Investigation of the CACNA1A gene as a candidate for typical migraine susceptibility

An elongated tract of polyQ in the carboxyl‑terminus of human α1A calcium channel induces cell apoptosis by nuclear translocation

An aberrant elongated tract of glutamine residues (polyQ) in proteins induces multiple diseases treated in the clinic. In our previous study of progressive myoclonic epilepsy (PME), using whole-exome sequencing, a mutant Cav2.1 protein with an aberrant elongated polyQ tract was identified in PME patients. To investigate the molecular mechanism and cell biology of this aberrant elongated polyQ tract, wild-type Cav2.1 with 13 polyQ repeats (Cav2.1 wt-Q13) and mutant-type Cav2.1 with 26 polyQ repeats (Cav2.1 mt-Q26) were prepared and introduced into human SH-SY5Y neuroblastoma cells. Using a WST-1 assay, it was revealed that Cav2.1 mt-Q26 markedly suppressed the proliferation of the SH-SY5Y cells, a result not observed for the Cav2.1 wt-Q13-transfected cells. It was also revealed that Cav2.1 mt and its truncated molecules suppressed cell proliferation by inducing apoptosis rather than arresting the cell cycle. Further investigations indicated a nuclear translocation phenomenon associated with the Cav2.1 mt molecules. Mechanistically, it was revealed that the Cav2.1 mt molecules activated the Bcl-2/Bax, caspase-3 and poly ADP-ribose polymerase (PARP) apoptotic pathways. The present study may provide new insights for interpreting the pathogenesis of PME and the relationship among polyQ, CACNA1A gene mutations and PME.

Analysis of chromosome 1 microsatellite markers and the FHM2-ATP1A2gene mutations in migraine pedigrees

OBJECTIVES

The aims of the study were: (i) to extend our linkage analysis of chromosome 1q microsatellite markers in predominantly migraine with aura pedigrees and (ii) to test the novel FHM-2 ATP1A2 gene for involvement in these migraine affected pedigrees and a previous pedigree (MF14) showing evidence of linkage of markers to C1q31.

METHODS

A chromosome 1 scan (31 markers) was performed in 21 multiplex pedigrees affected predominantly with migraine with aura (MA). The known FHM-2 ATP1A2 gene mutations were tested, by sequencing, for the involvement in MA and migraine without aura (MO) in these pedigrees. Sequencing was performed in the coding areas of the ATP1A2 gene through three MA individuals from MF14.

RESULTS

Evidence for linkage was obtained at C1q23 to markers spanning the ATP1A2 gene. However, testing of the known ATP1A2 gene mutations (for FHM) in common migraine probands of pedigrees showing excess allele sharing was negative. Sequencing of the entire coding areas of the gene through all the three MA affected from MF14 was also negative for mutations.

DISCUSSION

Microsatellite markers on chromosome 1q23 show evidence of excess allele sharing in MA and some MO pedigrees, suggesting linkage to the common forms of migraine and the presence of a susceptibility gene in this region. The FHM-2 (ATP1A2 gene) does not seem to be involved in the common types of migraine. Despite certain clinical characteristics, the genetic correlation between FHM and familial typical migraine remains unclear. Several candidate genes lie within the C1q23 and C1q31 cytogenetic regions; therefore, further studies are needed.

Progress in genetic studies of pain and analgesia

Interindividual variability in pain sensitivity and the response to analgesic manipulations remains a considerable clinical challenge as well as an area of intense scientific investigation. Techniques in this field have matured rapidly so that much relevant data have emerged only in the past few years. Our increasing understanding of the genetic mediation of these biological phenomena have nonetheless revealed their surprising complexity. This review provides a comprehensive picture and critical analysis of the field and its prospects.

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

OBJECTIVE

We studied a large Irish Caucasian pedigree with familial hemiplegic migraine (FHM) with the aim of finding the causative gene mutation.

BACKGROUND

FHM is a rare autosomal-dominant subtype of migraine with aura, which is linked to 4 loci on chromosomes 19p13, 1q23, 2q24, and 1q31. The mutations responsible for hemiplegic migraine have been described in the CACNA1A gene (chromosome 19p13), ATP1A2 gene (chromosome 1q23), and SCN1A gene (chromosome 2q24).

METHODS

We performed linkage analyses in this family for chromosome 1q23 and performed mutation analysis of the ATP1A2 gene.

RESULTS

Linkage to the FHM2 locus on chromosome 1 was demonstrated. Mutation screening of the ATP1A2 gene revealed a G to C substitution in exon 22 resulting in a novel protein variant, D999H, which co-segregates with FHM within this pedigree and is absent in 50 unaffected individuals. This residue is also highly conserved across species.

CONCLUSIONS

We propose that D999H is a novel FHM ATP1A2 mutation.

Subclinical Impairment of Neuromuscular Transmission in Transient Global Amnesia

OBJECTIVE

To investigate the neuromuscular transmission (NMT) of the patients with transient global amnesia (TGA) using single fiber electromyography (SFEMG).

BACKGROUND

The pathophysiology of TGA remains unknown and several elements support the hypothesis of a shared background with migraine. Recent studies showed that some migraineurs have subclinical abnormalities of NMT by using SFEMG. We aimed to test the patients with TGA using SFEMG.

METHODS

We investigated 6 patients diagnosed with TGA according to published criteria and 5 healthy volunteers with similar ages. SFEMG during voluntary contraction of the extensor digitorum communis muscle, nerve conduction studies and concentric needle electromyography were performed and 20 single fiber potential pairs were recorded from each subject and individual and mean jitter values were calculated.

RESULTS

Three patients with TGA showed pronounced NMT failure by SFEMG, whereas none of the controls disclosed this abnormality. The mean jitter value of TGA patients (35+/-33) was greater than that of the control subjects (25+/-15) (P=0.006). Seventeen of the 120 individual jitter values of the TGA group and only 3 (from 3 different volunteers) of the 100 individual jitter values of the control group exceeded upper normal limit (P=0.004).

CONCLUSIONS

These results suggest that TGA shares the same type of subclinical abnormality of NMT observed in migraine patients in recent studies.

Migraine: a complex genetic disorder

Although family and twin studies show that there is a genetic component to migraine, no genes predisposing to common forms of the disorder have been identified. The most encouraging findings have emerged from the identification of genes causing rare mendelian traits that phenotypically resemble migraine. These studies have pointed migraine research towards ion-transport genes; however, there is no direct evidence of the involvement of these genes in common forms of migraine. Family-based linkage studies have identified several chromosomal regions linked to common forms of migraine, but there is little consistency between studies. The modest success in the identification of contributing gene variants has stimulated research into more effective strategies. These include new phenotyping methods for genetic studies and new study designs-such as case-control and whole-genome association studies-to identify common variants contributing to the trait.

Genetic biomarkers for migraine

Biomarkers are physical signs or laboratory measurements that occur in association with a pathological process and have putative diagnostic and/or prognostic utility. In migraine, clinical, radiological, and biochemical biomarkers might be helpful to improve diagnosis, get insight in pathophysiology, and facilitate treatment choices. Genetic biomarkers are defined as genetic variations (mutations or polymorphisms) that can predict disease susceptibility, disease outcome, or treatment response. As yet, only a few genetic biomarkers for migraine are available. Mutations in 3 different genes responsible for familial hemiplegic migraine, a monogenetic subtype of migraine with aura, and the MTHFR C677T polymorphism in common forms of migraine are clear examples. Many positive findings from linkage studies and association studies in common forms of migraine have not been replicated, and are therefore of less clinical use. In this review, we will discuss genetic biomarkers in migraine.

Migraine with and without aura: association with depression and anxiety disorder in a population-based study. The HUNT Study

Some data indicate that migraine with aura (MA) is more strongly associated with anxiety disorder and depression than migraine without aura (MoA), but the evidence is not conclusive. In the Nord-Trøndelag Health study 1995-1997, a total of 49 205 (75% of the participants) subjects gave valid answers to both HADS (Hospital Anxiety and Depression Scale) and a validated headache questionnaire. Associations between anxiety disorder/depression and MA/MoA were evaluated by multiple logistic regression analysis. Depression (DEP) [odds ratio (OR) 1.7; 95% confidence interval (CI) 1.2, 2.6] and depression with comorbid anxiety disorder (COM) (OR 1.6; 95% CI 1.2, 2.1) were more likely in women having MA than in those with MoA. No stronger association was found for pure anxiety disorder (ANX) in MA vs. MoA (OR 0.9; 95% CI 0.7, 1.5). Among men, we found no difference in prevalence of depression and anxiety disorders between MA and MoA. This is a new finding that might have relevance for both research and clinical treatment.

Genetics of Migraine: An Update

Observations including the long-recognized tendency of migraine to run in families, the high concordance rates for migraine in twins reared together or apart, and the association of specific mutations with a rare migraine form are consistent with a genetic contribution to the disorder. This paper summarizes major findings to date on the genetics of migraine. Study of the heritability of migraine, particularly the common forms of migraine, is beset by several challenges including the absence of easily measurable biological markers, uncertainty about the etiologic and clinical overlap among migraine types, and the apparently complex interplay of environmental and genetic factors in determining migraine phenotype. Nevertheless, significant progress has been realized in recent years. Familial hemiplegic migraine, a rare migraine variant, appears to be transmitted by a Mendelian, autosomal dominant mode of inheritance involving mutations in at least 2 genes. These genes do not seem to be critically involved in the other forms of migraine; however, several other susceptibility loci for more common forms of migraine have been identified in recent genome-wide screens and candidate-locus studies. These and other data suggest that the genetic contribution to migraine is complex, multifactorial, and subject to significant modification by environmental factors.

A novel ATP1A2 mutation in a family with FHM type II

Familial hemiplegic migraine (FHM) is a rare subtype of migraine with aura with an autosomal dominant pattern of inheritance. Six FHM families underwent extensive clinical and genetic investigation. The authors identified a novel ATP1A2 mutation (E700K) in three patients from one family. In the patients, attacks were triggered by several factors including minor head trauma. In one subject a 3-day coma developed after a cerebral angiography. Overall, the phenotype of the patients closely resembles that of previously reported cases of FHM type II. The E700K variant might be regarded as the cause of the disease in this family, but this was not tested functionally.

The CACNA1A and ATP1A2 genes are not involved in dominantly inherited migraine with aura

Epidemiological studies indicate that migraine with typical aura (MA) has a major genetic component but the genes for MA have not been identified. However, the autosomal dominantly inherited familial hemiplegic migraine (FHM) is often caused by mutations in the CACNA1A or ATP1A2 genes. The aim of the study was to investigate if the CACNA1A or ATP1A2 genes are involved in MA with an apparently autosomal dominant mode of inheritance. From a clinic population diagnosed by a trained physician we recruited 34 extended families (comprising 174 MA patients) with an apparently autosomal dominant mode of inheritance of MA. We performed a linkage analysis of 161 of 174 MA patients and 79 unaffected relatives using a framework marker set of 44 markers for chromosome 1 and 22 markers for chromosome 19. Linkage analysis was made with a non-parametric or autosomal dominant parametric model, either allowing for heterogeneity or not, using an affected only analysis. We identified no linkage to CACNA1A and ATP1A2 loci on chromosome 19 or 1, respectively. Additionally, at least two patients from each family and 92 healthy, unrelated controls were selected for a sequence analysis. We sequenced the 48 exons of CACNA1A and the 23 exons of ATP1A2, including promoter and flanking intron sequences. No polymorphism was identified in the CACNA1A or ATP1A2 genes with a strong correlation to MA. Our study shows that the CACNA1A or ATP1A2 genes are probably not involved in MA. To identify the genes involved in the common forms of migraine, future genetic studies should focus on MA and migraine without aura (MO) and not FHM.

No role for estrogen receptor 1 gene intron 1 Pvu II and exon 4 C325G polymorphisms in migraine susceptibility

Background

We have previously reported an association between the estrogen receptor 1 (ESR1) gene exon 8 G594A polymorphism and migraine susceptibility in two independent Australian cohorts. In this paper we report results of analysis of two further single nucleotide polymorphisms (SNPs) in the ESR1 gene in the same study group, the T/C Pvu II SNP in intron 1 and the C325G SNP in exon 4, as well as results of linkage disequilibrium (LD) analysis on these markers.

Methods

We investigated these variants by case-control association analysis in a cohort of 240 migraineurs and 240 matched controls. The SNPs were genotyped using specific restriction enzyme assays. Results were analysed using contingency table methods incorporating the chi-squared statistic. LD results are presented as D' statistics with associated P values.

Results

We found no evidence for association of the Pvu II T/C polymorphism and the C325G polymorphism and migraine susceptibility and no evidence for LD between these two SNPs and the previously implicated exon 8 G594A marker.

Conclusion

We have found no role for the polymorphisms in intron 1 and exon 4 with migraine susceptibility. To further investigate our previously implicated exon 8 marker, we suggest the need for studies with a high density of polymorphisms be undertaken, with particular focus on markers in LD with the exon 8 marker.

No mutations detected in the INSR gene in a chromosome 19p13 linked migraine pedigree

The aim of this study was to investigate through direct sequencing the insulin receptor (INSR) gene in DNA samples from a migraine affected family previously showing linkage to chromosome 19p13 in an attempt to detect disease associated mutations. Migraine is a common debilitating disorder with a significant genetic component. At present, the number and type of genes involved in the common forms of migraine are not clear. The INSR gene on chromosome 19p13.3-13.2 is a gene of interest since a number of single nucleotide polymorphisms (SNPs) located within the gene have been implicated in migraine with (MA) and without aura (MO). Six DNA samples obtained from non-founding migraine affected members of migraine family 1 (MF1) were used in this study. Genomic DNA was sequenced for the INSR gene in exons 1-22 and the promoter region. In the six migraine family member samples, previously reported SNPs were detected within two exonic DNA coding regions of the INSR gene. These SNPs, in exons 13 and 17, do not alter the normal INSR polypeptide sequence. In addition, intron 7 also revealed a DNA base sequence variation. For the 5' untranslated promoter region of the gene, no mutations or polymorphisms were detected. In conclusion, this study detected no INSR mutations in affected members of a chromosome 19 linked migraine pedigree. Hence, migraine linkage to this chromosomal region may involve other candidate genes.

Association analysis of a highly polymorphic CAG Repeat in the human potassium channel gene KCNN3 and migraine susceptibility

BACKGROUND

Migraine is a polygenic multifactorial disease, possessing environmental and genetic causative factors with multiple involved genes. Mutations in various ion channel genes are responsible for a number of neurological disorders. KCNN3 is a neuronal small conductance calcium-activated potassium channel gene that contains two polyglutamine tracts, encoded by polymorphic CAG repeats in the gene. This gene plays a critical role in determining the firing pattern of neurons and acts to regulate intracellular calcium channels.

METHODS

The present association study tested whether length variations in the second (more 3') polymorphic CAG repeat in exon 1 of the KCNN3 gene, are involved in susceptibility to migraine with and without aura (MA and MO). In total 423 DNA samples from unrelated individuals, of which 202 consisted of migraine patients and 221 non-migraine controls, were genotyped and analysed using a fluorescence labelled primer set on an ABI310 Genetic Analyzer. Allele frequencies were calculated from observed genotype counts for the KCNN3 polymorphism. Analysis was performed using standard contingency table analysis, incorporating the chi-squared test of independence and CLUMP analysis.

RESULTS

Overall, there was no convincing evidence that KCNN3 CAG lengths differ between Caucasian migraineurs and controls, with no significant difference in the allelic length distribution of CAG repeats between the population groups (P = 0.090). Also the MA and MO subtypes did not differ significantly between control allelic distributions (P > 0.05). The prevalence of the long CAG repeat (>19 repeats) did not reach statistical significance in migraineurs (P = 0.15), nor was there a significant difference between the MA and MO subgroups observed compared to controls (P = 0.46 and P = 0.09, respectively), or between MA vs MO (P = 0.40).

CONCLUSION

This association study provides no evidence that length variations of the second polyglutamine array in the N-terminus of the KCNN3 channel exert an effect in the pathogenesis of migraine.

Investigation of hormone receptor genes in migraine

Migraine is a common neurological condition with a complex mode of inheritance. Steroid hormones have long been implicated in migraine, although their role remains unclear. Our investigation considered that genes involved in hormonal pathways may play a role in migraine susceptibility. We therefore investigated the androgen receptor (AR) CAG repeat, and the progesterone receptor (PR) PROGINS insert by cross-sectional association analysis. The results showed no association with the AR CAG repeat in our study group of 275 migraineurs and 275 unrelated controls. Results of the PR PROGINS analysis showed a significant difference in the same cohort, and in an independent follow-up study population of 300 migraineurs and 300 unrelated controls. Analysis of the genotypic risk groups of both populations together indicated that individuals who carried the PROGINS insert were 1.8 times more likely to suffer migraine. Interaction analysis of the PROGINS variant with our previously reported associated ESR1 594A variant showed that individuals who possessed at least one copy of both risk alleles were 3.2 times more likely to suffer migraine. Hence, variants of these steroid hormone receptor genes appear to act synergistically to increase the risk of migraine by a factor of three.

Chromosome 19p13 loci in Finnish migraine with aura families

Chromosomal area 19p13 contains two migraine associated genes: a Ca(v)2.1 (P/Q-type) calcium channel alpha(1) subunit gene, CACNA1A, and an insulin receptor gene, INSR. Missense mutations in CACNA1A cause a rare Mendelian form of migraine, familial hemiplegic migraine type 1 (FHM1). Contribution of CACNA1A locus has also been studied in the common forms of migraine, migraine with (MA) and without aura (MO), but the results have been contradictory. The role of INSR is less well established: A region on 19p13 separate from CACNA1A was recently reported to be a major locus for migraine and subsequently, the INSR gene was associated with MA and MO. Our aim was to clarify the role of these loci in MA families by analyzing 72 multigenerational Finnish MA families, the largest family sample so far. We hypothesized that the potential major contribution of the 19p13 loci should be detected in a family sample of this size, and this was confirmed by simulations. We genotyped eight polymorphic microsatellite markers surrounding the INSR and CACNA1A genes on 757 individuals. Using parametric and non-parametric linkage analysis, none of the studied markers showed any evidence of linkage to MA either under locus homogeneity or heterogeneity. However, marginally positive lod scores were observed in three families, and thus for these families the results remain inconclusive. The overall conclusion is that our study did not provide evidence of a major MA susceptibility region on 19p13 and thus we were not able to replicate the INSR locus finding.

Investigation of the low-density lipoprotein receptor gene and cholesterol as a risk factor for migraine

The Low-Density Lipoprotein Receptor (LDLR) gene is a cell surface receptor that plays an important role in cholesterol homeostasis. We investigated the (TA)n polymorphism in exon 18 of the LDLR gene on chromosome 19p13.2 performing an association analysis in 244 typical migraine-affected patients, 151 suffering from migraine with aura (MA), 96 with migraine without aura (MO) and 244 unaffected controls. The populations consisted of Caucasians only, and controls were age- and sex-matched. The results showed no significant difference between groups for allele frequency distributions of the (TA)n polymorphism even after separation of the migraine-affected individuals into subgroups of MA and MO affected patients. This is in contradiction to Mochi et al. who found a positive association of this variant with MO. Our study discusses possible differences between the two studies and extends this research by investigating circulating cholesterol levels in a migraine-affected population.

Migraine genetics

The genetics of migraine is a fascinating and moving research area. Familial hemiplegic migraine, a rare subtype of migraine with a Mendelian pattern of inheritance, is caused by mutations in the chromosome 19 CACNA1A gene in approximately 75% of the families. The finding of mutations in an ionchannel subunit defines migraine as a channelopathy (eg, epilepsy). The genetics of the more frequent variants, migraine with and without aura, is more complex. Several loci have been studied in families and case-control studies, but need to be confirmed.

Acetazolamide acts on neuromuscular transmission abnormalities found in some migraineurs

Mild subclinical impairment of neuromuscular transmission can be detected with single-fibre electromyography (SFEMG) in subgroups of patients suffering from migraine and could be due to dysfunctioning Ca2+-channels on motor axons controlling stimulation-induced acetylcholine release. Acetazolamide, which is thought to ameliorate ion channel function, was shown effective in familial hemiplegic migraine and episodic ataxia type 2, both of which are associated with mutations of the neuronal Ca2+-channel gene CACNA1A, as well as in aura status. We treated therefore in an open pilot study five non-hemiplegic migraineurs showing mild SFEMG abnormalities with acetazolamide for several weeks. This was followed by a normalization of SFEMG recordings in all patients and by clinical improvement in four. These results support the assumption that the subclinical impairment of neuromuscular transmission found in certain migraineurs might be due to dysfunctioning Ca2+-channels.

Absence of known familial hemiplegic migraine (FHM) mutations in the CACNA1A gene in patients with common migraine: implications for genetic testing

Mutations in the gene CACNA1A have been known to cause familial hemiplegic migraine (FHM); it has been suggested, based on indirect genetic studies, that this gene may also be involved in common forms of migraine. To obtain data from direct gene analysis to test this hypothesis, we investigated 143 patients with common migraine, irrespective of their family history, for the presence of mutations known to result in the FHM phenotype; the mutations V714A, R192Q, R583Q, T666M, V1457L, and 11811L were absent in our patient sample. Furthermore, exons 4, 16, 17, and 36 were completely screened by single-strand conformation polymorphism (SSCP), and no other, hitherto unknown, mutations were detected. Bearing in mind that, in particular, the T666M mutation contributes to a large proportion of FHM linked to chromosome 19, we conclude that common migraine is distinct from FHM in its molecular basis and, therefore, most likely also in its pathophysiology. The possibility, however, of the existence of allelic disorders, with mutations located in other regions of the CACNA1A gene, cannot be ruled out. Molecular testing, therefore, is at present not a feasible option for the diagnosis and classification of migraine.

Molecular Mechanisms of Migraine

Migraine is a common complex disorder that affects a large portion of the population and thus incurs a substantial economic burden on society. The disorder is characterized by recurrent headaches that are unilateral and usually accompanied by nausea, vomiting, photophobia, and phonophobia. The range of clinical characteristics is broad and there is evidence of comorbidity with other neurological diseases, complicating both the diagnosis and management of the disorder. Although the class of drugs known as the triptans (serotonin 5-HT(1B/1D) agonists) has been shown to be effective in treating a significant number of patients with migraine, treatment may in the future be further enhanced by identifying drugs that selectively target molecular mechanisms causing susceptibility to the disease.Genetically, migraine is a complex familial disorder in which the severity and susceptibility of individuals is most likely governed by several genes that may be different among families. Identification of the genomic variants involved in genetic predisposition to migraine should facilitate the development of more effective diagnostic and therapeutic applications. Genetic profiling, combined with our knowledge of therapeutic response to drugs, should enable the development of specific, individually-tailored treatment.

Therapies in development for the treatment of migraine

While oral formulations of agonists at the serotonin (5-HT) receptor subdivisions 5-HT(1B/1D)--the "triptan" class of drugs--dominate the market for migraine therapy and while still more triptans are under development, recent research efforts have also explored other pharmacological avenues, which are mostly based on our extended insights into the neuropathology and genetics of migraine. Genetic research, in particular, continues to reveal new potential drug targets, indicating that the migraine treatment options that may become available by 2010 might be substantially different from today's scenery. Meanwhile, pharmaceutical companies make increasing use of drug delivery and formulation technologies to improve the action profile and convenience of use for current triptans and this has even led to a partial revival of "old" migraine drugs, such as ergot alkaloids. The broadest potential, however, lies in a better understanding of the molecular pharmacology of migraine.

The genetics of migraine

The search for genes involved in the pathophysiology of migraine poses major difficulties. First, there is no objective diagnostic method to assess the status of the individuals studied. Second, migraine is a polygenic multifactorial disorder. Familial hemiplegic migraine (FHM) is the only known autosomal dominant subtype of migraine. In half the families with FHM who have been studied, there are mutations in the calcium-channel gene CACNA1A, located on chromosome 19. In other families, a locus has been mapped on chromosome 1. The role of these loci in typical migraine is still unknown. A susceptibility locus for migraine with aura has been located on chromosome 19 (but is distinct from CACNA1A) and a genome-wide linkage analysis has mapped a susceptibility locus on chromosome 4. Another locus for migraine may be on the X chromosome. Finally, many positive association studies have been published, but few have been replicated.

Calcium channel mutations and migraine

An increasing number of mutations in the CACNA1A gene have been identified, which are associated with a broad clinical spectrum, including familial hemiplegic migraine. Transfection studies and mouse model analyses are currently being undertaken to study the correlation between CACNA1A mutations and disease.