Functional analysis of missense variants in the TRESK (KCNK18) K channel

KCNG4 Genetic Variant Linked to Migraine Prevents Expression of KCNB1

Migraines are a common type of headache affecting around 15% of the population. The signalling pathways leading to migraines have not been fully understood, but neuronal voltage-gated ion channels, such as KCNG4, have been linked to this pathology. KCNG4 (Kv6.4) is a silent member of the superfamily of voltage-gated potassium (Kv) channels, which expresses in heterotetramers with members of the KCNB (Kv2) family. The genetic variant Kv6.4-L360P has previously been linked to migraines, but their mode of action remains unknown. Here, we characterized the molecular characteristics of Kv6.4-L360P when co-expressed with Kv2.1. We found that Kv6.4-L360P almost completely abolishes Kv2 currents, and we propose that this mechanism in the trigeminal system, linked to the initiation of migraine, leads to the pathology.

Current Update on Categorization of Migraine Subtypes on the Basis of Genetic Variation: a Systematic Review

Migraine is a complex neurovascular disorder that is characterized by severe behavioral, sensory, visual, and/or auditory symptoms. It has been labeled as one of the ten most disabling medical illnesses in the world by the World Health Organization (Aagaard et al Sci Transl Med 6(237):237ra65, 2014). According to a recent report by the American Migraine Foundation (Shoulson et al Ann Neurol 25(3):252-9, 1989), around 148 million people in the world currently suffer from migraine. On the basis of presence of aura, migraine is classified into two major subtypes: migraine with aura (Aagaard et al Sci Transl Med 6(237):237ra65, 2014) and migraine without aura. (Aagaard K et al Sci Transl Med 6(237):237ra65, 2014) Many complex genetic mechanisms have been proposed in the pathophysiology of migraine but specific pathways associated with the different subtypes of migraine have not yet been explored. Various approaches including candidate gene association studies (CGAS) and genome-wide association studies (Fan et al Headache: J Head Face Pain 54(4):709-715, 2014). have identified the genetic markers associated with migraine and its subtypes. Several single nucleotide polymorphisms (Kaur et al Egyp J Neurol, Psychiatry Neurosurg 55(1):1-7, 2019) within genes involved in ion homeostasis, solute transport, synaptic transmission, cortical excitability, and vascular function have been associated with the disorder. Currently, the diagnosis of migraine is majorly behavioral with no focus on the genetic markers and thereby the therapeutic intervention specific to subtypes. Therefore, there is a need to explore genetic variants significantly associated with MA and MO as susceptibility markers in the diagnosis and targets for therapeutic interventions in the specific subtypes of migraine. Although the proper characterization of pathways based on different subtypes is yet to be studied, this review aims to make a first attempt to compile the information available on various genetic variants and the molecular mechanisms involved with the development of MA and MO. An attempt has also been made to suggest novel candidate genes based on their function to be explored by future research.

Genetics of migraine: where are we now?

Migraine is a complex brain disorder explained by the interaction of genetic and environmental factors. In monogenic migraines, including familial hemiplegic migraine and migraine with aura associated with hereditary small-vessel disorders, the identified genes code for proteins expressed in neurons, glial cells, or vessels, all of which increase susceptibility to cortical spreading depression. The study of monogenic migraines has shown that the neurovascular unit plays a prominent role in migraine. Genome-wide association studies have identified numerous susceptibility variants that each result in only a small increase in overall migraine risk. The more than 180 known variants belong to several complex networks of "pro-migraine" molecular abnormalities, which are mainly neuronal or vascular. Genetics has also highlighted the importance of shared genetic factors between migraine and its major co-morbidities, including depression and high blood pressure. Further studies are still needed to map all of the susceptibility loci for migraine and then to understand how these genomic variants lead to migraine cell phenotypes.

The holistic approach to the CHRNA7 gene, hsa-miR-3158-5p, and 15q13.3 hotspot CNVs in migraineurs

Migraine is a neurological disease characterized by severe headache attacks. Combinations of different genetic variations such as copy number variation (CNV) in a gene and microRNA (miRNA) expression can provide a holistic approach to the disease as a pathophysiological, diagnostic, and therapeutic target. CNVs, the Cholinergic Receptor Nicotinic Alpha 7 Subunit (CHRNA7) gene, and expression of gene-targeting miRNAs (hsa-miR-548e-5p and hsa-miR-3158-5p) in migraineurs (n = 102; with aura, n = 43; without aura, n = 59) and non-migraines (n = 120) aged 15-60 years, comparative, case-control study was conducted. Genetic markers were compared with biochemical parameters (BMI, WBC, Urea, GFR, ESR, CRP, HBG). All analyzes were performed by quantitative Real-Time PCR (q-PCR) and fold change was calculated with the 2-ΔΔCT method. The diagnostic power of the CHRNA7 gene, CNV, and miRNAs were analyzed with the receiver operating curve (ROC). CHRNA7 gene and hsa-miR-3158-5p are down-regulated in migraineurs and the gene is controlled by this miRNA via CNVs (p < .05). Both deletion and duplication were detected in patients with migraine for CVN numbers (p = .05). The number of CNV deletions was higher than duplications. When CHRNA7-CNV-hsa-miR-3158-5p was modeled together in the ROC analysis, the area under the curve (AUC) was 0.805, and the diagnostic power was "good". In migraineurs, the CHRNA7 gene can be controlled by hsa-miR-3158-5p via CNVs to modulate the mechanism of pain. These three genetic markers have diagnostic potential and may be used in antimigraine treatments.

Study of variants in genes implicated in rare familial migraine syndromes and their association with migraine in 200,000 exome-sequenced UK Biobank participants

BACKGROUND

A number of genes have been implicated in rare familial syndromes which have migraine as part of their phenotype but these genes have not previously been implicated in the common form of migraine.

METHODS

Among exome-sequenced participants in the UK Biobank, we identified 7194 migraine cases with the remaining 193,433 participants classified as controls. We investigated rare variants in 10 genes previously reported to be implicated in conditions with migraine as a prominent part of the phenotype and carried out gene- and variant-based tests for association.

RESULTS

We found no evidence for association of these genes or variants with the common form of migraine seen in our subjects. In particular, a frameshift variant in KCNK18, p.(Phe139Trpfs*24), which had been shown to segregate with migraine with aura in a multiply affected pedigree, was found in 196 (0.10%) controls as well as in 10 (0.14%) cases (χ²  = 0.96, 1 df, p = 0.33).

CONCLUSIONS

Since there is no other reported evidence to implicate KCNK18, we conclude that this gene and its product, TRESK, should no longer be regarded as being involved in migraine aetiology. Overall, we do not find that rare, functional variants in genes previously implicated to be involved in familial syndromes including migraine as part of the phenotype make a contribution to the commoner forms of migraine observed in this population.

Anatomy and Physiology of Headache

Headache disorders can produce recurrent, incapacitating pain. Migraine and cluster headache are notable for their ability to produce significant disability. The anatomy and physiology of headache disorders is fundamental to evolving treatment approaches and research priorities. Key concepts in headache mechanisms include activation and sensitization of trigeminovascular, brainstem, thalamic, and hypothalamic neurons; modulation of cortical brain regions; and activation of descending pain circuits. This review will examine the relevant anatomy of the trigeminal, brainstem, subcortical, and cortical brain regions and concepts related to the pathophysiology of migraine and cluster headache disorders.

The versatile regulation of K2P channels by polyanionic lipids of the phosphoinositide and fatty acid metabolism

Work over the past three decades has greatly advanced our understanding of the regulation of K_ir K⁺ channels by polyanionic lipids of the phosphoinositide (e.g., PIP₂) and fatty acid metabolism (e.g., oleoyl-CoA). However, comparatively little is known regarding the regulation of the K_2P channel family by phosphoinositides and by long-chain fatty acid–CoA esters, such as oleoyl-CoA. We screened 12 mammalian K_2P channels and report effects of polyanionic lipids on all tested channels. We observed activation of members of the TREK, TALK, and THIK subfamilies, with the strongest activation by PIP₂ for TRAAK and the strongest activation by oleoyl-CoA for TALK-2. By contrast, we observed inhibition for members of the TASK and TRESK subfamilies. Our results reveal that TASK-2 channels have both activatory and inhibitory PIP₂ sites with different affinities. Finally, we provided evidence that PIP₂ inhibition of TASK-1 and TASK-3 channels is mediated by closure of the recently identified lower X-gate as critical mutations within the gate (i.e., L244A, R245A) prevent PIP₂-induced inhibition. Our findings establish that K⁺ channels of the K_2P family are highly sensitive to polyanionic lipids, extending our knowledge of the mechanisms of lipid regulation and implicating the metabolism of these lipids as possible effector pathways to regulate K_2P channel activity.

K2P18.1 translates T cell receptor signals into thymic regulatory T cell development

It remains largely unclear how thymocytes translate relative differences in T cell receptor (TCR) signal strength into distinct developmental programs that drive the cell fate decisions towards conventional (Tconv) or regulatory T cells (Treg). Following TCR activation, intracellular calcium (Ca²⁺) is the most important second messenger, for which the potassium channel K_2P18.1 is a relevant regulator. Here, we identify K_2P18.1 as a central translator of the TCR signal into the thymus-derived Treg (tTreg) selection process. TCR signal was coupled to NF-κB-mediated K_2P18.1 upregulation in tTreg progenitors. K_2P18.1 provided the driving force for sustained Ca²⁺ influx that facilitated NF-κB- and NFAT-dependent expression of FoxP3, the master transcription factor for Treg development and function. Loss of K_2P18.1 ion-current function induced a mild lymphoproliferative phenotype in mice, with reduced Treg numbers that led to aggravated experimental autoimmune encephalomyelitis, while a gain-of-function mutation in K_2P18.1 resulted in increased Treg numbers in mice. Our findings in human thymus, recent thymic emigrants and multiple sclerosis patients with a dominant-negative missense K_2P18.1 variant that is associated with poor clinical outcomes indicate that K_2P18.1 also plays a role in human Treg development. Pharmacological modulation of K_2P18.1 specifically modulated Treg numbers in vitro and in vivo. Finally, we identified nitroxoline as a K_2P18.1 activator that led to rapid and reversible Treg increase in patients with urinary tract infections. Conclusively, our findings reveal how K_2P18.1 translates TCR signals into thymic T cell fate decisions and Treg development, and provide a basis for the therapeutic utilization of Treg in several human disorders.

Mini-Review: Two Brothers in Crime - The Interplay of TRESK and TREK in Human Diseases

TWIK-related spinal cord potassium (TRESK) and TWIK-related potassium (TREK) channels are both subfamilies of the two-pore domain potassium (K2P) channel group. Despite major structural, pharmacological, as well as biophysical differences, emerging data suggest that channels of these two subfamilies are functionally more closely related than previously assumed. Recent studies, for instance, indicate an assembling of TRESK and TREK subunits, leading to the formation of heterodimeric channels with different functional properties compared to homodimeric ones. Formation of tandems consisting of TRESK and TREK subunits might thus multiply the functional diversity of both TRESK and TREK activity. Based on the involvement of these channels in the pathophysiology of migraine, we here highlight the role as well as the impact of the interplay of TRESK and TREK subunits in the context of different disease settings. In this regard, we focus on their involvement in migraine and pain syndromes, as well as on their influence on (neuro-)inflammatory processes. Furthermore, we describe the potential implications for innovative therapeutic strategies that take advantage of TRESK and TREK modulation as well as obstacles encountered in the development of therapies related to the aforementioned diseases.

Genome-wide association study on milk production and somatic cell score for Thai dairy cattle using weighted single-step approach with random regression test-day model

Genome-wide association studies are a powerful tool to identify genomic regions and variants associated with phenotypes. However, only limited mutual confirmation from different studies is available. The objectives of this study were to identify genomic regions as well as genes and pathways associated with the first-lactation milk, fat, protein, and total solid yields; fat, protein, and total solid percentage; and somatic cell score (SCS) in a Thai dairy cattle population. Effects of SNPs were estimated by a weighted single-step GWAS, which back-solved the genomic breeding values predicted using single-step genomic BLUP (ssGBLUP) fitting a single-trait random regression test-day model. Genomic regions that explained at least 0.5% of the total genetic variance were selected for further analyses of candidate genes. Despite the small number of genotyped animals, genomic predictions led to an improvement in the accuracy over the traditional BLUP. Genomic predictions using weighted ssGBLUP were slightly better than the ssGBLUP. The genomic regions associated with milk production traits contained 210 candidate genes on 19 chromosomes [Bos taurus autosome (BTA) 1 to 7, 9, 11 to 16, 20 to 21, 26 to 27 and 29], whereas 21 candidate genes on 3 chromosomes (BTA 11, 16, and 21) were associated with SCS. Many genomic regions explained a small fraction of the genetic variance, indicating polygenic inheritance of the studied traits. Several candidate genes coincided with previous reports for milk production traits in Holstein cattle, especially a large region of genes on BTA14. We identified 141 and 5 novel genes related to milk production and SCS, respectively. These novel genes were also found to be functionally related to heat tolerance (e.g., SLC45A2, IRAG1, and LOC101902172), longevity (e.g., SYT10 and LOC101903327), and fertility (e.g., PAG1). These findings may be attributed to indirect selection in our population. Identified biological networks including intracellular cell transportation and protein catabolism implicate milk production, whereas the immunological pathways such as lymphocyte activation are closely related to SCS. Further studies are required to validate our findings before exploiting them in genomic selection.

TREK channel activation suppresses migraine pain phenotype

Activation and sensitization of trigeminal ganglia (TG) sensory neurons, leading to the release of pro-inflammatory peptides such as calcitonin gene-related peptide (CGRP), are likely a key component in migraine-related headache induction. Reducing TG neuron excitability represents therefore an attractive alternative strategy to relieve migraine pain. Here by using pharmacology and genetic invalidation ex vivo and in vivo, we demonstrate that activating TREK1 and TREK2 two-pore-domain potassium (K_2P) channels inhibits TG neuronal firing sufficiently to fully reverse the migraine-like phenotype induced by NO-donors in rodents. Finally, targeting TREK is as efficient as treatment with CGRP antagonists, which represents one of the most effective migraine therapies. Altogether, our results demonstrate that inhibiting TG excitability by pharmacological activation of TREK channels should be considered as an alternative to the current migraine treatment.

Genetics of migraine

Migraine is a complex brain disorder explained by the interaction of genetic and environmental factors. In monogenic migraines, including familial hemiplegic migraine and migraine with aura associated with hereditary small-vessel disorders, the identified genes encode proteins expressed in neurons, astrocytes or vessels, which all increase the susceptibility to cortical spreading depression. Study of monogenic migraines showed that the neurovascular unit plays a prominent role in migraine. Genome-wide association studies have identified multiple susceptibility variants that only cause a small increase of the global migraine risk. The variants belong to several complex networks of "pro-migraine" molecular abnormalities, which are mainly neuronal or vascular. Genetics has also underscored the importance of genetic factors shared between migraine and its major co-morbidities including depression and high blood pressure. Further studies are still needed to map all of the susceptibility loci for migraine and then to understand how these genomic variants lead to migraine cell phenotypes. Thanks to the advent of new technologies such as induced pluripotent stem cells, genetic data will hopefully finally be able to lead to therapeutic progress.

Comparison of K+ Channel Families

K⁺ channels enable potassium to flow across the membrane with great selectivity. There are four K⁺ channel families: voltage-gated K (K_v), calcium-activated (K_Ca), inwardly rectifying K (K_ir), and two-pore domain potassium (K_2P) channels. All four K⁺ channels are formed by subunits assembling into a classic tetrameric (4x1P = 4P for the K_v, K_Ca, and K_ir channels) or tetramer-like (2x2P = 4P for the K_2P channels) architecture. These subunits can either be the same (homomers) or different (heteromers), conferring great diversity to these channels. They share a highly conserved selectivity filter within the pore but show different gating mechanisms adapted for their function. K⁺ channels play essential roles in controlling neuronal excitability by shaping action potentials, influencing the resting membrane potential, and responding to diverse physicochemical stimuli, such as a voltage change (K_v), intracellular calcium oscillations (K_Ca), cellular mediators (K_ir), or temperature (K_2P).

KCNK18 Biallelic Variants Associated with Intellectual Disability and Neurodevelopmental Disorders Alter TRESK Channel Activity

The TWIK-related spinal cord potassium channel (TRESK) is encoded by KCNK18, and variants in this gene have previously been associated with susceptibility to familial migraine with aura (MIM #613656). A single amino acid substitution in the same protein, p.Trp101Arg, has also been associated with intellectual disability (ID), opening the possibility that variants in this gene might be involved in different disorders. Here, we report the identification of KCNK18 biallelic missense variants (p.Tyr163Asp and p.Ser252Leu) in a family characterized by three siblings affected by mild-to-moderate ID, autism spectrum disorder (ASD) and other neurodevelopment-related features. Functional characterization of the variants alone or in combination showed impaired channel activity. Interestingly, Ser252 is an important regulatory site of TRESK, suggesting that alteration of this residue could lead to additive downstream effects. The functional relevance of these mutations and the observed co-segregation in all the affected members of the family expand the clinical variability associated with altered TRESK function and provide further insight into the relationship between altered function of this ion channel and human disease.

Common variants in KCNK5 and FHL5 genes contributed to the susceptibility of migraine without aura in Han Chinese population

A recent genome-wide meta study suggested that rs67338227 in the FHL5 gene and rs10456100 in the KCNK5 gene are associated with migraine from 27 population-based cohorts excluding Chinese population. Given that migraine without aura (MO) is the most common subtype of migraine, our aim was to systematically investigate the relationship of common variants in FHL5 and KCNK5 genes with the susceptibility to MO and provide clues as to the nature of the mechanisms involved in the etiology of migraine. A total of 3306 subjects including 1042 patients with MO and 2264 controls were recruited for the discovery stage, and 2530 individuals including 842 patients with MO and 1688 controls for the replication stage. Twenty-two tag SNPs (7 from FHL5 and 15 from KCNK5) were selected for genotyping. Genetic associations were analyzed at both single-marker and haplotype levels. Potential functional consequences of the significant SNPs were analyzed using gene expression data obtained from the GTEx database. Two SNPs, rs10456100 (KCNK5, P = 9.01 × 10-9) and rs7775721 (FHL5, P = 6.86 × 10-13), were determined to be significantly associated with MO in the discovery sample and were then replicated in another sample. In the combined sample set, the T allele of both SNPs was significantly associated with the increased risk of MO. Significant eQTL signals were identified for both SNP rs10456100 and rs7775721. Our findings suggest that the T allele carriers of SNP rs10456100 and rs7775721 are at increased risk of migraine.

TRESK background potassium channel modifies the TRPV1-mediated nociceptor excitability in sensory neurons

BACKGROUND

TWIK-related spinal cord potassium channel (TRESK) background potassium channels have a key role in controlling resting membrane potential and excitability of sensory neurons. A frameshift mutation leading to complete loss of TRESK function has been identified in members of a family suffering from migraine with aura. In the present study, we examined the role of TRESK channels on nociceptor function in mice.

METHODS

Calcium imaging was used to investigate the role of TRESK channels in the modulation of the response evoked by transient receptor potential vanilloid 1 (TRPV1) receptor stimulation in dorsal root ganglion neurons. Release of calcitonin gene-related peptide from trigeminal afferents and changes in meningeal blood flow were also measured. Experiments were performed on wild-type and TRESK knockout animals.

RESULTS

Inhibition of TRESK increased the TRPV1-mediated calcium signal in dorsal root ganglion neurons and potentiated capsaicin-induced increases in calcitonin gene-related peptide release and meningeal blood flow. Activation of TRESK decreased the capsaicin sensitivity of sensory neurons, leading to an attenuation of capsaicin-induced increase in meningeal blood flow. In TRESK knockout animals, TRPV1-mediated nociceptive reactions were unaffected by pretreatment with TRESK modulators.

CONCLUSIONS

Pharmacological manipulation of TRESK channels influences the TRPV1-mediated functions of nociceptors. Altered TRESK function might contribute to trigeminal nociceptor sensitization in migraine patients.

Exploring the Hereditary Nature of Migraine

Migraine is a common neurological disorder which affects 15-20% of the population; it has a high socioeconomic impact through treatment and loss of productivity. Current forms of diagnosis are primarily clinical and can be difficult owing to comorbidity and symptom overlap with other neurological disorders. As such, there is a need for better diagnostic tools in the form of genetic testing. Migraine is a complex disorder, encompassing various subtypes, and has a large genetic component. Genetic studies conducted on rare monogenic subtypes, including familial hemiplegic migraine, have led to insights into its pathogenesis via identification of causal mutations in three genes (CACNA1A, ATP1A2 and SCN1A) that are involved in transport of ions at synapses and glutamatergic transmission. Study of familial migraine with aura pedigrees has also revealed other causal genes for monogenic forms of migraine. With respect to the more common polygenic form of migraine, large genome-wide association studies have increased our understanding of the genes, pathways and mechanisms involved in susceptibility, which are largely involved in neuronal and vascular functions. Given the preponderance of female migraineurs (3:1), there is evidence to suggest that hormonal or X-linked components can also contribute to migraine, and the role of genetic variants in mitochondrial DNA in migraine has been another avenue of exploration. Epigenetic studies of migraine have shown links between hormonal variation and alterations in DNA methylation and gene expression. While there is an abundance of preliminary studies identifying many potentially causative migraine genes and pathways, more comprehensive genomic and functional analysis to better understand mechanisms may aid in better diagnostic and treatment outcomes.

Migraine and Two-Pore-Domain Potassium Channels

Migraine is a common, disabling neurological disorder with a genetic, environmental, and hormonal component with an annual prevalence estimated at ~15%. It is characterized by attacks of severe, usually unilateral and throbbing headache, and can be accompanied by nausea, vomiting, and photophobia. Migraine is clinically divided into two main subtypes: migraine with aura, when it is preceded by transient neurological disturbances due to cortical spreading depression (CSD), and migraine without aura. Activation and sensitization of trigeminal sensory neurons, leading to the release of pro-inflammatory peptides, is likely a key component in headache pain initiation and transmission in migraine. In the present review, we will focus on the function of two-pore-domain potassium (K_2P) channels, which control trigeminal sensory neuron excitability and their potential interest for developing new drugs to treat migraine.

The Background K+ Channel TRESK in Sensory Physiology and Pain

TRESK belongs to the K_2P family of potassium channels, also known as background or leak potassium channels due to their biophysical properties and their role regulating membrane potential of cells. Several studies to date have highlighted the role of TRESK in regulating the excitability of specific subtypes of sensory neurons. These findings suggest TRESK could be involved in pain sensitivity. Here, we review the different evidence available that involves the channel in pain and sensory perception, from studies knocking out the channel or overexpressing it to identified mutations that link the channel to migraine pain. In addition, the therapeutic possibilities are discussed, as targeting the channel seems an interesting therapeutic approach to reduce nociceptor activation and to decrease pain.

Analysis of Genetic Variants in SCN1A, SCN2A, KCNK18, TRPA1 and STX1A as a Possible Marker of Migraine

Background

Migraine is a polygenetic disease, considered as a channelopathy. The dysregulation of ion functioning due to genetic changes may activate the trigeminovascular system and induce migraine attack both migraine with aura (MA) and without aura (MO).

Objectives

The aim of the study was to analyze the following variants of genes encoding ion channels and associated protein: c.3199G>A SCN1A, c.56G>A SCN2A, c.28A>G and c.328T>C KCNK18, c.3053A>G TRPA1, c.31-1811C>T STX1A in migraine patients.

Patients and Methods

The study included 170 migraine patients and 173 controls. HRMA and Sanger sequencing were used for genotyping. Meta-analysis was performed for c.28A>G, c.328T>C KCNK18, and c.31-1811C>T STX1A.

Results

AA genotype of c.56G>A SCN2A was found only in migraine patients. Patients with c.328T>C KCNK18 mutation had an increased risk of developing migraine before the age of 18. Moreover, individuals with AA/TC haplotype of KCNK18 had higher attack frequency than those with AA/TT (p<0.05). T allele of c.31-1811C>T STX1A was more frequent in MA patients than MO (p<0.05). The c.3053A>G TRPA1 polymorphism was more common in patients with migraine onset before the age of 15 (p<0.05), while c.31-1811C>T STX1A and c.3199G>A SCN1A before the age of 10 (p<0.01). Meta-analysis showed a significant association of c.31-1811C>T STX1A polymorphism with migraine overall (OR=1.22, p=0.0086), MA, and MO. No association was found for c.28A>G KCNK18, c.328T>C KCNK18, and migraine overall.

Conclusion

Changes in genes encoding ion channels or proteins regulating their functioning may increase the risk of migraines and correlate with clinical features of disease, e.g. age of onset and attack frequency.

TRESK and TREK-2 two-pore-domain potassium channel subunits form functional heterodimers in primary somatosensory neurons

Two-pore-domain potassium channels (K_2P) are the major determinants of the background potassium conductance. They play a crucial role in setting the resting membrane potential and regulating cellular excitability. These channels form homodimers; however, a few examples of heterodimerization have also been reported. The K_2P channel subunits TRESK and TREK-2 provide the predominant background potassium current in the primary sensory neurons of the dorsal root and trigeminal ganglia. A recent study has shown that a TRESK mutation causes migraine because it leads to the formation of a dominant negative truncated TRESK fragment. Surprisingly, this fragment can also interact with TREK-2. In this study, we determined the biophysical and pharmacological properties of the TRESK/TREK-2 heterodimer using a covalently linked TRESK/TREK-2 construct to ensure the assembly of the different subunits. The tandem channel has an intermediate single-channel conductance compared with the TRESK and TREK-2 homodimers. Similar conductance values were recorded when TRESK and TREK-2 were coexpressed, demonstrating that the two subunits can spontaneously form functional heterodimers. The TRESK component confers calcineurin-dependent regulation to the heterodimer and gives rise to a pharmacological profile similar to the TRESK homodimer, whereas the presence of the TREK-2 subunit renders the channel sensitive to the selective TREK-2 activator T2A3. In trigeminal primary sensory neurons, we detected single-channel activity with biophysical and pharmacological properties similar to the TRESK/TREK-2 tandem, indicating that WT TRESK and TREK-2 subunits coassemble to form functional heterodimeric channels also in native cells.

Genetics of migraine aura: an update

Migraine is a common brain disorder with a large genetic component. Of the two main migraine types, migraine with aura and migraine without aura, the genetic underpinning in the former is least understood. Given the evidence from epidemiological studies in cohorts and families that the genetic contribution is highest in migraine with aura, this seems paradoxical. Various genetic approaches have been applied to identify genetic factors that confer risk for migraine. Initially, so-called candidate gene associations studies (CGAS) have been performed that test DNA variants in genes prioritized based on presumed a priori knowledge of migraine pathophysiology. More recently, genome-wide association studies (GWAS) tested variants in any gene in an hypothesis-free manner. Whereas GWAS in migraine without aura, or the more general diagnosis migraine have already identified dozens of gene variants, the specific hunt for gene variants in migraine with aura has been disappointing. The only GWAS specifically investigating migraine with aura yielded only one single associated single nucleotide polymorphism (SNP), near MTDH and PGCP, with genome-wide significance. However, interrogation of all genotyped SNPs, so beyond this one significant hit, was more successful and led to the notion that migraine with aura and migraine without aura are genetically more alike than different. Until now, most relevant genetic discoveries related to migraine with aura came from investigating monogenetic syndromes with migraine aura as a prominent phenotype (i.e. FHM, CADASIL and FASPS). This review will highlight the genetic findings relevant to migraine with aura.

Altered functional properties of a missense variant in the TRESK K+ channel (KCNK18) associated with migraine and intellectual disability

Mutations in the KCNK18 gene that encodes the TRESK K2P potassium channel have previously been linked with typical familial migraine with aura. Recently, an atypical clinical case has been reported in which a male individual carrying the p.Trp101Arg (W101R) missense mutation in the KCNK18 gene was diagnosed with intellectual disability and migraine with brainstem aura. Here we report the functional characterization of this new missense variant. This mutation is located in a highly conserved residue close to the selectivity filter, and our results show although these mutant channels retain their K⁺ selectivity and calcineurin-dependent regulation, the variant causes an overall dramatic loss of TRESK channel function as well as an initial dominant-negative effect when co-expressed with wild-type channels in Xenopus laevis oocytes. The dramatic functional consequences of this mutation thereby support a potentially pathogenic role for this variant and provide further insight into the relationship between the structure and function of this ion channel.

A causal role for TRESK loss of function in migraine mechanisms

The two-pore potassium channel, TRESK has been implicated in nociception and pain disorders. We have for the first time investigated TRESK function in human nociceptive neurons using induced pluripotent stem cell-based models. Nociceptors from migraine patients with the F139WfsX2 mutation show loss of functional TRESK at the membrane, with a corresponding significant increase in neuronal excitability. Furthermore, using CRISPR-Cas9 engineering to correct the F139WfsX2 mutation, we show a reversal of the heightened neuronal excitability, linking the phenotype to the mutation. In contrast we find no change in excitability in induced pluripotent stem cell derived nociceptors with the C110R mutation and preserved TRESK current; thereby confirming that only the frameshift mutation is associated with loss of function and a migraine relevant cellular phenotype. We then demonstrate the importance of TRESK to pain states by showing that the TRESK activator, cloxyquin, can reduce the spontaneous firing of nociceptors in an in vitro human pain model. Using the chronic nitroglycerine rodent migraine model, we demonstrate that mice lacking TRESK develop exaggerated nitroglycerine-induced mechanical and thermal hyperalgesia, and furthermore, show that cloxyquin conversely is able to prevent sensitization. Collectively, our findings provide evidence for a role of TRESK in migraine pathogenesis and its suitability as a therapeutic target.

Evolution of acid nociception: ion channels and receptors for detecting acid

Nociceptors, i.e. sensory neurons tuned to detect noxious stimuli, are found in numerous phyla of the Animalia kingdom and are often polymodal, responding to a variety of stimuli, e.g. heat, cold, pressure and chemicals, such as acid. Owing to the ability of protons to have a profound effect on ionic homeostasis and damage macromolecular structures, it is no wonder that the ability to detect acid is conserved across many species. To detect changes in pH, nociceptors are equipped with an assortment of different acid sensors, some of which can detect mild changes in pH, such as the acid-sensing ion channels, proton-sensing G protein-coupled receptors and several two-pore potassium channels, whereas others, such as the transient receptor potential vanilloid 1 ion channel, require larger shifts in pH. This review will discuss the evolution of acid sensation and the different mechanisms by which nociceptors can detect acid. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

A TREK to Translate Genetics to Mechanisms of Migraine

In this issue of Neuron, Royal et al. (2018) find that a mutant form of the TRESK ion channel linked to migraine undergoes alternative translation to produce an inhibitory protein that blocks TREK channels, leading to neuronal hyperexcitability and migraine in rodents.

TRESK K+ Channel Activity Regulates Trigeminal Nociception and Headache

Although TWIK-related spinal cord K⁺ (TRESK) channel is expressed in all primary afferent neurons in trigeminal ganglia (TG) and dorsal root ganglia (DRG), whether TRESK activity regulates trigeminal pain processing is still not established. Dominant-negative TRESK mutations are associated with migraine but not with other types of pain in humans, suggesting that genetic TRESK dysfunction preferentially affects the generation of trigeminal pain, especially headache. Using TRESK global knock-out mice as a model system, we found that loss of TRESK in all TG neurons selectively increased the intrinsic excitability of small-diameter nociceptors, especially those that do not bind to isolectin B4 (IB4^-). Similarly, loss of TRESK resulted in hyper-excitation of the small IB4^- dural afferent neurons but not those that bind to IB4 (IB4⁺). Compared with wild-type littermates, both male and female TRESK knock-out mice exhibited more robust trigeminal nociceptive behaviors, including headache-related behaviors, whereas their body and visceral pain responses were normal. Interestingly, neither the total persistent outward current nor the intrinsic excitability was altered in adult TRESK knock-out DRG neurons, which may explain why genetic TRESK dysfunction is not associated with body and/or visceral pain in humans. We reveal for the first time that, among all primary afferent neurons, TG nociceptors are the most vulnerable to the genetic loss of TRESK. Our findings indicate that endogenous TRESK activity regulates trigeminal nociception, likely through controlling the intrinsic excitability of TG nociceptors. Importantly, we provide evidence that genetic loss of TRESK significantly increases the likelihood of developing headache.

[Two-pore-domain potassium channels and molecular mechanisms underlying migraine]

Migraine is a common, disabling neurological disorder with genetic, environmental and hormonal components and a prevalence estimated at ∼15%. Migraine episodes are notably related, among several factors, to electric hyperexcitability in sensory neurons. Their electrical activity is controlled by ion channels that generate current, specifically by the two-pore-domain potassium, K2P, channels, which inhibit electrical activity. Mutation in the gene encoding TRESK, a K2P channel, causes the formation of TRESK-MT1, the expected non-functional C-terminal truncated TRESK channel, and an additional unexpected protein, TRESK-MT2, which corresponds to a non-functional N-terminal truncated TRESK channel, through a mechanism called frameshift mutation-induced Alternative Translation Initiation (fsATI). TRESK-MT1 is inactive but TRESK-M2 targets two other ion channels, TREK1 and TREK2, inducing a great stimulation of the neuronal electrical activity that may cause migraines. These findings identify TREK1 and TREK2 as potential molecular targets for migraine treatment and suggest that fsATI should be considered as a distinct class of mutations.

Advances in genetics of migraine

Background

Migraine is a complex neurovascular disorder with a strong genetic component. There are rare monogenic forms of migraine, as well as more common polygenic forms; research into the genes involved in both types has provided insights into the many contributing genetic factors. This review summarises advances that have been made in the knowledge and understanding of the genes and genetic variations implicated in migraine etiology.

Findings

Migraine is characterised into two main types, migraine without aura (MO) and migraine with aura (MA). Hemiplegic migraine is a rare monogenic MA subtype caused by mutations in three main genes - CACNA1A, ATP1A2 and SCN1A - which encode ion channel and transport proteins. Functional studies in cellular and animal models show that, in general, mutations result in impaired glutamatergic neurotransmission and cortical hyperexcitability, which make the brain more susceptible to cortical spreading depression, a phenomenon thought to coincide with aura symptoms. Variants in other genes encoding ion channels and solute carriers, or with roles in regulating neurotransmitters at neuronal synapses, or in vascular function, can also cause monogenic migraine, hemiplegic migraine and related disorders with overlapping symptoms. Next-generation sequencing will accelerate the finding of new potentially causal variants and genes, with high-throughput bioinformatics analysis methods and functional analysis pipelines important in prioritising, confirming and understanding the mechanisms of disease-causing variants.

With respect to common migraine forms, large genome-wide association studies (GWAS) have greatly expanded our knowledge of the genes involved, emphasizing the role of both neuronal and vascular pathways. Dissecting the genetic architecture of migraine leads to greater understanding of what underpins relationships between subtypes and comorbid disorders, and may have utility in diagnosis or tailoring treatments. Further work is required to identify causal polymorphisms and the mechanism of their effect, and studies of gene expression and epigenetic factors will help bridge the genetics with migraine pathophysiology.

Conclusions

The complexity of migraine disorders is mirrored by their genetic complexity. A comprehensive knowledge of the genetic factors underpinning migraine will lead to improved understanding of molecular mechanisms and pathogenesis, to enable better diagnosis and treatments for migraine sufferers.

Protein and Chemical Determinants of BL-1249 Action and Selectivity for K2P Channels

K_2P potassium channels generate leak currents that stabilize the resting membrane potential of excitable cells. Various K_2P channels are implicated in pain, ischemia, depression, migraine, and anesthetic responses, making this family an attractive target for small molecule modulator development efforts. BL-1249, a compound from the fenamate class of nonsteroidal anti-inflammatory drugs is known to activate K_2P2.1(TREK-1), the founding member of the thermo- and mechanosensitive TREK subfamily; however, its mechanism of action and effects on other K_2P channels are not well-defined. Here, we demonstrate that BL-1249 extracellular application activates all TREK subfamily members but has no effect on other K_2P subfamilies. Patch clamp experiments demonstrate that, similar to the diverse range of other chemical and physical TREK subfamily gating cues, BL-1249 stimulates the selectivity filter "C-type" gate that controls K_2P function. BL-1249 displays selectivity among the TREK subfamily, activating K_2P2.1(TREK-1) and K_2P10.1(TREK-2) ∼10-fold more potently than K_2P4.1(TRAAK). Investigation of mutants and K_2P2.1(TREK-1)/K_2P4.1(TRAAK) chimeras highlight the key roles of the C-terminal tail in BL-1249 action and identify the M2/M3 transmembrane helix interface as a key site of BL-1249 selectivity. Synthesis and characterization of a set of BL-1249 analogs demonstrates that both the tetrazole and opposing tetralin moieties are critical for function, whereas the conformational mobility between the two ring systems impacts selectivity. Together, our findings underscore the landscape of modes by which small molecules can affect K_2P channels and provide crucial information for the development of better and more selective K_2P modulators of the TREK subfamily.

Migraine-Associated TRESK Mutations Increase Neuronal Excitability through Alternative Translation Initiation and Inhibition of TREK

It is often unclear why some genetic mutations to a given gene contribute to neurological disorders and others do not. For instance, two mutations have previously been found to produce a dominant negative for TRESK, a two-pore-domain K+ channel implicated in migraine: TRESK-MT, a 2-bp frameshift mutation, and TRESK-C110R. Both mutants inhibit TRESK, but only TRESK-MT increases sensory neuron excitability and is linked to migraine. Here, we identify a new mechanism, termed frameshift mutation-induced alternative translation initiation (fsATI), that may explain why only TRESK-MT is associated with migraine. fsATI leads to the production of a second protein fragment, TRESK-MT2, which co-assembles with and inhibits TREK1 and TREK2, two other two-pore-domain K+ channels, to increase trigeminal sensory neuron excitability, leading to a migraine-like phenotype in rodents. These findings identify TREK1 and TREK2 as potential molecular targets in migraine and suggest that fsATI should be considered as a distinct class of mutations.

Two-pore domain potassium channels: emerging targets for novel analgesic drugs: IUPHAR Review 26

Chronic pain is a debilitating and increasingly common medical problem with few effective treatments. In addition to the direct and indirect economic burden of pain syndromes, the concomitant increase in prescriptions for narcotics has contributed to a sharp rise in deaths associated with drug misuse - the 'opioid crisis'. Together, these issues highlight the unmet clinical and social need for a new generation of safe, efficacious analgesics. The detection and transmission of pain stimuli is largely mediated by somatosensory afferent fibres of the dorsal root ganglia. These nociceptive cells express an array of membrane proteins that have received significant attention as attractive targets for new pain medications. Among these, a growing body of evidence supports a role for the two-pore domain potassium (K2P) family of K⁺ channels. Here, we provide a concise review of the K2P channels, their role in pain biology and their potential as targets for novel analgesic agents.

Family studies to find rare high risk variants in migraine

INTRODUCTION

Migraine has long been known as a common complex disease caused by genetic and environmental factors. The pathophysiology and the specific genetic susceptibility are poorly understood. Common variants only explain a small part of the heritability of migraine. It is thought that rare genetic variants with bigger effect size may be involved in the disease. Since migraine has a tendency to cluster in families, a family approach might be the way to find these variants. This is also indicated by identification of migraine-associated loci in classical linkage-analyses in migraine families. A single migraine study using a candidate-gene approach was performed in 2010 identifying a rare mutation in the TRESK potassium channel segregating in a large family with migraine with aura, but this finding has later become questioned. The technologies of next-generation sequencing (NGS) now provides an affordable tool to investigate the genetic variation in the entire exome or genome. The family-based study design using NGS is described in this paper. We also review family studies using NGS that have been successful in finding rare variants in other common complex diseases in order to argue the promising application of a family approach to migraine.

METHOD

PubMed was searched to find studies that looked for rare genetic variants in common complex diseases through a family-based design using NGS, excluding studies looking for de-novo mutations, or using a candidate-gene approach and studies on cancer. All issues from Nature Genetics and PLOS genetics 2014, 2015 and 2016 (UTAI June) were screened for relevant papers. Reference lists from included and other relevant papers were also searched. For the description of the family-based study design using NGS an in-house protocol was used.

RESULTS

Thirty-two successful studies, which covered 16 different common complex diseases, were included in this paper. We also found a single migraine study. Twenty-three studies found one or a few family specific variants (less than five), while other studies found several possible variants. Not all of them were genome wide significant. Four studies performed follow-up analyses in unrelated cases and controls and calculated odds ratios that supported an association between detected variants and risk of disease. Studies of 11 diseases identified rare variants that segregated fully or to a large degree with the disease in the pedigrees.

CONCLUSION

It is possible to find rare high risk variants for common complex diseases through a family-based approach. One study using a family approach and NGS to find rare variants in migraine has already been published but with strong limitations. More studies are under way.

RNA-Seq investigations of human post-mortem trigeminal ganglia

Background The trigeminal ganglion contains neurons that relay sensations of pain, touch, pressure, and many other somatosensory modalities to the central nervous system. The ganglion is also a reservoir for latent herpes virus 1 infection. To gain a better understanding of molecular factors contributing to migraine and headache, transcriptome analyses were performed on postmortem human trigeminal ganglia. Methods RNA-Seq measurements of gene expression were conducted on small sub-regions of 16 human trigeminal ganglia. The samples were also characterized for transcripts derived from viral and microbial genomes. Herpes simplex virus 1 (HSV-1) antibodies in blood were measured using the luciferase immunoprecipitation assay. Results Observed molecular heterogeneity could be explained by sampling of anatomically distinct sub-regions of the excised ganglia consistent with neurally-enriched and non-neural, i.e. Schwann cell, enriched subregions. The levels of HSV-1 transcripts detected in trigeminal ganglia correlated with blood levels of HSV-1 antibodies. Multiple migraine susceptibility genes were strongly expressed in neurally-enriched trigeminal samples, while others were expressed in blood vessels. Conclusions These data provide a comprehensive human trigeminal transcriptome and a framework for evaluation of inhomogeneous post-mortem tissues through extensive quality control and refined downstream analyses for RNA-Seq methodologies. Expression profiling of migraine susceptibility genes identified by genetic association appears to emphasize the blood vessel component of the trigeminovascular system. Other genes displayed enriched expression in the trigeminal compared to dorsal root ganglion, and in-depth transcriptomic analysis of the KCNK18 gene underlying familial migraine shows selective neural expression within two specific populations of ganglionic neurons. These data suggest that expression profiling of migraine-associated genes can extend and amplify the underlying neurobiological insights obtained from genetic association studies.

Pathophysiology of Migraine: A Disorder of Sensory Processing

Plaguing humans for more than two millennia, manifest on every continent studied, and with more than one billion patients having an attack in any year, migraine stands as the sixth most common cause of disability on the planet. The pathophysiology of migraine has emerged from a historical consideration of the "humors" through mid-20th century distraction of the now defunct Vascular Theory to a clear place as a neurological disorder. It could be said there are three questions: why, how, and when? Why: migraine is largely accepted to be an inherited tendency for the brain to lose control of its inputs. How: the now classical trigeminal durovascular afferent pathway has been explored in laboratory and clinic; interrogated with immunohistochemistry to functional brain imaging to offer a roadmap of the attack. When: migraine attacks emerge due to a disorder of brain sensory processing that itself likely cycles, influenced by genetics and the environment. In the first, premonitory, phase that precedes headache, brain stem and diencephalic systems modulating afferent signals, light-photophobia or sound-phonophobia, begin to dysfunction and eventually to evolve to the pain phase and with time the resolution or postdromal phase. Understanding the biology of migraine through careful bench-based research has led to major classes of therapeutics being identified: triptans, serotonin 5-HT1B/1D receptor agonists; gepants, calcitonin gene-related peptide (CGRP) receptor antagonists; ditans, 5-HT1F receptor agonists, CGRP mechanisms monoclonal antibodies; and glurants, mGlu5 modulators; with the promise of more to come. Investment in understanding migraine has been very successful and leaves us at a new dawn, able to transform its impact on a global scale, as well as understand fundamental aspects of human biology.

Genetics of Migraine: Insights into the Molecular Basis of Migraine Disorders

Migraine is a complex, debilitating neurovascular disorder, typically characterized by recurring, incapacitating attacks of severe headache often accompanied by nausea and neurological disturbances. It has a strong genetic basis demonstrated by rare migraine disorders caused by mutations in single genes (monogenic), as well as familial clustering of common migraine which is associated with polymorphisms in many genes (polygenic). Hemiplegic migraine is a dominantly inherited, severe form of migraine with associated motor weakness. Family studies have found that mutations in three different ion channels genes, CACNA1A, ATP1A2, and SCN1A can be causal. Functional studies of these mutations has shown that they can result in defective regulation of glutamatergic neurotransmission and the excitatory/inhibitory balance in the brain, which lowers the threshold for cortical spreading depression, a wave of cortical depolarization thought to be involved in headache initiation mechanisms. Other putative genes for monogenic migraine include KCKN18, PRRT2, and CSNK1D, which can also be involved with other disorders. There are a number of primarily vascular disorders caused by mutations in single genes, which are often accompanied by migraine symptoms. Mutations in NOTCH3 causes cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a hereditary cerebrovascular disease that leads to ischemic strokes and dementia, but in which migraine is often present, sometimes long before the onset of other symptoms. Mutations in the TREX1 and COL4A1 also cause vascular disorders, but often feature migraine. With respect to common polygenic migraine, genome-wide association studies have now identified single nucleotide polymorphisms at 38 loci significantly associated with migraine risk. Functions assigned to the genes in proximity to these loci suggest that both neuronal and vascular pathways also contribute to the pathophysiology of common migraine. Further studies are required to fully understand these findings and translate them into treatment options for migraine patients.

Molecular factors in migraine

Migraine is a common neurological disorder that affects 11% of adults worldwide. This disease most likely has a neurovascular origin. Migraine with aura (MA) and more common form - migraine without aura (MO) - are the two main clinical subtypes of disease. The exact pathomechanism of migraine is still unknown, but it is thought that both genetic and environmental factors are involved in this pathological process. The first genetic studies of migraine were focused on the rare subtype of MA: familial hemiplegic migraine (FHM). The genes analysed in familial and sporadic migraine are: MTHFR, KCNK18, HCRTR1, SLC6A4, STX1A, GRIA1 and GRIA3. It is possible that migraine is a multifactorial disease with polygenic influence.Recent studies have shown that the pathomechanisms of migraine involves both factors responsible for immune response and oxidative stress such as: cytokines, tyrosine metabolism, homocysteine; and factors associated with pain transmission and emotions e.g.: serotonin, hypocretin-1, calcitonin gene-related peptide, glutamate. The correlations between genetic variants of the HCRTR1 gene, the polymorphism 5-HTTLPR and hypocretin-1, and serotonin were observed. It is known that serotonin inhibits the activity of hypocretin neurons and may affect the appearance of the aura during migraine attack.The understanding of the molecular mechanisms of migraine, including genotype-phenotype correlations, may contribute to finding markers important for the diagnosis and treatment of this disease.

Dominant-Negative Effect of a Missense Variant in the TASK-2 (KCNK5) K+ Channel Associated with Balkan Endemic Nephropathy

TASK-2, a member of the Two-Pore Domain (K2P) subfamily of K⁺ channels, is encoded by the KCNK5 gene. The channel is expressed primarily in renal epithelial tissues and a potentially deleterious missense variant in KCNK5 has recently been shown to be prevalent amongst patients predisposed to the development of Balkan Endemic Nephropathy (BEN), a chronic tubulointerstitial renal disease of unknown etiology. In this study we show that this variant (T108P) results in a complete loss of channel function and is associated with a major reduction in TASK-2 channel subunits at the cell surface. Furthermore, these mutant subunits have a suppressive or ‘dominant-negative’ effect on channel function when coexpressed with wild-type subunits. This missense variant is located at the extracellular surface of the M2 transmembrane helix and by using a combination of structural modelling and further functional analysis we also show that this highly-conserved threonine residue is critical for the correct function of other K2P channels. These results therefore provide further structural and functional insights into the possible pathophysiological effects of this missense variant in TASK-2.

Genetic studies of Polish migraine patients: screening for causative mutations in four migraine-associated genes

BACKGROUND AND AIM

Migraine is the most common neurological disorder, affecting approximately 12 % of the adult population worldwide, caused by both environmental and genetic factors. Three causative genes have been identified in familial hemiplegic migraine (FHM) families: CACNA1A, ATP1A2, and SCNA1A. Recently, several mutations in KCNK18 have also been found as causative factors in migraine development. The aim of our study was to identify the genetic background of migraine in the Polish population.

MATERIAL AND METHODS

Sixty patients with migraine without aura (MO) or with different types of migraine with aura (MA), including sporadic hemiplegic, familial hemiplegic, and probable familial hemiplegic, were screened for mutations in the four genes previously linked with different types of migraine (ATP1A2, CACNA1A, SCN1A, and KCNK18).

RESULTS

Two missense mutations were found. One novel mutation in SCN1A, encoding α subunit of sodium channel, causing amino acid change M1500V localized to a region encoding inactivation loop between transmembrane domains III and IV of the channel, was detected in a female FHM patient. The M1500V mutation was absent in a group of 62 controls, as well as in the ExAC database. The second, already known missense mutation S231P in KCNK18 was found in a female MA patient. Additionally, a novel intronic polymorphism possibly affecting alternative splicing of SCN1A, at chr2:16685249, g.77659T>C, and c.4581+32A>G, located between exons 24 and 25, in a region encoding the inactivation loop of the sodium channel was found in a female MO patient. No mutations in ATP1A2 or CACNA1A were found in the study group.

CONCLUSIONS

The presence of SCN1A mutations and absence of mutations in ATP1A2 or CACNA1A suggest that the Polish patients represent FHM type 3. On the other hand, the presence of KCNK18 mutation indicated another FHM subtype. It could be speculated that contrary to other European populations, the genetic basis of migraine in the Polish population involves mutations in genes not included in the study. Next-generation sequencing methods should be implemented to identify other migraine-associated variants.

From migraine genes to mechanisms

Migraine is a common multifactorial episodic brain disorder with strong genetic basis. Monogenic subtypes include rare familial hemiplegic migraine, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, familial advanced sleep-phase syndrome (FASPS), and retinal vasculopathy with cerebral leukodystrophy. Functional studies of disease-causing mutations in cellular and/or transgenic models revealed enhanced (glutamatergic) neurotransmission and abnormal vascular function as key migraine mechanisms. Common forms of migraine (both with and without an aura), instead, are thought to have a polygenic makeup. Genome-wide association studies have already identified over a dozen genes involved in neuronal and vascular mechanisms. Here, we review the current state of molecular genetic research in migraine, also with respect to functional and pathway analyses. We will also discuss how novel experimental approaches for the identification and functional characterization of migraine genes, such as next-generation sequencing, induced pluripotent stem cell, and optogenetic technologies will further our understanding of the molecular pathways involved in migraine pathogenesis.

KCNK18 (TRESK) genetic variants in Italian patients with migraine

OBJECTIVES

To evaluate the prevalence of KCNK18 gene mutations in a dataset of Italian migraineurs, with and without aura, and in healthy controls, and to investigate in silico the functional effects of the mutations.

BACKGROUND

A role for the KCNK18 gene encoding for TRESK, a member of the family of potassium channel, has been recently suggested in migraine with aura.

METHODS

We sequenced the KCNK18 gene in 425 migraineurs (255 with aura and 170 without aura) and 247 healthy controls.

RESULTS

Five genetic variants (R10G, C110R, Y163Y, S231P, and F372L) were found in 13 (5.1%) out of 255 migraine with aura patients, and 6 variants (R10G, D46D, C110R, Y163Y, S178T, and S231P) were identified in 12 (7.1%) out of 170 migraine without aura patients. In 2.8% of controls, the R10G and L20V substitutions were found. In silico analysis suggested that C110R, S178T, S231P, and F372L mutations may have potential damaging effect on channel function, whereas the remaining mutations may have low damaging effect.

CONCLUSIONS

Our study shows the presence of several KCNK18 gene mutations in both migraine with aura and migraine without aura. However, the precise role of this gene in migraine predisposition deserves further studies.

Much more than a leak: structure and function of K₂p-channels

Over the last decade, we have seen an enormous increase in the number of experimental studies on two-pore-domain potassium channels (K2P-channels). The collection of reviews and original articles compiled for this special issue of Pflügers Archiv aims to give an up-to-date summary of what is known about the physiology and pathophysiology of K2P-channels. This introductory overview briefly describes the structure of K2P-channels and their function in different organs. Its main aim is to provide some background information for the 19 reviews and original articles of this special issue of Pflügers Archiv. It is not intended to be a comprehensive review; instead, this introductory overview focuses on some unresolved questions and controversial issues, such as: Do K2P-channels display voltage-dependent gating? Do K2P-channels contribute to the generation of action potentials? What is the functional role of alternative translation initiation? Do K2P-channels have one or two or more gates? We come to the conclusion that we are just beginning to understand the extremely complex regulation of these fascinating channels, which are often inadequately described as 'leak channels'.

Migraine pathophysiology: lessons from mouse models and human genetics

Migraine is a common, disabling, and undertreated episodic brain disorder that is more common in women than in men. Unbiased genome-wide association studies have identified 13 migraine-associated variants pointing at genes that cluster in pathways for glutamatergic neurotransmission, synaptic function, pain sensing, metalloproteinases, and the vasculature. The individual pathogenetic contribution of each gene variant is difficult to assess because of small effect sizes and complex interactions. Six genes with large effect sizes were identified in patients with rare monogenic migraine syndromes, in which hemiplegic migraine and non-hemiplegic migraine with or without aura are part of a wider clinical spectrum. Transgenic mouse models with human monogenic-migraine-syndrome gene mutations showed migraine-like features, increased glutamatergic neurotransmission, cerebral hyperexcitability, and enhanced susceptibility to cortical spreading depression, which is the electrophysiological correlate of aura and a putative trigger for migraine. Enhanced susceptibility to cortical spreading depression increased sensitivity to focal cerebral ischaemia, and blocking of cortical spreading depression improved stroke outcome in these mice. Changes in female hormone levels in these mice modulated cortical spreading depression susceptibility in much the same way that hormonal fluctuations affect migraine activity in patients. These findings confirm the multifactorial basis of migraine and might allow new prophylactic options to be developed, not only for migraine but potentially also for migraine-comorbid disorders such as epilepsy, depression, and stroke.