Absence of small-vessel abnormalities in alternating hemiplegia of childhood

[Alternating hemiplegia with epilepsy]

A clinical case of a genetically confirmed diagnosis of alternating hemiplegia associated with epilepsy is presented. The combination of two types of seizures in a child made it difficult to make a diagnosis. The result of video-EEG monitoring made it possible to understand that a child showed both epileptic seizures and non-epileptic seizures simultaneously with different periodicities. The mutation in the ATP1A3 gene was verified with genome-wide sequencing and targeted therapy was prescribed in a timely manner. As a result, both types of seizures stopped after treatment.

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.

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.

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 chinese following long-term treatment with flunarizine or topiramate

OBJECTIVE

Alternating hemiplegia of childhood (AHC) is a rare and intractable disorder. The etiology and standard therapy of AHC remain unknown. The long-term effects of flunarizine or topiramate on patients with AHC are still not clear.

METHODS

Fifteen patients were investigated in this study. Their neurological disturbance and mental retardation after drug therapy were evaluated.

RESULTS

Nine patients treated with flunarizine therapy and three children with topimarate treatment presented with shorter duration or less frequency of the hemiplegic attacks. These drug responsive patients also showed improvements on neurological disturbance including eye movement disorder, choreoathetotic movements, dystonia, and ataxia. However, seizure episodes and cognitive impairments were not alleviated in AHC with long-term drug therapy.

CONCLUSIONS

The findings from the present study support flunarizine or topitamate as the rational treatment for AHC.