A Distinct Phenotype in a Novel ATP1A3 Mutation: Connecting the Two Ends of a Spectrum

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.

The Phenotypic Continuum of ATP1A3-Related Disorders

BACKGROUND AND OBJECTIVES

ATP1A3 is associated with a broad spectrum of predominantly neurologic disorders, which continues to expand beyond the initially defined phenotypes of alternating hemiplegia of childhood, rapid-onset dystonia parkinsonism, and cerebellar ataxia, areflexia, pes cavus, optic atrophy, sensorineural hearing loss syndrome. This phenotypic variability makes it challenging to assess the pathogenicity of an ATP1A3 variant found in an undiagnosed patient. We describe the phenotypic features of individuals carrying a pathogenic/likely pathogenic ATP1A3 variant and perform a literature review of all ATP1A3 variants published thus far in association with human neurologic disease. Our aim is to demonstrate the heterogeneous clinical spectrum of the gene and look for phenotypic overlap between patients that will streamline the diagnostic process.

METHODS

Undiagnosed individuals with ATP1A3 variants were identified within the cohort of the Deciphering Developmental Disorders study with additional cases contributed by collaborators internationally. Detailed clinical data were collected with consent through a questionnaire completed by the referring clinicians. PubMed was searched for publications containing the term "ATP1A3" from 2004 to 2021.

RESULTS

Twenty-four individuals with a previously undiagnosed neurologic phenotype were found to carry 21 ATP1A3 variants. Eight variants have been previously published. Patients experienced on average 2-3 different types of paroxysmal events. Permanent neurologic features were common including microcephaly (7; 29%), ataxia (13; 54%), dystonia (10; 42%), and hypotonia (7; 29%). All patients had cognitive impairment. Neuropsychiatric diagnoses were reported in 16 (66.6%) individuals. Phenotypes were extremely varied, and most individuals did not fit clinical criteria for previously published phenotypes. On review of the literature, 1,108 individuals have been reported carrying 168 different ATP1A3 variants. The most common variants are associated with well-defined phenotypes, while more rare variants often result in very rare symptom correlations, such as are seen in our study. Combined Annotation-Dependent Depletion (CADD) scores of pathogenic and likely pathogenic variants were significantly higher and variants clustered within 6 regions of constraint.

DISCUSSION

Our study shows that looking for a combination of paroxysmal events, hyperkinesia, neuropsychiatric symptoms, and cognitive impairment and evaluating the CADD score and variant location can help identify an ATP1A3-related condition, rather than applying diagnostic criteria alone.

ATP1A3 mutation in rapid-onset dystonia parkinsonism: New data and genotype-phenotype correlation analysis

Background

Rapid-onset dystonia parkinsonism (RDP) is a rare disease caused by ATP1A3 mutation with considerable clinical heterogeneity. Increased knowledge of RDP could be beneficial in its early diagnosis and treatment.

Objective

This study aimed to summarize the gene mutation spectrum of ATP1A3 associated with RDP, and to explore the correlation of ATP1A3 variants with RDP clinical phenotypes.

Methods

In this study, we reported two RDP patients from a family with a novel inherited ATP1A3 variant. Then, we reviewed and analyzed the available literature in English focused on ATP1A3-causative RDP. A total of 35 articles covering 15 families (59 patients) and 36 sporadic RDP cases were included in our analysis.

Results

The variant A813V (2438C>T) in ATP1A3 found in our cases was a novel mutant. Delays in diagnosis were common, with a mean delay time of 14 years. ATP1A3 had distinct RDP-related mutation hotspots, which consisted of exon8, 14, 17, and 18, and the most frequently occurring variants were T613M and I578S. Approximately 74.5% of patients have specific triggers before disease onset, and 82.1% of RDPs have stable symptoms within 1 month. The incidence rates of dystonia and bradykinesia are 100 and 88.1%, respectively. The onset site varied and exhibited a rostrocaudal gradient distribution pattern in 45% of patients with RDP. Approximately 63.6% of patients had mild improvement after receiving comprehensive interventions, especially in gait disturbance amelioration.

Conclusion

In patients with acute and unexplained dystonia or bradykinesia, gene screening on ATP1A3 should be timely performed. When a diagnosis has been made, treatments that may be effective are to be attempted. Our study would be helpful for the early diagnosis and treatment of ATP1T3-related RDP.

Alternating Hemiplegia of Childhood: Understanding the Genotype-Phenotype Relationship of ATP1A3 Variations

Alternating hemiplegia of childhood (AHC) is a rare neurological disorder affecting children with an onset before 18 months. Diagnostic clues include transient episodes of hemiplegia alternating in the laterality or quadriparesis, nystagmus and other paroxysmal attacks as tonic and dystonic spells. Epilepsy is also a common feature. In the past, a great effort has been done to understand the genetic basis of the disease leading to the discovery of mutations in the ATP1A3 gene encoding for the alpha3 subunit of Na⁺/K⁺ATPase, a protein already related to another disease named Rapid Onset Dystonia Parkinsonism (RDP). ATP1A3 mutations account for more than 70% of cases of AHC. In particular, three hotspot mutations account for about 60% of all cases, and these data have been confirmed in large population studies. Specifically, the p.Asp801Asn variant has been found to cause 30–43% of all cases, p.Glu815Lys is responsible for 16–35% of cases and p.Gly947Arg accounts for 8–15%. These three mutations are associated with different clinical phenotype in terms of symptoms, severity and prognosis. In vitro and in vivo models reveal that a crucial role of Na⁺/K⁺ATPase pump activity emerges in maintaining a correct membrane potential, survival and homeostasis of neurons. Herein, we attempt to summarize all clinical, genetic and molecular aspects of AHC considering ATP1A3 as its primary disease-causing determinant.