Alternating hemiplegia of childhood: evolution over time and mouse model corroboration

Phenotype Distinctions in Mice Deficient in the Neuron-Specific α3 Subunit of Na,K-ATPase: Atp1a3tm1Ling/+ and Atp1a3 +/D801Y

ATP1A3 is a Na,K-ATPase gene expressed specifically in neurons in the brain. Human mutations are dominant and produce an unusually wide spectrum of neurological phenotypes, most notably rapid-onset dystonia parkinsonism (RDP) and alternating hemiplegia of childhood (AHC). Here we compared heterozygotes of two mouse lines, a line with little or no expression (Atp1a3tm1Ling/+) and a knock-in expressing p.Asp801Tyr (D801Y, Atp1a3 +/D801Y). Both mouse lines had normal lifespans, but Atp1a3 +/D801Y had mild perinatal mortality contrasting with D801N mice (Atp1a3 +/D801N), which had high mortality. The phenotypes of Atp1a3tm1Ling/+ and Atp1a3 +/D801Y were different, and testing of each strain was tailored to its symptom range. Atp1a3tm1Ling/+ mice displayed little at baseline, but repeated ethanol intoxication produced hyperkinetic motor abnormalities not seen in littermate controls. Atp1a3 +/D801Y mice displayed robust phenotypes: hyperactivity, diminished posture consistent with hypotonia, and deficiencies in beam walk and wire hang tests. Symptoms also included qualitative motor abnormalities that are not well quantified by conventional tests. Paradoxically, Atp1a3 +/D801Y showed sustained better performance than wild type on the accelerating rotarod. Atp1a3 +/D801Y mice were overactive in forced swimming and afterward had intense shivering, transient dystonic postures, and delayed recovery. Remarkably, Atp1a3 +/D801Y mice were refractory to ketamine anesthesia, which elicited hyperactivity and dyskinesia even at higher dose. Neither mouse line exhibited fixed dystonia (typical of RDP patients), spontaneous paroxysmal weakness (typical of AHC patients), or seizures but had consistent, measurable neurological abnormalities. A gradient of variation supports the importance of studying multiple Atp1a3 mutations in animal models to understand the roles of this gene in human disease.

In vitro study of ATP1A3 p.Ala275Pro mutant causing alternating hemiplegia of childhood and rapid-onset dystonia-parkinsonism

Introduction

We previously reported that ATP1A3 c.823G>C (p.Ala275Pro) mutant causes varying phenotypes of alternative hemiplegia of childhood and rapid-onset dystonia-parkinsonism in the same family. This study aims to investigate the function of ATP1A3 c.823G>C (p.Ala275Pro) mutant at the cellular and zebrafish models.

Methods

ATP1A3 wild-type and mutant Hela cell lines were constructed, and ATP1A3 mRNA expression, ATP1A3 protein expression and localization, and Na+-K+-ATPase activity in each group of cells were detected. Additionally, we also constructed zebrafish models with ATP1A3 wild-type overexpression (WT) and p.Ala275Pro mutant overexpression (MUT). Subsequently, we detected the mRNA expression of dopamine signaling pathway-associated genes, Parkinson's disease-associated genes, and apoptosisassociated genes in each group of zebrafish, and observed the growth, development, and movement behavior of zebrafish.

Results

Cells carrying the p.Ala275Pro mutation exhibited lower levels of ATP1A3 mRNA, reduced ATP1A3 protein expression, and decreased Na+-K+-ATPase activity compared to wild-type cells. Immunofluorescence analysis revealed that ATP1A3 was primarily localized in the cytoplasm, but there was no significant difference in ATP1A3 protein localization before and after the mutation. In the zebrafish model, both WT and MUT groups showed lower brain and body length, dopamine neuron fluorescence intensity, escape ability, swimming distance, and average swimming speed compared to the control group. Moreover, overexpression of both wild-type and mutant ATP1A3 led to abnormal mRNA expression of genes associated with the dopamine signaling pathway and Parkinson's disease in zebrafish, and significantly upregulated transcription levels of bad and caspase-3 in the apoptosis signaling pathway, while reducing the transcriptional level of bcl-2 and the bcl-2/bax ratio.

Conclusion

This study reveals that the p.Ala275Pro mutant decreases ATP1A3 protein expression and Na+/K+-ATPase activity. Abnormal expression of either wild-type or mutant ATP1A3 genes impairs growth, development, and movement behavior in zebrafish.

Real life retrospective study of cannabidiol therapy in alternating hemiplegia of childhood

BACKGROUND

Many alternating hemiplegia of childhood (AHC) patients have received Cannabidiol (CBD) but, to our knowledge, there are no published data available.

GOALS

Test the hypothesis that CBD has favorable effects on AHC spells.

METHODS

Retrospective review of available data of AHC patients who received CBD. Primary analysis: Clinical Global Impression Scale of Improvement (CGI-I) score for response of AHC spells to CBD with calculation of 95% confidence interval (CI) for rejection of the null hypothesis. Secondary analyses, performed to achieve an understanding of the effect of CBD as compared to flunarizine, were CGI-I scores of 1) epileptic seizures to CBD, 2) AHC spells to flunarizine, 3) epileptic seizures to flunarizine. Also, Mann-Whitney test was done for comparison of CGI-I scores of CBD and flunarizine to both AHC spells and seizures.

RESULTS

We studied 16 AHC patients seen at Duke University and University of Lyon. CI of CGI-I scores for AHC spells in response to CBD and to flunarizine, each separately, indicated a positive response to each of these two medications: neither overlapped with the null hypothesis score, 4, indicating significant positive responses with p < 0.05 for both. These two scores also did not differ (p = 0.84) suggesting similar efficacy of both: CBD score was 2 ± 1.1 with a 95% CI of 1.5-2.6 and flunarizine score was 2.3 ± 1.3 with a 95% CI of 1.7-3.1. In patients who had seizures, CI calculations indicated a positive effect of CBD on seizure CGI scores but not of flunarizine on seizure scores. CBD was well tolerated with no patients discontinuing it due to side effects and with some reporting positive behavioral changes.

CONCLUSION

Our study indicates a real-life positive effect of CBD on AHC type spells.

Characteristics of non-sleep related apneas in children with alternating hemiplegia of childhood

BACKGROUND

Non-sleep related apnea (NSA) has been observed in alternating hemiplegia of childhood (AHC) but has yet to be characterized.

GOALS

Investigate the following hypotheses: 1) AHC patients manifest NSA that is often severe. 2) NSA is usually triggered by precipitating events. 3) NSA is more likely in patients with ATP1A3 mutations.

METHODS

Retrospective review of 51 consecutive AHC patients (ages 2-45 years) enrolled in our AHC registry. NSAs were classified as mild (not needing intervention), moderate (needing intervention but not perceived as life threatening), or severe (needing intervention and perceived as life threatening).

RESULTS

19/51 patients (37 %) had 52 NSA events (6 mild, 11 moderate, 35 severe). Mean age of onset of NSA (± Standard Error of the Mean (SEM)): 3.8 ± 1.5 (range 0-24) years, frequency during follow up was higher at younger ages as compared to adulthood (year 1: 2.2/year, adulthood: 0.060/year). NSAs were associated with triggering factors, bradycardia and with younger age (p < 0.008 in all) but not with mutation status (p = 0.360). Triggers, observed in 17 patients, most commonly included epileptic seizures in 9 (47 %), anesthesia, AHC spells and intercurrent, stressful, conditions. Management included use of pulse oximeter at home in nine patients, home oxygen in seven, intubation/ventilatory support in seven, and basic CPR in six. An additional patient required tracheostomy. There were no deaths or permanent sequalae.

CONCLUSIONS

AHC patients experience NSAs that are often severe. These events are usually triggered by seizures or other stressful events and can be successfully managed with interventions tailored to the severity of the NSA.

Methodology of a Natural History Study of a Rare Neurodevelopmental Disorder: Alternating Hemiplegia of Childhood as a Prototype Disease

Here, we describe the process of development of the methodology for an international multicenter natural history study of alternating hemiplegia of childhood as a prototype disease for rare neurodevelopmental disorders. We describe a systematic multistep approach in which we first identified the relevant questions about alternating hemiplegia of childhood natural history and expected challenges. Then, based on our experience with alternating hemiplegia of childhood and on pragmatic literature searches, we identified solutions to determine appropriate methods to address these questions. Specifically, these solutions included development and standardization of alternating hemiplegia of childhood-specific spell video-library, spell calendars, adoption of tailored methodologies for prospective measurement of nonparoxysmal and paroxysmal manifestations, unified data collection protocols, centralized data platform, adoption of specialized analysis methods including, among others, Cohen kappa, interclass correlation coefficient, linear mixed effects models, principal component, propensity score, and ambidirectional analyses. Similar approaches can, potentially, benefit in the study of other rare pediatric neurodevelopmental disorders.

Development and testing of methods to record and follow up spells in patients with alternating hemiplegia of childhood

BACKGROUND

Developing methods to record Alternating Hemiplegia of Childhood (AHC) spells is essential for clinical trials and patient care.

OBJECTIVES

Test the following hypotheses: 1) Video-library training improves participants' ability to correctly identify AHC spells. 2) A custom-designed event-calendar with weekly reviews results in consistent documentation of such events over time. 3) Use of an electronic diary (e-Diary) to register events is a useful tool.

METHODS

1) A video-library of AHC type spells was developed along with specific training; the effect of the training was tested in 36 caregivers. 2) An event-calendar was similarly developed and provided to 5 caregivers with weekly videoconference meetings for 8 weeks. 3) An e-Diary was developed and offered to 33 patients; time of usage and caregivers' feedback (telephone interview) were analyzed.

RESULTS

1) Video-library training: Wilcoxon test showed improvement in caregiver identification of spells (p = 0.047), Cohen's Kappa demonstrated high degree of agreement between caregivers'-experts' classifications (>0.9). 2) Event-calendar: 96.42% of entries had complete information; this did not change during follow up (p = 0.804). 3) e-Diary: whereas 52% of respondents used the e-Diary when offered (duration: 10.5 ± 8.1 months), 96.3% indicated they would use it in future studies. Those who used it for 13 months, were very likely to use it during the rest of that year.

CONCLUSIONS

Video-library training improved spell identification. Calendar with weekly reviews resulted in a sustained and consistent record keeping. Caregivers' e-Diary feedback was encouraging with long-term usage in many. These approaches could be helpful for AHC and, potentially, in similar disorders.

Characterization of sedation and anesthesia complications in patients with alternating hemiplegia of childhood

BACKGROUND

Alternating hemiplegia of childhood (AHC) pathophysiology suggests predisposition to sedation and anesthesia complications.

GOALS

Hypotheses: 1) AHC patients experience high rates of sedation-anesthesia complications. 2) ATP1A3 mutation genotype positivity, age, and AHC severity correlate with more severe complications. 3) Prior short QTc correlates with cardiac rhythm complications.

METHODS

Analysis of 34 consecutive AHC patients who underwent sedation or anesthesia. Classification of complications: mild (not requiring intervention), moderate (intervention), severe (intervention, risk for permanent injury or potential life-threatening emergency).

STATISTICS

Fisher Exact test, Spearman correlations.

RESULTS

These patients underwent 129 procedures (3.79 ± 2.75 procedures/patient). Twelve (35%) experienced complications during at least one procedure. Fourteen/129 procedures (11%) manifested one or more complications (2.3% mild, 7% moderate, 1.6% severe). Of the total 20 observed complications, six (33.3%) were severe: apneas (2), seizures (2), bradycardia (1), ventricular fibrillation that responded to resuscitation (1). Moderate complications: non-life-threatening bradycardias, apneas, AHC spells or seizures. Complications occurred during sedation or anesthesia and during procedures or recovery periods. Patients with disease-associated ATP1A3 variants were more likely to have moderate or severe complications. There was no correlation between complications and age or AHC severity. Presence of prior short QTc correlated with cardiac rhythm complications. After this series was analyzed, another patient had severe recurrent laryngeal dystonia requiring tracheostomy following anesthesia with intubation.

CONCLUSIONS

During sedation or anesthesia, AHC patients, particularly those with ATP1A3 variants and prior short QTc, are at risk for complications consistent with AHC pathophysiology. Increased awareness is warranted during planning, performance, and recovery from such procedures.

Non‐Stationary Outcome of Alternating Hemiplegia of Childhood into Adulthood

Background

Objectives

Methods

Results

Conclusions

Genetically altered animal models for ATP1A3-related disorders

Within the past 20 years, particularly with the advent of exome sequencing technologies, autosomal dominant and de novo mutations in the gene encoding the neurone-specific α3 subunit of the Na+,K+-ATPase (NKA α3) pump, ATP1A3, have been identified as the cause of a phenotypic continuum of rare neurological disorders. These allelic disorders of ATP1A3 include (in approximate order of severity/disability and onset in childhood development): polymicrogyria; alternating hemiplegia of childhood; cerebellar ataxia, areflexia, pes cavus, optic atrophy and sensorineural hearing loss syndrome; relapsing encephalopathy with cerebellar ataxia; and rapid-onset dystonia-parkinsonism. Some patients present intermediate, atypical or combined phenotypes. As these disorders are currently difficult to treat, there is an unmet need for more effective therapies. The molecular mechanisms through which mutations in ATP1A3 result in a broad range of neurological symptoms are poorly understood. However, in vivo comparative studies using genetically altered model organisms can provide insight into the biological consequences of the disease-causing mutations in NKA α3. Herein, we review the existing mouse, zebrafish, Drosophila and Caenorhabditis elegans models used to study ATP1A3-related disorders, and discuss their potential contribution towards the understanding of disease mechanisms and development of novel therapeutics.