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

Excellent Response to a Ketogenic Diet in a Patient with Alternating Hemiplegia of Childhood

International audienceAlternating hemiplegia of childhood (AHC) is a rare disorder caused by heterozygous mutations in ATP1A3. AHC is associated with early-onset plegic and tonic/dystonic attacks and permanent neurologic deficits. Attacks tend to persist through life. Flunarizine therapy occasionally reduces the severity, duration and frequency of attacks. A ketogenic diet/modified Atkins diet (KD/MAD) can attenuate paroxysmal movement disorders associated with GLUT1 deficiency syndrome (GLUT1DS), but there are no reports on the effect of KD/MAD in AHC. We describe the case of a young girl with AHC who had tonic/dystonic and plegic attacks, mostly triggered by exercise, together with mild permanent dystonia and mental retardation. Her family had a history of dominant (three affected generations) paroxysmal exercise-induced dystonia. A history of plegic attacks that ceased after childhood was retraced from the medical records of the three affected adults, leading to the diagnosis of familial AHC due to ATP1A3 p.Asp923Asn mutation (Roubergue et al 2013). KD/MAD was considered for the proband when she was 3½ years old, following initial misdiagnosis of GLUT1DS. MAD, a KD variant, was chosen because it is easier to manage than KD and is similarly effective to KD in most GLUT1DS patients. MAD resulted in complete disappearance of the attacks during 15 months of follow-up. A modified Atkins diet had a sustained beneficial effect on attacks associated with AHC. Although preliminary, this observation suggests that a ketogenic diet might be a therapeutic option for paroxysmal disorders in some patients with alternating hemiplegia of childhood

De novo mutations in ATP1A3 cause alternating hemiplegia of childhood

Alternating hemiplegia of childhood (AHC) is a rare, severe neurodevelopmental syndrome characterized by recurrent hemiplegic episodes and distinct neurological manifestations. AHC is usually a sporadic disorder and has unknown etiology. We used exome sequencing of seven patients with AHC and their unaffected parents to identify de novo nonsynonymous mutations in ATP1A3 in all seven individuals. In a subsequent sequence analysis of ATP1A3 in 98 other patients with AHC, we found that ATP1A3 mutations were likely to be responsible for at least 74% of the cases; we also identified one inherited mutation in a case of familial AHC. Notably, most AHC cases are caused by one of seven recurrent ATP1A3 mutations, one of which was observed in 36 patients. Unlike ATP1A3 mutations that cause rapid-onset dystonia-parkinsonism, AHC-causing mutations in this gene caused consistent reductions in ATPase activity without affecting the level of protein expression. This work identifies de novo ATP1A3 mutations as the primary cause of AHC and offers insight into disease pathophysiology by expanding the spectrum of phenotypes associated with mutations in ATP1A3