The treatment and management of alternating hemiplegia of childhood

Precision therapy for a medically actionable ATP1A3 variant from a genomic medicine program in an underserved population

BACKGROUND

Genomic medicine is revolutionizing the diagnosis of rare diseases, but the implementation has not benefited underrepresented populations to the same degree. Here, we report the case of a 7-year-old boy with hypotonia, global developmental delay, strabismus, seizures, and previously suspected mitochondrial myopathy. This proband comes from an underrepresented minority and was denied exome sequencing by his public insurance.

METHODS

After informed consent was obtained, buccal cells from the proband were collected and whole exome sequencing was performed. Illumina Dragen and Emedgene software was used to analyze the data at Baylor Genetics. The variants were further intepreted according to ACMG guidelines and the patient's phenotype.

RESULTS

Through whole-exome sequencing (WES) under the Community Texome project, he was found to have a heterozygous de novo pathogenic variant in the ATP1A3 gene located on chromosome 19q13.

CONCLUSION

In retrospect, his symptomatology matches the known medical conditions associated with the ATP1A3 gene namely Alternating Hemiplegia of Childhood 2 (AHC), a rare autosomal dominant disorder with an incidence of 1 in one million. His single nucleotide variant, (c.2401G>A, p.D801N), is predicted to be damaging. The specific amino acid change p.D801N has been previously reported in ClinVar along with the allelic variant p.D801Y and both are considered pathogenic. The identification of this variant altered medical management for this patient as he was started on a calcium antagonist and has reported no further hemiplegic episodes. This case illustrates the value of implementing genomic medicine for precision therapy in underserved populations.

Alternating hemiplegia of childhood

Alternating hemiplegia of childhood (AHC) is characterized by recurrent episodes of hemiplegia which may alternate sides between attacks. The condition is associated with severe neurodevelopmental disorder presenting in early infancy, and may encompass a wide range of other paroxysmal manifestations (e.g., dystonia, nystagmus, dysautonomia) and pervasive neurological disabilities (e.g., developmental delay, learning disabilities, choreoathetosis, and ataxia). Epileptic seizures are particularly common among patients with AHC. Diagnosis is usually based on history and clinical grounds using the Aicardi criteria. Mutations in the ATP1A3 gene are implicated in the disease pathology of the condition, as well as several other neurodevelopmental disorders, suggesting AHC forms part of a spectrum of overlapping clinical syndromes rather than a distinct clinical entity per se. Management of patients with AHC includes the rapid induction of sleep during paroxysmal attacks and the avoidance of identified triggers. Pharmacotherapeutic treatments have a role in managing epileptic seizures, as well as in the prevention of paroxysmal attacks wherein flunarizine remains the treatment of choice.

Alternating hemiplegia of childhood: a distinct clinical entity and ATP1A3-related disorders: A narrative review

Alternating Hemiplegia of Childhood (AHC) is a rare disorder with onset in the first 18 months of life characterized by stereotyped paroxysmal manifestations of tonic and dystonic attacks, nystagmus with other oculomotor abnormalities, respiratory and autonomic dysfunctions. AHC is often associated with epileptic seizures and developmental delay. Hemiplegic paroxysm is the most remarkable symptom, although AHC includes a large series of clinical manifestations that interfere with the disease course. No cure is available and the treatment involves many specialists and therapies. Flunarizine is the most commonly used drug for reducing the frequency and intensity of paroxysmal events. Mutations in ATP1A2, particularly in ATP1A3, are the main genes responsible for AHC. Some disorders caused by ATP1A3 variants have been defined as ATP1A3-related disorders, including rapid-onset dystonia-parkinsonism, cerebellar ataxia, pes cavus, optic atrophy, sensorineural hearing loss, early infant epileptic encephalopathy, child rapid-onset ataxia, and relapsing encephalopathy with cerebellar ataxia. Recently, the term ATP1A3 syndrome has been identified as a fever-induced paroxysmal weakness and encephalopathy, slowly progressive cerebellar ataxia, childhood-onset schizophrenia/autistic spectrum disorder, paroxysmal dyskinesia, cerebral palsy/spastic paraparesis, dystonia, dysmorphism, encephalopathy, MRI abnormalities without hemiplegia, and congenital hydrocephalus. Herewith, we discussed about historical annotations of AHC, symptoms, signs and associated morbidities, diagnosis and differential diagnosis, treatment, prognosis, and genetics. We also reported on the ATP1A3-related disorders and ATP1A3 syndrome, as 2 recently established and expanded genetic clinical entities.

Alternating Hemiplegia of Childhood: neurological comorbidities and intrafamilial variability

BACKGROUND

Alternating of Childhood (AHC) is an uncommon and complex disorder characterized by age of onset before 18 months with recurrent hemiplegia of one or either sides of the body or quadriplegia. The disorder is mainly caused by mutations in ATP1A3 gene, and to a lesser extent in ATP1A2 gene. In AHC neurological co-morbidities are various and frequently reported including developmental delay, epilepsy, tonic or dystonic spells, nystagmus,autonomic manifestations with intrafamilial variability.

CASE PRESENTATION

Clinical and genetic findings of a couple of twins (Family 1: Case 1 and Case 2) and a couple of siblings (Family 2: Case 3 and Case 4) coming from two different Italian families affected by AHC were deeply examined. In twins of Family 1, a pathogenic variant in ATP1A3 gene (c.2318A>G) was detected. In siblings of Family 2, the younger brother showed a novel GRIN2A variant (c.3175 T > A), while the older carried the same GRIN2A variant, and two missense mutations in SCNIB (c.632 > A) and KCNQ2 (1870 G > A) genes. Clinical manifestations of the four affected children were reported along with cases of AHC drawn from the literature.

CONCLUSIONS

Hemiplegic episode is only a sign even if the most remarkable of several and various neurological comorbidities in AHC affected individuals. Molecular analysis of the families here reported showed that clinical features of AHC may be also the result of an unexpected genetic heterogeneity.

Alternating Hemiplegia of Childhood in a Child Harboring a Novel TBC1D24 Mutation: Case Report and Literature Review

Alternating Hemiplegia of Childhood (AHC) is a rare neurological disease characterized by early-onset recurrent paroxysmal events and persistent neurological deficits. TBC1D24 gene variants have been associated with a phenotypic spectrum having epilepsy as the main clinical manifestation. Herein, we report the case of a child affected by developmental delay, polymorphic seizures, and nonepileptic episodes characterized by hemiplegia or bilateral plegia, pallor, hypotonia, and dystonic postures without loss of consciousness that resolved with sleep. Noteworthy, the patient fulfills all the diagnostic criteria for AHC. An epilepsy gene panel revealed a novel TBC1D24 mutation. This variant may be considered a PM5, according to the American College of Medical Genetics and Genomics guidelines. TBC1D24 gene variants are associated with various clinical features, and increasing data confirms the association with permanent and paroxysmal movement disorders. Our report suggests that the TBC1D24 molecular analysis could be considered in the diagnostic workup of AHC patients.

Alternating hemiplegia of childhood: An electroclinical study of sleep and hemiplegia

OBJECTIVE

Alternating Hemiplegia of Childhood (AHC) is characterised by paroxysmal hemiplegic episodes and seizures. Remission of hemiplegia upon sleep is a clinical diagnostic feature of AHC. We investigated whether: 1) Hemiplegic events are associated with spectral EEG changes 2) Sleep in AHC is associated with clinical or EEG spectral features that may explain its restorative effect.

METHODS

We retrospectively performed EEG spectral analysis in five adults with AHC and twelve age-/gender-matched epilepsy controls. Five-minute epochs of hemiplegic episodes and ten-minute epochs of four sleep stages were selected from video-EEGs. Arousals were counted per hour of sleep.

RESULTS

We found 1) hemispheric differences in pre-ictal and ictal spectral power (p = 0.034), during AHC hemiplegic episodes 2) 22% reduced beta power (p = 0.017) and 26% increased delta power (p = 0.025) during wakefulness in AHC versus controls. There were 98% more arousals in the AHC group versus controls (p = 0.0003).

CONCLUSIONS

There are hemispheric differences in spectral power preceding hemiplegic episodes in adults with AHC, and sleep is disrupted.

SIGNIFICANCE

Spectral EEG changes may be a potential predictive tool for AHC hemiplegic episodes. Significantly disrupted sleep is a feature of AHC.

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.

Alternating Hemiplegia of Childhood: A Series of Genetically Confirmed Four Cases from Southern India with Review of Published Literature

Alternating hemiplegia of childhood (AHC) is a rare autosomal dominant neurodevelopmental disorder with mutation on ATP1A3 gene. Delay in diagnosis and inappropriate diagnosis are common. In this article, we described four genetically confirmed AHC patients to provide an improved understanding of the disorder. First symptom in two patients was seizures and in other two patients was abnormal eye deviation. All had onset of plegic attacks within the first 18 months of their life. Tone abnormalities and movement disorders were present in all patients. Electroencephalogram was abnormal in two patients and all had normal magnetic resonance imaging of the brain. Response to treatment of plegic attacks was poor and also epilepsy was drug resistant. All cases had significant development delay and disability as of last follow-up. Although there is no effective treatment so far, early diagnosis is required to avoid unnecessary treatment.

ATP1A3-Related Disorders: An Ever-Expanding Clinical Spectrum

The Na+/K+ ATPases are Sodium-Potassium exchanging pumps, with a heteromeric α-β-γ protein complex. The α3 isoform is required as a rescue pump, after repeated action potentials, with a distribution predominantly in neurons of the central nervous system. This isoform is encoded by the ATP1A3 gene. Pathogenic variants in this gene have been implicated in several phenotypes in the last decades. Carriers of pathogenic variants in this gene manifest neurological and non-neurological features in many combinations, usually with an acute onset and paroxysmal episodes triggered by fever or other factors. The first three syndromes described were: (1) rapid-onset dystonia parkinsonism; (2) alternating hemiplegia of childhood; and, (3) cerebellar ataxia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS syndrome). Since their original description, an expanding number of cases presenting with atypical and overlapping features have been reported. Because of this, ATP1A3-disorders are now beginning to be viewed as a phenotypic continuum representing discrete expressions along a broadly heterogeneous clinical spectrum.

Gross Motor Function Disorders in Patients with Alternating Hemiplegia of Childhood

Background

Alternating hemiplegia of Childhood (AHC) is a rare disease manifested by transient episodes of hemiplegia and other neurological disorders. Delayed motor development has been reported in patients with AHC, but detailed features of the motor impairment have not been described so far.

Aim

The aim of the study was to evaluate gross motor function between attacks in a group of Polish patients with AHC.

Materials and methods

The interictal gross motor function was assessed using the Gross Motor Function AHC scale, which consisted of 41 motor tasks. The study group consisted of 10 patients with AHC older than 2 years of age. The control group consisted of 30 age- and gender-matched subjects. The results achieved in each of the 41 tasks by the study subjects were compared to the results obtained with controls using the non-parametric Mann-Whitney U-test. In tasks 38-41, mean times were compared between the study subjects and controls.

Results

The study revealed gross motor function impairment in patients with AHC. The greatest differences compared to controls concerned such skills as standing on toes, walking on toes, walking on heels, as well as running and hopping on one leg and on alternate legs. Significant impairment of the motor function of the upper limbs was also found.

Conclusions

The study confirmed motor function impairment between attacks in patients with AHC. The study findings may indicate the need to introduce individualised physiotherapy management of patients with AHC.

Social impairments in alternating hemiplegia of childhood

AIM

To evaluate presence and severity of social impairments in alternating hemiplegia of childhood (AHC) and determine factors that are associated with social impairments.

METHOD

This was a retrospective analysis of 34 consecutive patients with AHC (19 females, 15 males; mean age: 9y 7mo, SD 8y 2mo, range 2y 7mo-40y), evaluated with the Social Responsiveness Scale, Second Edition (SRS-2).

RESULTS

SRS-2 scores, indicating level of social impairment, were higher than population means (75, SD 14 vs 50, SD 10, p<0.001). Of these, 27 out of 34 had high scores: 23 severe (>76), four moderate (66-76). All subscale domains, including social cognition, social communication, social awareness, social motivation, restricted interests, and repetitive behavior, had abnormal scores compared to population means (p<0.001). High SRS-2 scores were associated with the presence of autism spectrum disorder (ASD) and epilepsy (p=0.01, p=0.04), but not with other scales of AHC disease symptomatology. All nine patients who received formal evaluations for ASD, because they had high SRS-2 scores, were diagnosed with ASD.

INTERPRETATION

Most patients with AHC have impaired social skills involving multiple domains. ASD is not uncommon. High SRS-2 scores in patients with AHC support referral to ASD evaluation. Our findings are consistent with current understandings of the pathophysiology of AHC and ASD, both thought to involve GABAergic dysfunction.

WHAT THIS PAPER ADDS

Most patients with alternating hemiplegia of childhood (AHC) have impaired social skills involving multiple domains. These impairments are significant compared to population means. Most patients with AHC have high Social Responsiveness Scale, Second Edition (SRS-2) scores. Patients with AHC with high SRS-2 scores are likely to have autism spectrum disorder.

Mutational and phenotypic expansion of ATP1A3-related disorders: Report of nine cases

BACKGROUND

Mutations in the ATP1A3 gene are known to be the cause of three distinct neurological syndromes including alternating hemiplegia of childhood (AHC), rapid-onset dystonia parkinsonism (RDP) and cerebellar ataxia, arefexia, pes cavus, optic atrophy and sensorineural hearing impairment (CAPOS). Recent studies have suggested the broader diversity of ATP1A3-related disorders. This study aimed to investigate the clinical spectrum in patients carrying causative mutations within the ATP1A3 gene.

METHOD

The medical histories of nine unrelated patients with diverse phenotypes harboring variants in ATP1A3 were retrospectively analyzed after they were referred to a tertiary epilepsy center in one of the two different health care systems (Germany or Thailand). Clinical features, neurophysiological data, imaging results, genetic characteristics and treatments were reviewed.

RESULTS

Three patients harbor novel mutations in the ATP1A3 gene. Atypical clinical features and imaging findings were observed in two cases, one with hemiplegia-hemiconvulsion-epilepsy syndrome, and the other with neurodegeneration with brain iron accumulation. All nine patients presented with intellectual impairment. Alternating hemiplegia of childhood (AHC) was the most common phenotype (67%). Flunarizine and topiramate led to symptom reduction in 83% and 25% of AHC cases administered, respectively.

CONCLUSION

The present case series expands the clinical and genetic spectrum of ATP1A3-related disorders.

Management of Alternating Hemiplegia of Childhood: A Review

Alternating hemiplegia of childhood is a severe neurological disorder with infantile-onset recurrent episodes of hemiplegia on either side of the body and other paroxysmal events such as seizures, dystonia, tonic episodes, abnormal eye movements or autonomic dysfunction, primarily due to de novo pathogenic mutations in the ATP1A3 gene. The burden of neuromorbidities is significant and includes epilepsy; attention-deficit/hyperactivity disorder; behavioral difficulties; motor, cognitive, adaptive, and learning impairment; ataxia; movement disorders; and migraine. Comprehensive multispecialty clinic with the availability of various specialists with considerable experience in alternating hemiplegia of childhood is beneficial. A comprehensive treatment plan including strict maintenance of a diary about different paroxysmal events is helpful. Disease-modifying therapy of alternating hemiplegia of childhood does not exist, and several agents such as benzodiazepines, flunarizine, topiramate, ketogenic diet, triheptanoin, steroid, amantadine, memantine, aripiprazole, oral ATP, coenzyme Q, acetazolamide, dextromethorphan, and vagus nerve stimulator have been tried with various rates of success by aborting attacks or reducing the frequency or severity of paroxysmal spells. The apparent efficacy of flunarizine is based on its use in hundreds of patients, albeit in open-label experience, but most of the other agents' reports of efficacy were from single case reports or case series of only a handful of patients. Besides reviewing existing data about individual agent active against paroxysmal events, we also review the management principles for coexisting neurological issues. However, with rapid advancement in the understanding of molecular pathogenesis and network abnormality of this disease, the treatment paradigm of alternating hemiplegia of childhood may significantly alter over the next decade.

Physical Therapy for a Patient With Alternating Hemiplegia of Childhood: A Case Report

PURPOSE

Alternating hemiplegia of childhood (AHC) is a rare neurological disorder that can influence posture and movement during critical periods of motor development. There are no descriptions of physical therapy for children with AHC. The purpose of this case report is to present an example of physical therapy evaluation, intervention, and outcomes for a child with AHC.

SUMMARY OF KEY POINTS

Physical therapy services were provided over 9 sequential plans of care between 14 and 52 months of age. The child demonstrated improvements in motor control, walked independently at 16.5 months of age, and her Gross Motor Function Measure-88 score increased from 78% to 95% between 27 and 52 months of age.

CONCLUSIONS AND RECOMMENDATIONS FOR CLINICAL PRACTICE

The importance in this case lies in the use of a multisystem approach to treatment, careful consideration of frequency of intervention, and discussion of the unique features of AHC.

Heart rate variability in a patient with alternating hemiplegia

Alternating hemiplegia of childhood (AHC) is a rare disorder characterized by repetitive episodes of transient hemiplegia. Although autonomic nervous system dysfunction is believed to be associated with AHC, there are no reports of heart rate variability (HRV) in patients with AHC. In the current study, we analyzed HRV in a 20-year-old female with this disorder. The frequency of paralytic attacks have decreased since the patient was a teenager, compared to when she was < ten years old; however, as a 20-year-old, she still experiences paralytic attacks several times per month to more than ten times per month. Thus far, she has only suffered paralytic attacks and no epileptic seizures. Using Sanger sequencing, Gly947Arg (2839G>A) in the sodium-potassium (Na⁺/K⁺)-ATPaseα3 subunit gene (ATP1A3) was confirmed from her blood sample. An elevated heart rate lasting one to two minutes and sometimes longer, was primarily observed at night while the patient was sleeping. Large fluctuations in HRV, including low- and high- frequency components, were primarily observed while the patient was sleeping but suppressed during paralytic attacks. These results confirm the presence of an autonomic nervous system disorder in AHC. Because large variation of the autonomic nervous function was observed at night, the pathophysiological function should be investigated for 24 hours.

Alternating Hemiplegia of Childhood in Two Adult Patients with a Mild Syndrome

We describe the cognitive-behavioral functioning of two adult patients with a mild form of alternating hemiplegia of childhood (AHC). AHC is a rare, chronic neurodevelopmental syndrome manifesting in infancy or early childhood, with recurrent hemiplegic or hemidystonic attacks, various nonepileptic paroxysmal events, and cognitive-behavioral impairments, including mental delay of varying degrees. We conducted neurologic and neuroimaging examinations, as well as a neuropsychological assessment, of two men (22 and 30 years old) with mutations in the ATP1A3 gene (p.Leu757Pro and p.Val332Glu) who were experiencing typical AHC transient episodes of alternating weakness or paralysis in order to investigate causes of their poor social functioning. During neurologic examinations of both patients, which were performed between attacks, we observed involuntary movements such as chorea and upper-limb tremor. One patient also had dysarthria. Magnetic resonance imaging revealed no parenchymal brain lesions or atrophy in either patient. Neuropsychological examinations demonstrated near-normal (patient 1) or normal (patient 2) global cognitive functioning, with some isolated executive functioning deficits. Both patients had emotional and social dysfunction as well as difficulties adapting to normal adult life. Although the clinical presentation of AHC is usually dramatic, some patients have mild forms of the syndrome (eg, no significant intellectual disability). However, motor and movement disorders, as well as coexisting emotional-affective abnormalities, may affect these patients' ability to adapt to independent life.

Novel E815K knock-in mouse model of alternating hemiplegia of childhood

De novo mutations causing dysfunction of the ATP1A3 gene, which encodes the α3 subunit of Na⁺/K⁺-ATPase pump expressed in neurons, result in alternating hemiplegia of childhood (AHC). AHC manifests as paroxysmal episodes of hemiplegia, dystonia, behavioral abnormalities, and seizures. The first aim of this study was to characterize a novel knock-in mouse model (Atp1a3^E815K+/-, Matoub, Matb^+/-) containing the E815K mutation of the Atp1a3 gene recognized as causing the most severe and second most common phenotype of AHC with increased morbidity and mortality as compared to other mutations. The second aim was to investigate the effects of flunarizine, currently the most effective drug used in AHC, to further validate our model and to help address a question with significant clinical implications that has not been addressed in prior studies. Specifically, many E815K patients have clinical decompensation and catastrophic regression after discontinuing flunarizine therapy; however, it is not known whether this is congruent with the natural course of the disease and is a result of withdrawal from an acute beneficial effect, withdrawal from a long-term protective effect or from a detrimental effect of prior flunarizine exposure. Our behavioral and neurophysiological testing demonstrated that Matb^+/- mice express a phenotype that bears a strong resemblance to the E815K phenotype in AHC. In addition, these mice developed spontaneous seizures with high incidence of mortality and required fewer electrical stimulations to reach the kindled state as compared to wild-type littermates. Matb^+/- mice treated acutely with flunarizine had reduction in hemiplegic attacks as compared with vehicle-treated mice. After withdrawal of flunarizine, Matb^+/- mice that had received flunarizine did neither better nor worse, on behavioral tests, than those who had received vehicle. We conclude that: 1) Our mouse model containing the E815K mutation manifests clinical and neurophysiological features of the most severe form of AHC, 2) Flunarizine demonstrated acute anti-hemiplegic effects but not long-term beneficial or detrimental behavioral effects after it was stopped, and 3) The Matb^+/- mouse model can be used to investigate the underlying pathophysiology of ATP1A3 dysfunction and the efficacy of potential treatments for AHC.

Deficits in social behavioral tests in a mouse model of alternating hemiplegia of childhood

Social behavioral deficits have been observed in patients diagnosed with alternating hemiplegia of childhood (AHC), rapid-onset dystonia-parkinsonism and CAPOS syndrome, in which specific missense mutations in ATP1A3, encoding the Na⁺, K⁺-ATPase α3 subunit, have been identified. To test the hypothesis that social behavioral deficits represent part of the phenotype of Na⁺, K⁺-ATPase α3 mutations, we assessed the social behavior of the Myshkin mouse model of AHC, which has an I810N mutation identical to that found in an AHC patient with co-morbid autism. Myshkin mice displayed deficits in three tests of social behavior: nest building, pup retrieval and the three-chamber social approach test. Chronic treatment with the mood stabilizer lithium enhanced nest building in wild-type but not Myshkin mice. In light of previous studies revealing a broad profile of neurobehavioral deficits in the Myshkin model – consistent with the complex clinical profile of AHC – our results suggest that Na⁺, K⁺-ATPase α3 dysfunction has a deleterious, but nonspecific, effect on social behavior. By better defining the behavioral profile of Myshkin mice, we identify additional ATP1A3-related symptoms for which the Myshkin model could be used as a tool to advance understanding of the underlying neural mechanisms and develop novel therapeutic strategies.

A randomized, controlled, double-blind, crossover trial of triheptanoin in alternating hemiplegia of childhood

BACKGROUND

Based on the hypothesis of a brain energy deficit, we investigated the safety and efficacy of triheptanoin on paroxysmal episodes in patients with alternating hemiplegia of childhood due to ATP1A3 mutations.

METHODS

We conducted a randomized, double-blind, placebo-controlled crossover study of triheptanoin, at a target dose corresponding to 30% of daily calorie intake, in ten patients with alternating hemiplegia of childhood due to ATP1A3 mutations. Each treatment period consisted of a 12-week fixed-dose phase, separated by a 4-week washout period. The primary outcome was the total number of paroxysmal events. Secondary outcomes included the number of paroxysmal motor-epileptic events; a composite score taking into account the number, severity and duration of paroxysmal events; interictal neurological manifestations; the clinical global impression-improvement scale (CGI-I); and safety parameters. The paired non-parametric Wilcoxon test was used to analyze treatment effects.

RESULTS

In an intention-to-treat analysis, triheptanoin failed to reduce the total number of paroxysmal events (p = 0.646), including motor-epileptic events (p = 0.585), or the composite score (p = 0.059). CGI-I score did not differ between triheptanoin and placebo periods. Triheptanoin was well tolerated.

CONCLUSIONS

Triheptanoin does not prevent paroxysmal events in Alternating hemiplegia of childhood. We show the feasibility of a randomized placebo-controlled trial in this setting.

TRIAL REGISTRATION

The study has been registered with clinicaltrials.gov ( NCT002408354 ) the 03/24/2015.

More Than a Decade of Misdiagnosis of Alternating Hemiplegia of Childhood with Catastrophic Outcome

Alternating hemiplegia of childhood (AHC) is a distinct clinical disorder characterized by recurrent episodes of hemiplegia, abnormal ocular movement, and progressive developmental delay. It is an extremely rare genetic disorder related to ATP1A3 gene mutations. In this paper, we present a case of AHC in which the diagnosis was missed for many years until severe hypoxic brain insult occurred from prolonged status epilepticus. Not only we are presenting an interesting clinical entity and radiological images, but also we are shedding the light on a rare genetic disease with catastrophic sequelae. The challenges in diagnosis and treatment lead to a poor outcome as seen in our case. Although early recognition and accurate diagnosis and treatment of the disease may not change the outcome, counseling of the family may change their expectation and reduce their frustration. Referral to a center with expertise in genetic disorders and access to genetic laboratories is of paramount importance in the diagnosis of this disease. Due to the rarity of this disease in Saudi Arabia, a genotype-phenotype correlation is not feasible.

Alternating Hemiplegia of Childhood: Pharmacological treatment of 30 Italian patients

BACKGROUND

Alternating Hemiplegia of Childhood (AHC) is a severe disorder. Several drugs have been administered as prophylaxis for paroxysmal attacks, however, no therapy is completely effective.

METHODS

Our aim is to review the pharmacological data related to the prophylactic and acute treatment of a cohort of 30 patients (16M, 14F, age range 5-42years) and to correlate them with the clinical and genetic data collected through the Italian Biobank and Clinical Registry for AHC.

RESULTS

Flunarizine was the most commonly used long-term treatment in the cohort; it reduced duration and frequency of attacks in 50% of patients and decreased intensity in 32.1%. In younger patients, flunarizine seemed significantly more effective in reducing intensity. We found no correlation between the effectiveness of flunarizine and genotype, or between developmental outcome and duration of treatment. In particular, 3 of our patients affected by E815K mutation presented rapid neurological deterioration despite ongoing treatment. Among the other administered prophylactic therapies, few proved to be effective (benzodiazepines, niaprazine, acetazolamide, melatonin, olanzapine, ketogenic diet). No clear rationale exists regarding their use, but these therapies may work by reducing the triggering factors.

CONCLUSIONS

The presented data are retrospective, but they are aimed at filling a gap given the rarity of the disease and the lack of randomized and controlled studies. Besides their usefulness in clarifying the pathophysiology of the disease, prospective studies involving larger cohorts of ATP1A3 mutated AHC patients are needed to provide a rationale for testing other molecules.

Diagnosis and Treatment of Alternating Hemiplegia of Childhood

OPINION STATEMENT

The diagnosis and treatment of patients with Alternating Hemiplegia of Childhood (AHC) and related disorders should be provided by a multidisciplinary team experienced with the spectrum of presentations of this disease, with its related disorders, with its complex and fluctuating manifestations, and with cutting edge advances occurring in the field. Involvement in research to advance the understanding of this disease and partnership with international collaborators and family organizations are also important. An example of such an approach is that of The Duke AHC and Related Disorders Multi-Disciplinary Clinic and Program, which, in partnership with the Cure AHC Foundation, has developed and applied this approach to patients seen since early 2013. The program provides comprehensive care and education directly to AHC patients and their families and collaborates with referring physicians on the care of patients with AHC whether evaluated at Duke clinics or not. It also is involved in clinical and basic research and in collaborations with other International AHC Research Consortium (IAHCRC) partners. The clinic is staffed with physicians and experts from Neurology, Cardiology, Child Behavioral Health, Medical Genetics, Neurodevelopment, Neuropsychology, Nursing, Physical and Occupational Therapies, Psychiatry, Sleep Medicine, and Speech/Language Pathology. Patients are seen either for full comprehensive evaluations that last several days or for targeted evaluations with one or few appointments.

Progressive Brain Atrophy in Alternating Hemiplegia of Childhood

Background

Alternating hemiplegia of childhood (AHC) is a rare neurodevelopmental disorder that includes involuntary movements, paroxysmal symptoms, and various severities of nonparoxysmal symptoms.

Objective

To investigate the occurrence of structural brain abnormalities in patients with AHC during clinical courses.

Methods

Conventional brain magnetic resonance imaging findings and clinical courses were retrospectively investigated in 14 patients with AHC confirmed by ATP1A3 mutations.

Results

Progressive frontal dominant cerebral, diffuse cerebellar cortical, and severe hippocampal atrophy were observed in seven patients with irreversible severe motor and intellectual deterioration. All of these seven patients exhibited status epilepticus and required transient respiratory care. Isolated diffuse cerebellar cortical atrophy was observed in two adult patients with mild motor regression. Five patients without apparent deterioration displayed almost normal brain findings.

Conclusions

The areas of atrophy were consistent with the areas of increased expression of the Na⁺/K⁺-ATPase α3 subunit encoded by ATP1A3. Some of paroxysmal and nonparoxysmal neurological symptoms are considered as related to the areas of brain atrophy.

Neurological disease mutations of α3 Na+,K+-ATPase: Structural and functional perspectives and rescue of compromised function

Na⁺,K⁺-ATPase creates transmembrane ion gradients crucial to the function of the central nervous system. The α-subunit of Na⁺,K⁺-ATPase exists as four isoforms (α1-α4). Several neurological phenotypes derive from α3 mutations. The effects of some of these mutations on Na⁺,K⁺-ATPase function have been studied in vitro. Here we discuss the α3 disease mutations as well as information derived from studies of corresponding mutations of α1 in the light of the high-resolution crystal structures of the Na⁺,K⁺-ATPase. A high proportion of the α3 disease mutations occur in the transmembrane sector and nearby regions essential to Na⁺ and K⁺ binding. In several cases the compromised function can be traced to disturbance of the Na⁺ specific binding site III. Recently, a secondary mutation was found to rescue the defective Na⁺ binding caused by a disease mutation. A perspective is that it may be possible to develop an efficient pharmaceutical mimicking the rescuing effect.

Recognizable facial features in patients with alternating hemiplegia of childhood

Alternating hemiplegia of childhood is an early onset neurodevelopmental disorder characterized by paroxystic episodes of alternating hemiplegia, variable degrees of intellectual disability, and dystonic movements. The main causative gene, ATP1A3, is also responsible for other neurodevelopmental disorders. While the neurological profile of this condition is well defined, the question whether a recognizable pattern of physical anomalies does exist in this condition is still open. We performed a morphological evaluation of 30 patients at different ages. All patients were evaluated independently by each author and evaluation sheets were compared, discussed, and agreed afterwards. This study started before the identification of ATP1A3 as the causative gene, and the patients were selected upon their neurological picture. Four of these 30 patients tested negative for ATP1A3 mutations and were excluded from the present work. On physical ground, almost all patients shared a similar physical phenotype consisting of hypotonia, long face, thin eyebrows, strabismus, hypertelorism, long palpebral fissures, downturned mouth, and slender habitus. Such phenotype is sufficiently typical to generate a recognizable gestalt. We also evaluated patients photographs taken from the parents in early childhood (6-20 months) to delineate a clinical profile possibly recognizable before the neurological signs suggest the diagnosis. Our data suggest that the typical early gestalt is sufficient to advise the molecular analysis of ATP1A3, even in absence of the pathognomonic neurological signs. Finally, since a number of patients is now adult, some information can be drawn on the phenotypic evolution of the facial appearance of patients with alternating hemiplegia of childhood. © 2016 Wiley Periodicals, Inc.

Insights into the Pathology of the α3 Na(+)/K(+)-ATPase Ion Pump in Neurological Disorders; Lessons from Animal Models

The transmembrane Na(+)-/K(+) ATPase is located at the plasma membrane of all mammalian cells. The Na(+)-/K(+) ATPase utilizes energy from ATP hydrolysis to extrude three Na(+) cations and import two K(+) cations into the cell. The minimum constellation for an active Na(+)-/K(+) ATPase is one alpha (α) and one beta (β) subunit. Mammals express four α isoforms (α1-4), encoded by the ATP1A1-4 genes, respectively. The α1 isoform is ubiquitously expressed in the adult central nervous system (CNS) whereas α2 primarily is expressed in astrocytes and α3 in neurons. Na(+) and K(+) are the principal ions involved in action potential propagation during neuronal depolarization. The α1 and α3 Na(+)-/K(+) ATPases are therefore prime candidates for restoring neuronal membrane potential after depolarization and for maintaining neuronal excitability. The α3 isoform has approximately four-fold lower Na(+) affinity compared to α1 and is specifically required for rapid restoration of large transient increases in [Na(+)]i. Conditions associated with α3 deficiency are therefore likely aggravated by suprathreshold neuronal activity. The α3 isoform been suggested to support re-uptake of neurotransmitters. These processes are required for normal brain activity, and in fact autosomal dominant de novo mutations in ATP1A3 encoding the α3 isoform has been found to cause the three neurological diseases Rapid Onset Dystonia Parkinsonism (RDP), Alternating Hemiplegia of Childhood (AHC), and Cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS). All three diseases cause acute onset of neurological symptoms, but the predominant neurological manifestations differ with particularly early onset of hemiplegic/dystonic episodes and mental decline in AHC, ataxic encephalopathy and impairment of vision and hearing in CAPOS syndrome and late onset of dystonia/parkinsonism in RDP. Several mouse models have been generated to study the in vivo consequences of Atp1a3 modulation. The different mice show varying degrees of hyperactivity, gait problems, and learning disability as well as stress-induced seizures. With the advent of several Atp1a3-gene or chemically modified animal models that closely phenocopy many aspects of the human disorders, we will be able to reach a much better understanding of the etiology of RDP, AHC, and CAPOS syndrome.

Pediatric migraine variants: a review of epidemiology, diagnosis, treatment, and outcome

Pediatric migraine variants, previously known as childhood periodic syndromes, migraine equivalents, or migraine precursors, are a group of periodic or paroxysmal disorders occurring in patients who also have migraine with or without aura, or who have an increased likelihood of developing migraine. They have common key clinical features including periodic or paroxysmal character, normal neurological examination between attacks, family history of migraine, and clinical evolution to classic types of migraine. This article aims to review the pathophysiology, evaluation, and management of the pediatric migraine variants including abdominal migraine, benign paroxysmal vertigo, cyclic vomiting syndrome, and benign paroxysmal torticollis as well as the episodic syndromes that may lead to migraine, infantile colic, alternating hemiplegia of childhood, and vestibular migraine.

Spontaneously Fluctuating Motor Cortex Excitability in Alternating Hemiplegia of Childhood: A Transcranial Magnetic Stimulation Study

Background

Alternating hemiplegia of childhood is a very rare and serious neurodevelopmental syndrome; its genetic basis has recently been established. Its characteristic features include typically-unprovoked episodes of hemiplegia and other transient or more persistent neurological abnormalities.

Methods

We used transcranial magnetic stimulation to assess the effect of the condition on motor cortex neurophysiology both during and between attacks of hemiplegia. Nine people with alternating hemiplegia of childhood were recruited; eight were successfully tested using transcranial magnetic stimulation to study motor cortex excitability, using single and paired pulse paradigms. For comparison, data from ten people with epilepsy but not alternating hemiplegia, and ten healthy controls, were used.

Results

One person with alternating hemiplegia tested during the onset of a hemiplegic attack showed progressively diminishing motor cortex excitability until no response could be evoked; a second person tested during a prolonged bilateral hemiplegic attack showed unusually low excitability. Three people tested between attacks showed asymptomatic variation in cortical excitability, not seen in controls. Paired pulse paradigms, which probe intracortical inhibitory and excitatory circuits, gave results similar to controls.

Conclusions

We report symptomatic and asymptomatic fluctuations in motor cortex excitability in people with alternating hemiplegia of childhood, not seen in controls. We propose that such fluctuations underlie hemiplegic attacks, and speculate that the asymptomatic fluctuation we detected may be useful as a biomarker for disease activity.

Characterization of cognitive deficits in mice with an alternating hemiplegia-linked mutation

Cognitive impairment is a prominent feature in a range of different movement disorders. Children with Alternating Hemiplegia of Childhood are prone to developmental delay, with deficits in cognitive functioning becoming progressively more evident as they grow older. Heterozygous mutations of the ATP1A3 gene, encoding the Na+,K+-ATPase α3 subunit, have been identified as the primary cause of Alternating Hemiplegia. Heterozygous Myshkin mice have an amino acid change (I810N) in Na+,K+-ATPase α3 that is also found in Alternating Hemiplegia. To investigate whether Myshkin mice exhibit learning and memory deficits resembling the cognitive impairments of patients with Alternating Hemiplegia, we subjected them to a range of behavioral tests that interrogate various cognitive domains. Myshkin mice showed impairments in spatial memory, spatial habituation, locomotor habituation, object recognition, social recognition, and trace fear conditioning, as well as in the visible platform version of the Morris water maze. Increasing the duration of training ameliorated the deficit in social recognition but not in spatial habituation. The deficits of Myshkin mice in all of the learning and memory tests used are consistent with the cognitive impairment of the vast majority of AHC patients. These mice could thus help advance our understanding of the underlying neural mechanisms influencing cognitive impairment in patients with ATP1A3-related disorders.

Transgenic rescue of phenotypic deficits in a mouse model of alternating hemiplegia of childhood

Missense mutations in ATP1A3 encoding Na⁺,K⁺-ATPase α3 are the primary cause of alternating hemiplegia of childhood (AHC). Most ATP1A3 mutations in AHC lie within a cluster in or near transmembrane α-helix TM6, including I810N that is also found in the Myshkin mouse model of AHC. These mutations all substantially reduce Na⁺,K⁺-ATPase α3 activity. Herein, we show that Myshkin mice carrying a wild-type Atp1a3 transgene that confers a 16 % increase in brain-specific total Na⁺,K⁺-ATPase activity show significant phenotypic improvements compared with non-transgenic Myshkin mice. Interventions to increase the activity of wild-type Na⁺,K⁺-ATPase α3 in AHC patients should be investigated further.

Faulty cardiac repolarization reserve in alternating hemiplegia of childhood broadens the phenotype

Alternating hemiplegia of childhood is a rare disorder caused by de novo mutations in the ATP1A3 gene, expressed in neurons and cardiomyocytes. As affected individuals may survive into adulthood, we use the term 'alternating hemiplegia'. The disorder is characterized by early-onset, recurrent, often alternating, hemiplegic episodes; seizures and non-paroxysmal neurological features also occur. Dysautonomia may occur during hemiplegia or in isolation. Premature mortality can occur in this patient group and is not fully explained. Preventable cardiorespiratory arrest from underlying cardiac dysrhythmia may be a cause. We analysed ECG recordings of 52 patients with alternating hemiplegia from nine countries: all had whole-exome, whole-genome, or direct Sanger sequencing of ATP1A3. Data on autonomic dysfunction, cardiac symptoms, medication, and family history of cardiac disease or sudden death were collected. All had 12-lead electrocardiogram recordings available for cardiac axis, cardiac interval, repolarization pattern, and J-point analysis. Where available, historical and prolonged single-lead electrocardiogram recordings during electrocardiogram-videotelemetry were analysed. Half the cohort (26/52) had resting 12-lead electrocardiogram abnormalities: 25/26 had repolarization (T wave) abnormalities. These abnormalities were significantly more common in people with alternating hemiplegia than in an age-matched disease control group of 52 people with epilepsy. The average corrected QT interval was significantly shorter in people with alternating hemiplegia than in the disease control group. J wave or J-point changes were seen in six people with alternating hemiplegia. Over half the affected cohort (28/52) had intraventricular conduction delay, or incomplete right bundle branch block, a much higher proportion than in the normal population or disease control cohort (P = 0.0164). Abnormalities in alternating hemiplegia were more common in those ≥16 years old, compared with those <16 (P = 0.0095), even with a specific mutation (p.D801N; P = 0.045). Dynamic, beat-to-beat or electrocardiogram-to-electrocardiogram, changes were noted, suggesting the prevalence of abnormalities was underestimated. Electrocardiogram changes occurred independently of seizures or plegic episodes. Electrocardiogram abnormalities are common in alternating hemiplegia, have characteristics reflecting those of inherited cardiac channelopathies and most likely amount to impaired repolarization reserve. The dynamic electrocardiogram and neurological features point to periodic systemic decompensation in ATP1A3-expressing organs. Cardiac dysfunction may account for some of the unexplained premature mortality of alternating hemiplegia. Systematic cardiac investigation is warranted in alternating hemiplegia of childhood, as cardiac arrhythmic morbidity and mortality are potentially preventable.

A functional correlate of severity in alternating hemiplegia of childhood

OBJECTIVE

Mutations in ATP1A3, the gene that encodes the α3 subunit of the Na(+)/K(+) ATPase, are the primary cause of alternating hemiplegia of childhood (AHC). Correlations between different mutations and AHC severity were recently reported, with E815K identified in severe and D801N and G947R in milder cases. This study aims to explore the molecular pathological mechanisms in AHC and to identify functional correlates for mutations associated with different levels of disease severity.

METHODS

Human wild type ATP1A3, and E815K, D801N and G947R mutants were expressed in Xenopus laevis oocytes and Na(+)/K(+) ATPase function measured. Structural homology models of the human α3 subunit containing AHC mutations were created.

RESULTS

The AHC mutations examined all showed similar levels of reduction in forward cycling. Wild type forward cycling was reduced by coexpression with any mutant, indicating dominant negative interactions. Proton transport was measured and found to be selectively impaired only in E815K. Homology modeling showed that D801 and G947 lie within or near known cation binding sites while E815 is more distal. Despite its effect on proton transport, E815K was also distant from the proposed proton transport route.

INTERPRETATION

Loss of forward cycling and dominant negativity are common and likely necessary pathomechanisms for AHC. In addition, loss of proton transport correlated with severity of AHC. D801N and G947R are likely to directly disrupt normal Na(+)/K(+) binding while E815K may disrupt forward cycling and proton transport via allosteric mechanisms yet to be elucidated.

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.

Rapid-onset dystonia-parkinsonism associated with the I758S mutation of the ATP1A3 gene: a neuropathologic and neuroanatomical study of four siblings

Rapid-onset dystonia-parkinsonism (RDP) is a movement disorder associated with mutations in the ATP1A3 gene. Signs and symptoms of RDP commonly occur in adolescence or early adulthood and can be triggered by physical or psychological stress. Mutations in ATP1A3 are also associated with alternating hemiplegia of childhood (AHC). The neuropathologic substrate of these conditions is unknown. The central nervous system of four siblings, three affected by RDP and one asymptomatic, all carrying the I758S mutation in the ATP1A3 gene, was analyzed. This neuropathologic study is the first carried out in ATP1A3 mutation carriers, whether affected by RDP or AHC. Symptoms began in the third decade of life for two subjects and in the fifth for another. The present investigation aimed at identifying, in mutation carriers, anatomical areas potentially affected and contributing to RDP pathogenesis. Comorbid conditions, including cerebrovascular disease and Alzheimer disease, were evident in all subjects. We evaluated areas that may be relevant to RDP separately from those affected by the comorbid conditions. Anatomical areas identified as potential targets of I758S mutation were globus pallidus, subthalamic nucleus, red nucleus, inferior olivary nucleus, cerebellar Purkinje and granule cell layers, and dentate nucleus. Involvement of subcortical white matter tracts was also evident. Furthermore, in the spinal cord, a loss of dorsal column fibers was noted. This study has identified RDP-associated pathology in neuronal populations, which are part of complex motor and sensory loops. Their involvement would cause an interruption of cerebral and cerebellar connections which are essential for maintenance of motor control.

Distinct neurological disorders with ATP1A3 mutations

Genetic research has shown that mutations that modify the protein-coding sequence of ATP1A3, the gene encoding the α3 subunit of Na(+)/K(+)-ATPase, cause both rapid-onset dystonia parkinsonism and alternating hemiplegia of childhood. These discoveries link two clinically distinct neurological diseases to the same gene, however, ATP1A3 mutations are, with one exception, disease-specific. Although the exact mechanism of how these mutations lead to disease is still unknown, much knowledge has been gained about functional consequences of ATP1A3 mutations using a range of in-vitro and animal model systems, and the role of Na(+)/K(+)-ATPases in the brain. Researchers and clinicians are attempting to further characterise neurological manifestations associated with mutations in ATP1A3, and to build on the existing molecular knowledge to understand how specific mutations can lead to different diseases.

ATP1A3 mutations and genotype-phenotype correlation of alternating hemiplegia of childhood in Chinese patients

Alternating hemiplegia of childhood (AHC) is a rare and severe neurological disorder. ATP1A3 was recently identified as the causative gene. Here we report the first genetic study in Chinese AHC cohort. We performed whole-exome sequencing on three trios and three unrelated patients, and screened additional 41 typical cases and 100 controls by PCR-Sanger sequencing. ATP1A3 mutations were detected in 95.7% of typical AHC patients. At least 93.3% were de novo. Four late onset, atypical AHC patients were also mutation positive, suggesting the need for testing ATP1A3 mutations in atypical cases. Totally, 13 novel missense mutations (T370N, G706R, L770R, T771N, T771I, S772R, L802P, D805H, M806K, P808L, I810N, L839P and G893R) were identified in our study. By homology modeling of the mutant protein structures and calculation of an extensive list of molecular features, we identified two statistically significant molecular features, solvent accessibility and distance to metal ion, that distinguished disease-associated mutations from neutral variants. A logistic regression classifier achieved 92.9% accuracy by the average of 100 times of five-fold cross validations. Genotype-phenotype correlation analysis showed that patients with epilepsy were more likely to carry E815K mutation. In summary, ATP1A3 is the major pathogenic gene of AHC in Chinese patients; mutations have distinctive molecular features that discriminate them from neutral variants and are correlated with phenotypes.

Alternating hemiplegia of childhood: new diagnostic options

A syndrome of alternating hemiplegia of childhood (AHC) is a rare disorder first presented in 1971. AHC is characterized by transient episodes of hemiplegia affecting either one or both sides of the body. Age of onset is before 18 months and the common earliest manifestations are dystonic or tonic attacks and nystagmus. Hemiplegic episodes last minutes to days and the frequency and duration tend to decrease with time. Motor and intellectual development is affected, deficits may also develop later. Epileptic seizures occur in some patients. Neuroimaging of the brain usually reveals no abnormalities. The variability of individual clinical presentations and evolution of symptoms have made diagnosis difficult. Therefore the problems of misdiagnosis could account for the low prevalence of this syndrome. This paper hopes to present actual data on AHC, especially of the results of genetic research and new diagnostic tools.

Alternating hemiplegia of childhood in Denmark: clinical manifestations and ATP1A3 mutation status

Alternating hemiplegia of childhood (AHC) is a rare neurodevelopmental disorder characterized by early-onset recurrent distinctive hemiplegic episodes commonly accompanied by other paroxysmal features and developmental impairment. De novo mutations in ATP1A3 were recently identified as a genetic cause of AHC. To describe the entire Danish cohort of paediatric AHC patients we approached neuropaediatricians nationwide. All currently acknowledged Danish patients ≤16 years with AHC were genetically tested and seen by the same child neurologist (PU). Ten patients; seven girls and three boys were identified. Mean present age was 10.0 years (range 1-16). Mean age at presentation was 7.4 months (range 1-18 months). Sequencing of ATP1A3 in all ten patients revealed a pathogenic mutation in seven. Two females with moderate psychomotor impairment were heterozygous for the known p.G947R mutation, whereas one severely retarded boy was heterozygous for the common p.E815K mutation. The prevalent p.D801N mutation was identified in two moderate to severely retarded children. Interestingly, in a set of monochorionic male twins a novel p.D801E mutation was identified, underscoring that the asparagine at position 801 is a mutation hotspot. Three girls aged 5-13 years did not reveal any ATP1A3 mutations. They were rather mildly clinically affected and displayed a normal or near-normal psychomotor development. This is the first study of AHC in the Danish paediatric population. The patients harboured a wide range of psychomotor difficulties. Patients with no mutation detected tended to be less severely affected. Prevalence was approximately 1 per 100,000 children.

Asystole in alternating hemiplegia with de novo ATP1A3 mutation

Alternating hemiplegia is a rare condition presenting with episodes of hemiplegia, epileptic seizures and, at times, dysautonomic attacks. De novo ATP1A3 (Na(+)/K(+) ATPase subunit) mutations were recently found to be the most common cause. We report a patient with alternating hemiplegia with de novo ATP1A3 mutation who experienced new-onset episodes of collapse in early adulthood unrelated to seizures. An implantable cardiac loop recorder documented episodes of asystole up to 5 s long. Subsequently a permanent pacemaker was implanted. ATP1A3 heart expression may be the explanation for the association of alternating hemiplegia and asystole episodes. Alternating hemiplegia has been associated with an increased risk of sudden death and lethal cardiac arrhythmias may be causative. Patients may need referral for appropriate cardiac investigations, especially if there is a change in symptoms. This case highlights the importance of clinical vigilance in patients with alternating hemiplegia.

Episodic neurologic disorders: syndromes, genes, and mechanisms

Many neurologic diseases cause discrete episodic impairment in contrast with progressive deterioration. The symptoms of these episodic disorders exhibit striking variety. Herein we review what is known of the phenotypes, genetics, and pathophysiology of episodic neurologic disorders. Of these, most are genetically complex, with unknown or polygenic inheritance. In contrast, a fascinating panoply of episodic disorders exhibit Mendelian inheritance. We classify episodic Mendelian disorders according to the primary neuroanatomical location affected: skeletal muscle, cardiac muscle, neuromuscular junction, peripheral nerve, or central nervous system (CNS). Most known Mendelian mutations alter genes that encode membrane-bound ion channels. These mutations cause ion channel dysfunction, which ultimately leads to altered membrane excitability as manifested by episodic disease. Other Mendelian disease genes encode proteins essential for ion channel trafficking or stability. These observations have cemented the channelopathy paradigm, in which episodic disorders are conceptualized as disorders of ion channels. However, we expand on this paradigm to propose that dysfunction at the synaptic and neuronal circuit levels may underlie some episodic neurologic entities.

Lack of SLC2A1 (glucose transporter 1) mutations in 30 Italian patients with alternating hemiplegia of childhood

Alternating hemiplegia of childhood is a rare, predominantly sporadic disorder. Diagnosis is clinical, and little is known about genetics. Glucose transporter 1 deficiency syndrome shares with alternating hemiplegia of childhood paroxysmal and nonparoxysmal symptoms. The aim of the study was to investigate glucose transporter 1 mutations in 30 Italian patients. Genetic material was analyzed by DNA amplification and glucose transporter 1 region sequencing. Mutational analysis findings of the SLC2A1 gene were negative in all patients. The pattern of movement disorders was reviewed. Interictal dystonia and multiple paroxysmal events were typical of alternating hemiplegia of childhood. In conclusion, alternating hemiplegia of childhood is a heterogeneous clinical condition, and although glucose transporter 1 deficiency can represent an undiagnosed cause of this disorder, mutational analysis is not routinely recommended. Alternatively, a careful clinical analysis and the 3-O-methyl-D-glucose uptake test can allow prompt identification of a subgroup of patients with alternating hemiplegia of childhood treatable with a ketogenic diet.

Alternating hemiplegia of childhood-related neural and behavioural phenotypes in Na+,K+-ATPase α3 missense mutant mice

Missense mutations in ATP1A3 encoding Na⁺,K⁺-ATPase α3 have been identified as the primary cause of alternating hemiplegia of childhood (AHC), a motor disorder with onset typically before the age of 6 months. Affected children tend to be of short stature and can also have epilepsy, ataxia and learning disability. The Na⁺,K⁺-ATPase has a well-known role in maintaining electrochemical gradients across cell membranes, but our understanding of how the mutations cause AHC is limited. Myshkin mutant mice carry an amino acid change (I810N) that affects the same position in Na⁺,K⁺-ATPase α3 as I810S found in AHC. Using molecular modelling, we show that the Myshkin and AHC mutations display similarly severe structural impacts on Na⁺,K⁺-ATPase α3, including upon the K⁺ pore and predicted K⁺ binding sites. Behavioural analysis of Myshkin mice revealed phenotypic abnormalities similar to symptoms of AHC, including motor dysfunction and cognitive impairment. 2-DG imaging of Myshkin mice identified compromised thalamocortical functioning that includes a deficit in frontal cortex functioning (hypofrontality), directly mirroring that reported in AHC, along with reduced thalamocortical functional connectivity. Our results thus provide validation for missense mutations in Na⁺,K⁺-ATPase α3 as a cause of AHC, and highlight Myshkin mice as a starting point for the exploration of disease mechanisms and novel treatments in AHC.

Identification of ATP1A3 mutations by exome sequencing as the cause of alternating hemiplegia of childhood in Japanese patients

Background

Alternating hemiplegia of childhood (AHC) is a rare disorder characterized by transient repeated attacks of paresis and cognitive impairment. Recent studies from the U.S. and Europe have described ATP1A3 mutations in AHC. However, the genotype-phenotype relationship remains unclear. The purpose of this study was to identify the genetic abnormality in a Japanese cohort of AHC using exome analysis.

Principal Findings

A total of 712,558 genetic single nucleotide variations in 8 patients with sporadic AHC were found. After a series of exclusions, mutations of three genes were regarded as candidate causes of AHC. Each patient harbored a heterozygous missense mutation of ATP1A3, which included G755C, E815K, C927Y and D801N. All mutations were at highly conserved amino acid residues and deduced to affect ATPase activity of the corresponding ATP pump, the product of ATP1A3. They were de novo mutations and not identified in 96 healthy volunteers. Using Sanger sequencing, E815K was found in two other sporadic cases of AHC. In this study, E815K was found in 5 of 10 patients (50%), a prevalence higher than that reported in two recent studies [19 of 82 (23%) and 7 of 24 (29%)]. Furthermore, the clinical data of the affected individuals indicated that E815K resulted in a severer phenotype compared with other ATP1A3 mutations.

Interpretation

Heterozygous de novo mutations of ATP1A3 were identified in all Japanese patients with AHC examined in this study, confirming that ATP1A3 mutation is the cause of AHC.

Alternating hemiplegia of childhood

Alternating hemiplegia of childhood (AHC) is a very rare disease characterized by recurrent attacks of loss of muscular tone resulting in hypomobility of one side of the body. The etiology of the disease due to ATP1A3 gene mutations in the majority of patients. Few familial cases have been described. AHC has an onset in the first few months of life. Hemiplegic episodes are often accompanied by other paroxysmal manifestations, such as lateral eyes and head deviation toward the hemiplegic side and a very peculiar monocular nystagmus. As the attack progresses, hemiplegia can shift to the other side of the body. Sometimes the attack can provoke bilateral paralysis, and these patients may have severe clinical impairment, with difficulty in swallowing and breathing. Hemiplegic attacks may be triggered by different stimuli, like bath in warm water, motor activity, or emotion. The frequency of attacks is high, usually several in a month or in a week. The duration is variable from a few minutes to several hours or even days. Sleep can stop the attack. Movement disorders such as dystonia and abnormal movements are frequent. Cognitive delay of variable degree is a common feature. Epilepsy has been reported in 50% of the cases, but seizure onset is usually during the third or fourth year of life. Many drugs have been used in AHC with very few results. Flunarizine has the most supportive anecdotal evidence regarding efficacy.