A novel ATP1A2 gene mutation in an Irish familial hemiplegic migraine kindred

Unravelling the Genetic Landscape of Hemiplegic Migraine: Exploring Innovative Strategies and Emerging Approaches

Migraine is a severe, debilitating neurovascular disorder. Hemiplegic migraine (HM) is a rare and debilitating neurological condition with a strong genetic basis. Sequencing technologies have improved the diagnosis and our understanding of the molecular pathophysiology of HM. Linkage analysis and sequencing studies in HM families have identified pathogenic variants in ion channels and related genes, including CACNA1A, ATP1A2, and SCN1A, that cause HM. However, approximately 75% of HM patients are negative for these mutations, indicating there are other genes involved in disease causation. In this review, we explored our current understanding of the genetics of HM. The evidence presented herein summarises the current knowledge of the genetics of HM, which can be expanded further to explain the remaining heritability of this debilitating condition. Innovative bioinformatics and computational strategies to cover the entire genetic spectrum of HM are also discussed in this review.

Functional correlation of ATP1A2 mutations with phenotypic spectrum: from pure hemiplegic migraine to its variant forms

Background

Mutations in ATP1A2, the gene encoding the α2 subunit of Na⁺/K⁺-ATPase, are the main cause of familial hemiplegic migraine type 2 (FHM2). The clinical presentation of FHM2 with mutations in the same gene varies from pure FHM to severe forms with epilepsy and intellectual disability, but the correlation of these symptoms with different ATP1A2 mutations is still unclear.

Methods

Ten ATP1A2 missense mutations were selected according to different phenotypes of FHM patients. They caused pure FHM (FHM: R65W, R202Q, R593W, G762S), FHM with epilepsy (FHME: R548C, E825K, R938P), or FHM with epilepsy and intellectual disability (FHMEI: T378N, G615R, D718N). After ouabain resistance and fluorescence modification, plasmids carrying those mutations were transiently transfected into HEK293T and HeLa cells. The biochemical functions were studied including cell survival assays, membrane protein extraction, western blotting, and Na⁺/K⁺-ATPase activity tests. The electrophysiological functions of G762S, R938P, and G615R mutations were investigated in HEK293T cells using whole-cell patch-clamp. Homology modeling was performed to determine the locational distribution of ATP1A2 mutations.

Results

Compared with wild-type pumps, all mutations showed a similar level of protein expression and decreased cell viability in the presence of 1 µM ouabain, and there was no significant difference among the mutant groups. The changes in Na⁺/K⁺-ATPase activity were correlated with the severity of FHM phenotypes. In the presence of 100 µM ouabain, the Na⁺/K⁺-ATPase activity was FHM > FHME > FHMEI. The ouabain-sensitive Na⁺/K⁺-ATPase activity of each mutant was significantly lower than that of the wild-type protein, and there was no significant difference among all mutant groups. Whole-cell voltage-clamp recordings in HEK293T cells showed that the ouabain-sensitive pump currents of G615R were significantly reduced, while those of G762S and R938P were comparable to those of the wild-type strain.

Conclusions

ATP1A2 mutations cause phenotypes ranging from pure FHM to FHM with epilepsy and intellectual disability due to varying degrees of deficits in biochemical and electrophysiological properties of Na⁺/K⁺-ATPase. Mutations associated with intellectual disability presented with severe impairment of Na⁺/K⁺-ATPase. Whether epilepsy is accompanied, or the type of epilepsy did not seem to affect the degree of impairment of pump function.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-021-01309-4.

Serial magnetic resonance imaging findings during severe attacks of familial hemiplegic migraine type 2: a case report

BACKGROUND

Hemiplegic migraines represent a heterogeneous disorder with various presentations. Hemiplegic migraines are classified as sporadic or familial based on the presence of family history, but both subtypes have an underlying genetic etiology. Mutations in the ATP1A2 gene are responsible for Familial Hemiplegic type 2 (FHM2) or the sporadic hemiplegic migraine (SHM) counterpart if there is no family history of the disorder. Manifestations include migraine with aura and hemiparesis along with a variety of other symptoms likely dependent upon the specific mutation(s) present.

CASE PRESENTATION

We report the case of an adult man who presented with headache, aphasia, and right-sided weakness. Workup for stroke and various infectious agents was unremarkable during the patient's extended hospital stay. We emphasize the changes in the Magnetic Resonance Imaging (MRI) over time and the delay from onset of symptoms to MRI changes in Isotropic Diffusion Map (commonly referred to as Diffusion Weighted Imaging (DWI)) as well as Apparent Diffusion Coefficient (ADC).

CONCLUSIONS

We provide a brief review of imaging findings correlated with signs/symptoms and specific mutations in the ATP1A2 gene reported in the literature. Description of the various mutations and consequential presentations may assist neurologists in identifying cases of Hemiplegic Migraine, which may include transient changes in ADC and DWI imaging throughout the course of an attack.

The Integrative Method Based on the Module-Network for Identifying Driver Genes in Cancer Subtypes

With advances in next-generation sequencing(NGS) technologies, a large number of multiple types of high-throughput genomics data are available. A great challenge in exploring cancer progression is to identify the driver genes from the variant genes by analyzing and integrating multi-types genomics data. Breast cancer is known as a heterogeneous disease. The identification of subtype-specific driver genes is critical to guide the diagnosis, assessment of prognosis and treatment of breast cancer. We developed an integrated frame based on gene expression profiles and copy number variation (CNV) data to identify breast cancer subtype-specific driver genes. In this frame, we employed statistical machine-learning method to select gene subsets and utilized an module-network analysis method to identify potential candidate driver genes. The final subtype-specific driver genes were acquired by paired-wise comparison in subtypes. To validate specificity of the driver genes, the gene expression data of these genes were applied to classify the patient samples with 10-fold cross validation and the enrichment analysis were also conducted on the identified driver genes. The experimental results show that the proposed integrative method can identify the potential driver genes and the classifier with these genes acquired better performance than with genes identified by other methods.

Familial Hemiplegic Migraine with Severe Attacks: A New Report with ATP1A2 Mutation

Introduction. Familial hemiplegic migraine (FHM) is a rare disorder characterized by migraine attacks with motor weakness during the aura phase. Mutations in CACNA1A, ATP1A2, SCN1A, and PRRT2 genes have been described. Methods. To describe a mutation in ATP1A2 gene in a FHM case with especially severe and prolonged symptomatology. Results. 22-year-old woman was admitted due to migraine-type headache and sudden onset of right-sided weakness and aphasia; she had similar episodes in her childhood. Her mother was diagnosed with hemiplegic migraine without genetic confirmation. She presented with fever, decreased consciousness, left gaze preference, mixed aphasia, right facial palsy, right hemiplegia, and left crural paresis. Computed tomography (CT) showed no lesion and CT perfusion study evidenced oligohemia in left hemisphere. A normal brain magnetic resonance (MR) was obtained. Impaired consciousness and dysphasia began to improve three days after admission and mild dysphasia and right hemiparesis lasted for 10 days. No recurrences were reported during a follow-up of two years. We identified a variant in heterozygous state in ATP1A2 gene (p.Thr364Met), pathogenic according to different prediction algorithms (SIFT, PolyPhen2, MutationTaster, and Condel). Conclusion. Prolonged and severe attacks with diffuse hypoperfusion in a FHM seemed to be specially related to ATP1A2 mutations, and p.T364M should be considered.

Importance of a Potential Protein Kinase A Phosphorylation Site of Na+,K+-ATPase and Its Interaction Network for Na+ Binding

The molecular mechanism underlying PKA-mediated regulation of Na(+),K(+)-ATPase was explored in mutagenesis studies of the potential PKA site at Ser-938 and surrounding charged residues. The phosphomimetic mutations S938D/E interfered with Na(+) binding from the intracellular side of the membrane, whereas Na(+) binding from the extracellular side was unaffected. The reduction of Na(+) affinity is within the range expected for physiological regulation of the intracellular Na(+) concentration, thus supporting the hypothesis that PKA-mediated phosphorylation of Ser-938 regulates Na(+),K(+)-ATPase activity in vivo Ser-938 is located in the intracellular loop between transmembrane segments M8 and M9. An extended bonding network connects this loop with M10, the C terminus, and the Na(+) binding region. Charged residues Asp-997, Glu-998, Arg-1000, and Lys-1001 in M10, participating in this bonding network, are crucial to Na(+) interaction. Replacement of Arg-1005, also located in the vicinity of Ser-938, with alanine, lysine, methionine, or serine resulted in wild type-like Na(+) and K(+) affinities and catalytic turnover rate. However, when combined with the phosphomimetic mutation S938E only lysine substitution of Arg-1005 was compatible with Na(+),K(+)-ATPase function, and the Na(+) affinity of this double mutant was reduced even more than in single mutant S938E. This result indicates that the positive side chain of Arg-1005 or the lysine substituent plays a mechanistic role as interaction partner of phosphorylated Ser-938, transducing the phosphorylation signal into a reduced affinity of Na(+) site III. Electrostatic interaction of Glu-998 is of minor importance for the reduction of Na(+) affinity by phosphomimetic S938E as revealed by combining S938E with E998A.

Migraine genetics: current findings and future lines of research

In the last two decades, migraine research has greatly advanced our current knowledge of the genetic contributions and the pathophysiology of this common and debilitating disorder. Nonetheless, this knowledge still needs to grow further and to translate into more effective treatments. To date, several genes involved in syndromic and monogenic forms of migraine have been identified, allowing the generation of animal models which have significantly contributed to current knowledge of the mechanisms underlying these rare forms of migraine. Common forms of migraine are instead posing a greater challenge, as they may most often stem from complex interactions between multiple common genetic variants, with environmental triggers. This paper reviews our current understanding of migraine genetics, moving from syndromic and monogenic forms to oligogenic/polygenic migraines most recently addressed with some success through genome-wide association studies. Methodological issues in study design and future perspectives opened by biomarker research will also be briefly addressed.

Functional analysis of human Na+/K+-ATPase familial or sporadic hemiplegic migraine mutations expressed in Xenopus oocytes

AIM: Functional characterization of ATP1A2 mutations that are related to familial or sporadic hemiplegic migraine (FHM2, SHM).

METHODS: cRNA of human Na⁺/K⁺-ATPase α₂- and β₁-subunits were injected in Xenopus laevis oocytes. FHM2 or SHM mutations of residues located in putative α/β interaction sites or in the α₂-subunit’s C-terminal region were investigated. Mutants were analyzed by the two-electrode voltage-clamp (TEVC) technique on Xenopus oocytes. Stationary K⁺-induced Na⁺/K⁺ pump currents were measured, and the voltage dependence of apparent K⁺ affinity was investigated. Transient currents were recorded as ouabain-sensitive currents in Na⁺ buffers to analyze kinetics and voltage-dependent pre-steady state charge translocations. The expression of constructs was verified by preparation of plasma membrane and total membrane fractions of cRNA-injected oocytes.

RESULTS: Compared to the wild-type enzyme, the mutants G900R and E902K showed no significant differences in the voltage dependence of K⁺-induced currents, and analysis of the transient currents indicated that the extracellular Na⁺ affinity was not affected. Mutant G855R showed no pump activity detectable by TEVC. Also for L994del and Y1009X, pump currents could not be recorded. Analysis of the plasma and total membrane fractions showed that the expressed proteins were not or only minimally targeted to the plasma membrane. Whereas the mutation K1003E had no impact on K⁺ interaction, D999H affected the voltage dependence of K⁺-induced currents. Furthermore, kinetics of the transient currents was altered compared to the wild-type enzyme, and the apparent affinity for extracellular Na⁺ was reduced.

CONCLUSION: The investigated FHM2/SHM mutations influence protein function differently depending on the structural impact of the mutated residue.

Acute encephalopathy in familial hemiplegic migraine with ATP1A2 mutation

Familial hemiplegic migraine is a rare subtype of migraine with aura which includes motor weakness. A 32-year-old woman with known familial hemiplegic migraine (point mutation in Exon 22 of the ATP1A2 gene) presented with an acute confusional state, after an initially typical migraine. On examination, she had fever (38°C), agitated, with a right hemiparesis and dysphasia. Electroencephalography showed slowing of α rhythm and continuous rhythmical δ activity in the left hemisphere. She recovered 48 h after the onset of encephalopathic episode. Electroencephalography after recovery showed resolution of the abnormal slowing of the α waveforms.

Novel mutations affecting the Na, K ATPase alpha model complex neurological diseases and implicate the sodium pump in increased longevity

Mutations affecting the Na⁺, K⁺ ATPase alpha subunit have been implicated in at least two distinct human diseases, rapid-onset dystonia Parkinsonism (RDP), and familial hemiplegic migraine (FHM). Over 40 mutations have been mapped to the human ATP1A2 and ATP1A3 genes and are known to result in RDP, FHM or a variant of FHM with neurological complications. To develop a genetically tractable model system for investigating the role of the Na⁺, K⁺ ATPase in neural pathologies we performed genetic screens in Drosophila melanogaster to isolate loss-of-function alleles affecting the Na⁺, K⁺ ATPase alpha subunit. Flies heterozygous for these mutations all exhibit reduced respiration, consistent with a loss-of-function in the major ATPase. However, these mutations do not affect all functions of the Na⁺, K⁺ ATPase alpha protein since embryos homozygous for these mutations have normal septate junction paracellular barrier function and tracheal morphology. Importantly, all of these mutations cause neurological phenotypes and, akin to the mutations that cause RDP and FHM, these new alleles are missense mutations. All of these alleles exhibit progressive stress-induced locomotor impairment suggesting neuromuscular dysfunction, yet neurodegeneration is observed in an allele-specific manner. Surprisingly, studies of longevity demonstrate that mild hypomorphic mutations in the sodium pump significantly improve longevity, which was verified using the Na⁺, K⁺ ATPase antagonist ouabain. The isolation and characterization of a series of new missense alleles of ATPalpha in Drosophila provides the foundation for further studies of these neurological diseases and the role of sodium pump impairment in animal longevity.

The structure of the Na+,K+-ATPase and mapping of isoform differences and disease-related mutations

The Na+,K+-ATPase transforms the energy of ATP to the maintenance of steep electrochemical gradients for sodium and potassium across the plasma membrane. This activity is tissue specific, in particular due to variations in the expressions of the alpha subunit isoforms one through four. Several mutations in alpha2 and 3 have been identified that link the specific function of the Na+,K+-ATPase to the pathophysiology of neurological diseases such as rapid-onset dystonia parkinsonism and familial hemiplegic migraine type 2. We show a mapping of the isoform differences and the disease-related mutations on the recently determined crystal structure of the pig renal Na+,K+-ATPase and a structural comparison to Ca2+-ATPase. Furthermore, we present new experimental data that address the role of a stretch of three conserved arginines near the C-terminus of the alpha subunit (Arg1003-Arg1005).

Pathways-based analyses of whole-genome association study data in bipolar disorder reveal genes mediating ion channel activity and synaptic neurotransmission

Despite known heritability, the complex genetic architecture of bipolar disorder (likely including trait, locus and allelic heterogeneity, as well as genetic interactions) has confounded genetic discovery for many years. Even modern day whole genome association studies (WGAS) using over half a million common SNPs have implicated only a handful of genes at the genomewide level. Temporally coincident with this series of WGAS, a host of pathways-based analyses (PBAs) have emerged as novel computational approaches in the examination of large-scale datasets, but thus far rarely have been applied to WGAS data in psychiatric disorders. Here, we report a series of PBAs conducted using exploratory visual analysis, an analytic and visualization software tool for examining genomic data, to examine results from the National Institutes of Mental Health and Wellcome-Trust Case Control Consortium WGAS in bipolar disorder. Consistent with a host of prior linkage findings, some candidate gene association studies, and recent WGAS, our strongest findings suggest involvement of ion channel structural and regulatory genes, including voltage-gated ion channels and the broader ion channel group that comprises both voltage- and ligand-gated channels. Moreover, we found only modest overlap in the particular genes driving the significance of these gene sets across the analyses. This observation strongly suggests that variation in ion channel genes, as a class of genes, may contribute to the susceptibility of bipolar disorder and that heterogeneity may figure prominently in the genetic architecture of this susceptibility.