of the Calcium Channel Gene CACNA1A in Autism Pathogenesis in Chinese Han Population

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders. Recent studies suggested that calcium channel genes might be involved in the genetic etiology of ASD. CACNA1A, encoding an alpha-1 subunit of voltage-gated calcium channel, has been reported to play an important role in neural development. Previous study detected that a single nucleotide polymorphism (SNP) in CACNA1A confers risk to ASD in Central European population. However, the genetic relationship between autism and CACNA1A in Chinese Han population remains unclear. To explore the association of CACNA1A with autism, we performed a family-based association study. First, we carried out a family-based association test between twelve tagged SNPs and autism in 239 trios. To further confirm the association, the sample size was expanded to 553 trios by recruiting 314 additional trios. In a total of 553 trios, we identified association of rs7249246 and rs12609735 with autism though this would not survive after Bonferroni correction. Our findings suggest that CACNA1A might play a role in the etiology of autism.

Meta-Analysis of Public Microarray Datasets Reveals Voltage-Gated Calcium Gene Signatures in Clinical Cancer Patients

Voltage-gated calcium channels (VGCCs) are well documented to play roles in cell proliferation, migration, and apoptosis; however, whether VGCCs regulate the onset and progression of cancer is still under investigation. The VGCC family consists of five members, which are L-type, N-type, T-type, R-type and P/Q type. To date, no holistic approach has been used to screen VGCC family genes in different types of cancer. We analyzed the transcript expression of VGCCs in clinical cancer tissue samples by accessing ONCOMINE (www.oncomine.org), a web-based microarray database, to perform a systematic analysis. Every member of the VGCCs was examined across 21 different types of cancer by comparing mRNA expression in cancer to that in normal tissue. A previous study showed that altered expression of mRNA in cancer tissue may play an oncogenic role and promote tumor development; therefore, in the present findings, we focus only on the overexpression of VGCCs in different types of cancer. This bioinformatics analysis revealed that different subtypes of VGCCs (CACNA1C, CACNA1D, CACNA1B, CACNA1G, and CACNA1I) are implicated in the development and progression of diverse types of cancer and show dramatic up-regulation in breast cancer. CACNA1F only showed high expression in testis cancer, whereas CACNA1A, CACNA1C, and CACNA1D were highly expressed in most types of cancer. The current analysis revealed that specific VGCCs likely play essential roles in specific types of cancer. Collectively, we identified several VGCC targets and classified them according to different cancer subtypes for prospective studies on the underlying carcinogenic mechanisms. The present findings suggest that VGCCs are possible targets for prospective investigation in cancer treatment.

Benign paroxysmal torticollis of infancy: An underdiagnosed condition

Benign paroxysmal torticollis is probably an under-diagnosed condition of infancy. It is a self-limiting disorder characterised by periods of unusual, sustained posture of the head and neck, during which the head tilts to one side. Episodes are often accompanied by marked autonomic features, irritability, ataxia, apathy and drowsiness. They last several hours to a few days and are often recurring every few weeks. They subside within the pre-school years; however, during later childhood, there is a tendency to develop migraine. Three cases of benign paroxysmal torticollis are presented and are compared with cases in the literature. A telephone survey has been conducted to determine what is the general awareness of paediatricians of this condition in Cyprus. Eighty-two paediatricians were randomly selected out of 235 paediatricians. All of them agreed to participate. Our cases revealed that benign paroxysmal torticollis may coexist with other problems during infancy. The telephone survey showed that only two out of eighty-two (2.4%) of the paediatricians are aware of the condition, and none of them was confident regarding the management. Our telephone survey clearly shows that Cypriot paediatricians are not familiar with benign paroxysmal torticollis in infancy which is a benign, self-limiting disorder. It is essential to recognise the condition and to reassure parents of its benign course and not to be misdiagnosed for other disorders, such as epileptic seizures. We have shown again that benign paroxysmal torticollis in infancy may coexist with motor delay and hearing problems.

The expanding spectrum of neurological phenotypes in children with ATP1A3 mutations, Alternating Hemiplegia of Childhood, Rapid-onset Dystonia-Parkinsonism, CAPOS and beyond

BACKGROUND

ATP1A3 mutations have now been recognized in infants and children presenting with a diverse group of neurological phenotypes, including Rapid-onset Dystonia-Parkinsonism (RDP), Alternating Hemiplegia of Childhood (AHC), and most recently, Cerebellar ataxia, Areflexia, Pes cavus, Optic atrophy, and Sensorineural hearing loss (CAPOS) syndrome.

METHODS

Existing literature on ATP1A3-related disorders in the pediatric population were reviewed, with attention to clinical features and associated genotypes among those with RDP, AHC, or CAPOS syndrome phenotypes.

RESULTS

While classically defined phenotypes associated with AHC, RDP, and CAPOS syndromes are distinct, common elements among ATP1A3-related neurological disorders include characteristic episodic neurological symptoms and signs that vary in severity, duration, and frequency of occurrence. Affected children typically present in the context of an acute onset of paroxysmal, episodic neurological symptoms ranging from oculomotor abnormalities, hypotonia, paralysis, dystonia, ataxia, seizure-like episodes, or encephalopathy. Neurodevelopmental delays or persistence of dystonia, chorea, or ataxia after resolution of an initial episode are common, providing important clues for diagnosis.

CONCLUSIONS

The phenotypic spectrum of ATP1A3-related neurological disorders continues to expand beyond the distinct yet overlapping phenotypes in patients with AHC, RDP, and CAPOS syndromes. ATP1A3 mutation analysis is appropriate to consider in the diagnostic algorithm for any child presenting with episodic or fluctuating ataxia, weakness or dystonia whether they manifest persistence of neurological symptoms between episodes. Additional work is needed to better identify and classify affected patients and develop targeted treatment approaches.