Genetic and Phenotypic Profiling of Triptan Users in a Swedish Cluster Headache Cohort.

Up to 25% of individuals who live with cluster headache (CH), an extremely painful primary headache disorder, do not adequately respond to the first-line treatment, triptans. Studies have indicated that genetic variants can play a role in treatment response. Likewise, differences in clinical characteristics can give clues to mechanisms underlying triptan non-response. Our aim was to investigate five genetic variants previously implicated in triptan response and their relation to triptan usage in our Swedish CH cohort and to investigate potential distinctions in clinical characteristics. 545 CH patients were screened for the genetic variants rs1024905, rs6724624, rs4795541, rs5443, and rs2651899 with a case control design based on triptan usage. Analysis of clinical characteristics was based on self-reported questionnaire data from 893 patients. One genetic variant, rs1024905, was significantly associated with triptan non-usage in CH (Pc = 0.010). In addition, multi-allele effector analysis showed that individuals with a higher number of effector variants were less likely to use triptans (P = 0.007). Analysis of clinical characteristics showed that triptan users were more likely to have alcohol as a trigger (57.4% vs 43.4%, P = 0.002), have autonomic symptoms (95.1% vs 88.1%, P = 0.002), and be current smokers (27.0% vs 21.9%, P = 0.033) compared to non-users. These results support the hypothesis that genetic variants can play a role in triptan usage in CH and that patients with a typical CH phenotype are more likely to use triptans.

Use of Prescribed and Non-Prescribed Treatments for Cluster Headache in a Swedish Cohort.

BACKGROUND: Cluster headache (CH) is a debilitating condition, but current therapies leave CH patients in pain. The extent of this problem in Sweden is unknown. METHODS: An anonymized questionnaire was sent to 479 Swedish CH patients to investigate patterns and perceived effects of treatments. RESULTS: Three hundred fourteen answers were analyzed. The population was representative regarding age of onset and sex. Less than half (46%) were satisfied with their abortive treatments, 19% terminated functioning abortive treatments due to side effects. Additionally, 17% of chronic CH patients had not tried the first-line preventive drug verapamil. A small subset had tried illicit substances to treat their CH (0-8% depending on substance). Notably, psilocybin was reported effective as an abortive treatment by 100% (n = 8), and with some level of effect as a preventive treatment by 92% (n = 12). For verapamil, some level of preventive effect was reported among 68% (n = 85). CONCLUSIONS: Our descriptive data illustrate that many Swedish CH patients are undertreated, lack functional therapies, and experience side effects. Further studies are warranted to search for new treatment strategies as well as a revision of current treatment guidelines with the aim of reducing patient disease burden to the greatest extent possible.

Patients with cluster headache show signs of insomnia and sleep related stress: results from an actigraphy and self-assessed sleep study.

BACKGROUND: Cluster headache (CH) is a primary headache disorder which is characterized by circadian timing of headache attacks, usually at nighttime, in around two thirds of patients. Patients with CH often report sleep difficulties, though it is unknown whether this is a cause or a consequence of nightly headache attacks. OBJECTIVE: In this case-control study we have assessed sleep quality in study participants with CH in cluster bout respectively in remission, compared to a control group of neurologically healthy individuals to investigate the potential connection between sleep and CH. METHODS: Fifty study participants with CH and 42 controls were recruited for sleep assessment. Sleep was recorded using MotionWatch 8 actigraphs (CamNTech) for a period of two weeks. Study participants were instructed to wear the unit during rest and sleep and to fill out a sleep diary daily through the two-weeks period. RESULTS: Results from actigraphy recordings and sleep diaries suggested that patients with CH spend longer time in bed than controls (CH 8.1 hours vs. Controls 7.7 hours, p=0.03), but do not sleep more than controls (CH 6.7 hours vs. controls 6.5 hours, p=0.3). In addition, CH patients reported increased sleep latency (p=0.003), particularly during, but not restricted to, cluster bouts. Study participants with CH further reported higher levels of stress at bedtime (p=0.01), and they felt less well rested than controls (p=0.001). CONCLUSION: Our analysis suggests that sleep is negatively affected in CH both in cluster bout and in remission, manifesting in symptoms consistent with insomnia such as prolonged sleep latency and increased time in bed.

Investigating Vitamin D Receptor Genetic Markers in a Cluster Headache Meta-Analysis.

Patients diagnosed with the primary headache disorder known as cluster headache (CH) commonly report that their headache attacks occur in patterns of both circadian and seasonal rhythmicity. Vitamin D is essential for a variety of bodily functions and vitamin D levels are largely regulated by daylight exposure in connection with seasonal variation. For this Sweden-based study, the association between CH and three single-nucleotide polymorphisms in the vitamin D receptor gene, rs2228570, rs1544410, and rs731236, were investigated, as well as CH bouts and trigger factors in relation to seasonal and weather changes. Over 600 study participants with CH and 600 controls were genotyped for rs2228570, and genotyping results for rs1544410 and rs731236 were obtained from a previous genome-wide association study. The genotyping results were combined in a meta-analysis, with data from a Greek study. No significant association was found between rs2228570 and CH or the CH subtype in Sweden, nor did the meta-analysis show significant results for any of the three markers. The most common period of the year to experience CH bouts in Sweden was autumn, and conditions linked to weather or weather changes were also identified as potential triggers for CH bouts for a quarter of the responders who reported bout triggers. Though we cannot rule out vitamin D involvement in CH, this study does not indicate any connection between CH and the three vitamin D receptor gene markers.

Sex Differences in Clinical Features, Treatment, and Lifestyle Factors in Patients With Cluster Headache.

BACKGROUND AND OBJECTIVES: Cluster headache is considered a male-dominated disorder, but we have previously suggested that female patients may display a more severe phenotype. Studies on sex differences in cluster headache have been conflicting; therefore, this study, with the largest validated cluster headache material at present, gives more insights into sex-specific characteristics of the disease. The objective of this study was to describe sex differences in patient demographics, clinical phenotype, chronobiology, triggers, treatment, and lifestyle in a Swedish cluster headache population. METHODS: Study participants were identified by screening medical records from 2014 to 2020, requested from hospitals and neurology clinics in Sweden for the ICD-10 code G44.0 for cluster headache. Each study participant answered a detailed questionnaire on clinical information and lifestyle, and all variables were compared with regard to sex. RESULTS: A total of 874 study participants with a verified cluster headache diagnosis were included. Of the participants, 575 (66%) were male and 299 (34%) were female, and biological sex matched self-reported sex for all. Female participants were to a greater extent diagnosed with the chronic cluster headache subtype compared with male participants (18% vs 9%, p = 0.0002). In line with this observation, female participants report longer bouts than male participants (p = 0.003) and used prophylactic treatment more often (60% vs 48%, p = 0.0005). Regarding associated symptoms, female participants experienced ptosis (61% vs 47%, p = 0.0002) and restlessness (54% vs 46%, p = 0.02) more frequently compared with male participants. More female than male study participants had a positive family history of cluster headache (15% vs 7%, p = 0.0002). In addition, female participants reported diurnal rhythmicity of their attacks more often than male participants (74% vs 63%, p = 0.002). Alcohol as a trigger occurred more frequently in male participants (54% vs 48%, p = 0.01), whereas lack of sleep triggering an attack was more common in female participants (31% vs 20%, p = 0.001). DISCUSSION: With this in-depth analysis of a well-characterized cluster headache population, we could demonstrate that there are significant differences between male and female participants with cluster headache, which should be regarded at the time of diagnosis and when choosing treatment options. The data suggest that female patients generally may be more gravely affected by cluster headache than male patients.

PER Gene Family Polymorphisms in Relation to Cluster Headache and Circadian Rhythm in Sweden.

The trigeminal autonomic cephalalgia, cluster headache (CH), is one of the most painful disorders known to man. One of the disorder's most striking features is the reported diurnal rhythmicity of the attacks. For a majority of patients, the headache attacks occur at approximately the same time every day. Genetic variants of genes involved in the circadian rhythm such as Period Circadian Regulator 1, 2, and 3 (PER1, 2 and 3) are hypothesized to have an effect on the rhythmicity of the attacks. Six PER1, 2 and 3 genetic markers; the indel rs57875989 and five single nucleotide polymorphisms (SNPs), rs2735611, rs2304672, rs934945, rs10462020, and rs228697, were genotyped, using TaqMan® or regular polymerase chain reaction (PCR), in a Swedish CH case control material. Logistic regression showed no association between CH and any of the six genetic variants; rs57875989, p = 0.523; rs2735611, p = 0.416; rs2304672, p = 0.732; rs934945, p = 0.907; rs10462020, p = 0.726; and rs228697, p = 0.717. Furthermore, no difference in allele frequency was found for patients reporting diurnal rhythmicity of attacks, nor were any of the variants linked to diurnal preference. The results of this study indicate no involvement of these PER genetic variants in CH or diurnal phenotype in Sweden.

A national Swedish case-control study investigating incidence and factors associated with idiopathic intracranial hypertension.

OBJECTIVE: To study the incidence of idiopathic intracranial hypertension in Sweden and to explore whether previously proposed risk factors are associated with idiopathic intracranial hypertension by investigating the odds of exposure one year prior to diagnosis in patients compared to controls. METHODS: Using Swedish health care registers and validated diagnostic algorithms, idiopathic intracranial hypertension patients diagnosed between 2000-2016 were compared with randomly selected matched controls, five from the general population and five with obesity. RESULTS: We identified 902 idiopathic intracranial hypertension patients and 4510 matched individuals in each control group. Mean incidence among inhabitants ≥18 years of age was 0.71 per 100,000; rising from 0.53 in 2000-2005 to 0.95 in 2012-2016. There were increased odds for idiopathic intracranial hypertension patients compared to general population for exposure to: kidney failure (odds ratio =13.2 (4.1-42.0)), arterial hypertension (odds ratio =17.5 (10.5-29.3)), systemic lupus erythematosus (odds ratio =13.8 (4.3-44.7)), tetracyclines, sulphonamides, lithium, and corticosteroids. In obese controls, odds ratios were also significantly increased for these exposures. Hormonal contraceptive use and exposure to pregnancy did not appear to be associated factors for idiopathic intracranial hypertension development. CONCLUSIONS: The incidence of idiopathic intracranial hypertension in Sweden is lower relative to reports from other countries but is on the rise. This case-control study confirms several previously reported risk factors associated with idiopathic intracranial hypertension.

The molecular clock gene cryptochrome 1 (CRY1) and its role in cluster headache.

BACKGROUND: Cluster headache is a severe primary headache disorder commonly featuring a strikingly distinct circadian attack pattern. Therefore, the circadian system has been suggested to play a crucial role in the pathophysiology of cluster headache. Cryptochromes are key components of the molecular clock generating circadian rhythms and have previously been shown to be associated with several psychiatric disorders, including seasonal affective disorder, bipolar disorder, and depression. METHODS: In this case-control study, we investigated the role of cryptochrome (CRY) genes in cluster headache by screening 628 cluster headache patients and 681 controls from Sweden for four known genetic variants in the CRY1 (rs2287161 and rs8192440) and CRY2 (rs10838524 and rs1554338) genes. In addition, we analyzed CRY1 gene expression in primary fibroblast cell lines from eleven patients and ten controls. RESULTS: The exonic CRY1 variant rs8192440 was associated with cluster headache on allelic level (p=0.02) and this association was even more pronounced in a subgroup of patients with reported diurnal rhythmicity of attacks (p=0.002). We found a small significant difference in CRY1 gene expression between cluster headache patients and control individuals (p=0.04), but we could not identify an effect of the associated variant rs8192440 on CRY1 expression. CONCLUSIONS: We discovered a disease-associated variant in the CRY1 gene and slightly increased CRY1 gene expression in tissue from cluster headache patients, strengthening the hypothesis of circadian dysregulation in cluster headache. How this gene variant may contribute to the pathophysiology of the disease remains subject to further studies.

Genome-Wide Association Study Identifies Risk Loci for Cluster Headache.

OBJECTIVE: This study was undertaken to identify susceptibility loci for cluster headache and obtain insights into relevant disease pathways. METHODS: We carried out a genome-wide association study, where 852 UK and 591 Swedish cluster headache cases were compared with 5,614 and 1,134 controls, respectively. Following quality control and imputation, single variant association testing was conducted using a logistic mixed model for each cohort. The 2 cohorts were subsequently combined in a merged analysis. Downstream analyses, such as gene-set enrichment, functional variant annotation, prediction and pathway analyses, were performed. RESULTS: Initial independent analysis identified 2 replicable cluster headache susceptibility loci on chromosome 2. A merged analysis identified an additional locus on chromosome 1 and confirmed a locus significant in the UK analysis on chromosome 6, which overlaps with a previously known migraine locus. The lead single nucleotide polymorphisms were rs113658130 (p = 1.92 × 10-17 , odds ratio [OR] = 1.51, 95% confidence interval [CI] = 1.37-1.66) and rs4519530 (p = 6.98 × 10-17 , OR = 1.47, 95% CI = 1.34-1.61) on chromosome 2, rs12121134 on chromosome 1 (p = 1.66 × 10-8 , OR = 1.36, 95% CI = 1.22-1.52), and rs11153082 (p = 1.85 × 10-8 , OR = 1.30, 95% CI = 1.19-1.42) on chromosome 6. Downstream analyses implicated immunological processes in the pathogenesis of cluster headache. INTERPRETATION: We identified and replicated several genome-wide significant associations supporting a genetic predisposition in cluster headache in a genome-wide association study involving 1,443 cases. Replication in larger independent cohorts combined with comprehensive phenotyping, in relation to, for example, treatment response and cluster headache subtypes, could provide unprecedented insights into genotype-phenotype correlations and the pathophysiological pathways underlying cluster headache. ANN NEUROL 2021;90:193-202.

Infectious and inflammatory disorders might increase the risk of developing idiopathic intracranial hypertension - a national case-control study.

OBJECTIVE: To investigate whether conditions causing inflammatory activation are associated with increased risk of idiopathic intracranial hypertension. METHODS: All newly diagnosed idiopathic intracranial hypertension patients (cases) in Sweden between 2000-2016 were identified using pre-determined algorithms (n = 902) and matched with five controls from the general population and five individuals with an obesity diagnosis (n = 4510) for age, sex, region, and vital status. National health registers provided information on infections, inflammatory disorders and dispensed medications. Conditional logistic regression was used to estimate odds ratios and 95% confidence intervals. RESULTS: Compared to general population controls, the cases had fourfold increased odds of having an infection (odds ratio = 4.3, 95% confidence interval 3.3-5.6), and threefold increased odds of an inflammatory disorder the year prior to idiopathic intracranial hypertension diagnosis (odds ratio = 3.2, 95% confidence interval 2.4-4.3). Organ specific analyses showed that odds were increased for the study diseases in the respiratory organ, kidney organ and gastrointestinal tract, but not for female genital infections. Similar results were found when comparing idiopathic intracranial hypertension with obese controls though the odds ratios were of lower magnitude. Sub-analyses on exposure to anti-infectious and anti-inflammatory drugs confirmed the increased odds ratios for idiopathic intracranial hypertension patients. CONCLUSIONS: These findings suggest that major inflammatory activation may be a risk factor in idiopathic intracranial hypertension development.

Analysis of NOS Gene Polymorphisms in Relation to Cluster Headache and Predisposing Factors in Sweden.

Cluster headache is characterized by activation of the autonomic-trigeminal reflex. Nitric oxide can trigger headaches in patients, and nitric oxide signaling is known to be affected in cluster headache. Based on the hypothesis of nitric oxide being involved in cluster headache pathophysiology we investigated nitric oxide synthases as potential candidate genes for cluster headache. We analyzed eight variants in the three forms of nitric oxide synthase (NOS) genes, inducible NOS (iNOS), endothelial NOS (eNOS) and neuronal NOS (nNOS), and tested for association with cluster headache. Swedish cluster headache patients (n = 542) and controls (n = 581) were genotyped using TaqMan® assays on an Applied Biosystems 7500 qPCR cycler. This is the largest performed genetic study on NOS involvement in cluster headache so far. We found an association between cluster headache and one iNOS haplotype consisting of the minor alleles of rs2297518 and rs2779249 (p = 0.022). In addition, one of the analyzed nNOS variants, rs2682826, was associated with reported triptan use (p = 0.039). Our data suggest that genetic variants in NOS genes do not have a strong influence on cluster headache pathophysiology, but that certain combinations of genetic variants in NOS genes may influence the risk of developing the disorder or triptan use.

Anoctamin 3: A Possible Link between Cluster Headache and Ca2+ Signaling.

Cluster headache is a severe primary headache characterized by extremely painful attacks of unilateral headache. Verapamil is commonly used as a prophylactic treatment with good effect. In order to search for new pathways involved in the pathophysiology of cluster headache, we analyzed genetic variants that were previously linked to verapamil response in migraine in a Swedish cluster headache case-control sample. We used TaqMan qPCR for genetic screening and performed a gene expression analysis on associated genes in patient-derived fibroblasts, and further investigated which reference genes were suitable for analysis in fibroblasts from cluster headache patients. We discovered a significant association between anoctamin 3, a gene encoding a calcium-activated ion channel, and cluster headache. The association was not dependent on verapamil treatment since the associated variant, rs1531394, was also overrepresented in patients not using verapamil. No difference was found in the anoctamin 3 gene expression between controls and patients. Also, we determined that TBP, IPO8 and PDHB were suitable reference genes in cluster headache fibroblasts. This finding is the first report of an association between a variant in a gene encoding an ion-channel and cluster headache, and the first significant genetic evidence of calcium involvement in cluster headache pathophysiology.

Analysis of HCRTR2 Gene Variants and Cluster Headache in Sweden.

OBJECTIVE: The purpose of this study was to investigate the HCRTR2 gene variants rs3122156, rs2653342, and rs2653349 in a large homogenous Swedish case-control cohort in order to further evaluate the possible contribution of HCRTR2 to cluster headache. BACKGROUND: Cluster headache is a severe neurovascular disorder and the pathophysiology is not yet fully understood. Due to striking circadian and circannual patterns of this disease, the hypothalamus has been a research focus in cluster headache. Several studies with many different cohorts from Europe have investigated the hypocretin receptor 2 (HCRTR2) gene, which is expressed in the hypothalamus. In particular, one HCRTR2 single nucleotide polymorphism, rs2653349, has been subject to a number of genetic association studies on cluster headache, with conflicting results. Two other HCRTR2 gene variants, rs2653342 and rs2653349, have been reported to be linked to cluster headache in an Italian study. METHODS: We genotyped a total of 517 patients diagnosed with cluster headache and 581 controls, representing a general Swedish population, for rs3122156, rs2653342, and rs2653349 using quantitative real-time PCR. Statistical analyses of genotype, allele, and haplotype frequencies for the 3 gene variants were performed comparing patients and controls. RESULTS: For rs3122156, the minor allele frequency in patients was 25.9% compared to 29.9% in controls (P = .0421). However, this significance did not hold after correction for multiple testing. The minor allele frequencies for rs2653342 (14.7% vs 14.7%) and rs2653349 (19.5% vs 18.8%) were similar for patients and controls. Furthermore, we found one haplotype that was significantly less common in patients than controls (P = .0264). This haplotype included the minor allele for rs3122156 and the major alleles for rs2653342 and rs2653349. Significance did not hold after applying a permutation test. CONCLUSIONS: Our data show a trend for association between cluster headache and the HCRTR2 polymorphism rs3122156, where the minor allele seems to be a protective factor. However, the other 2 HCRTR2 gene variants, including the previously reported rs2653349, were not associated with cluster headache in our Swedish material. A comparison with previous studies points to variance in genotype and allele frequencies among the different populations, which most likely contributes to the opposing results regarding rs2653349. Although the results from this study do not strongly support an association, HCRTR2 remains an interesting candidate gene for involvement in the pathophysiology of cluster headache.

Implications for the migraine SNP rs1835740 in a Swedish cluster headache population.

BACKGROUND: Cluster headache is a severe headache disorder with unknown aetiology. The pathophysiology and symptoms present certain common features with migraine. Specifically, activation of the trigeminal vascular system seems to be involved in both disorders, which is hypothesized to result in neurogenic inflammation and vasodilation of the cerebral vessels. In addition, genetic factors have been implicated in both migraine and cluster headache. OBJECTIVE: In order to determine whether or not migraine and cluster headache share genetic risk factors, we screened two genetic variants known to increase the risk of migraine in Sweden in a Swedish cluster headache case-control study population. METHODS: In all, 541 patients and 581 control subjects were genotyped for rs1835740 in close proximity to MTDH (metadherin) and rs2651899 in the PRDM16 (PR/SET domain 16) gene, using TaqMan® real-time PCR and pyrosequencing. In addition, we analyzed MTDH gene expression in a subset of the material, using reverse transcription real-time PCR to determine relative mRNA levels in primary fibroblast cell lines from patients and controls. RESULTS: We found a trend for association between rs1835740, which is reported to affect MTDH mRNA levels, and cluster headache in our Swedish case-control material (p = 0.043, Χ2 = 4.102). This association was stronger in a subgroup of patients suffering from both cluster headache and migraine (p = 0.031, Χ2 = 6.964). We could further confirm that rs1835740 has an effect on the transcriptional activity of MTDH. In this Swedish cluster headache cohort we did not find an association with the rs2651899 variant. CONCLUSIONS: We conclude that rs1835740 is a potential risk factor for cluster headache in Sweden. Our data indicates that rs1835740 and MTDH might be involved in neurovascular headaches in general whilst rs2651899 is specifically related to migraine.

A genetic CLOCK variant associated with cluster headache causing increased mRNA levels.

Background Cluster headache is characterized by recurrent unilateral headache attacks of severe intensity. One of the main features in a majority of patients is a striking rhythmicity of attacks. The CLOCK ( Circadian Locomotor Output Cycles Kaput) gene encodes a transcription factor that serves as a basic driving force for circadian rhythm in humans and is therefore particularly interesting as a candidate gene for cluster headache. Methods We performed an association study on a large Swedish cluster headache case-control sample (449 patients and 677 controls) screening for three single nucleotide polymorphisms (SNPs) in the CLOCK gene implicated in diurnal preference (rs1801260) or sleep duration (rs11932595 and rs12649507), respectively. We further wanted to investigate the effect of identified associated SNPs on CLOCK gene expression. Results We found a significant association with rs12649507 and cluster headache ( p = 0.0069) and this data was strengthened when stratifying for reported diurnal rhythmicity of attacks ( p = 0.0009). We investigated the effect of rs12649507 on CLOCK gene expression in human primary fibroblast cultures and identified a significant increase in CLOCK mRNA expression ( p = 0.0232). Conclusions Our results strengthen the hypothesis of the involvement of circadian rhythm in cluster headache.

Cluster headache - clinical pattern and a new severity scale in a Swedish cohort.

Background The aim of this study was to investigate clinical features of a cluster headache cohort in Sweden and to construct and test a new scale for grading severity. Methods Subjects were identified by screening medical records for the ICD 10 code G44.0, that is, cluster headache. Five hundred participating research subjects filled in a questionnaire including personal, demographic and medical aspects. We constructed a novel scale for grading cluster headache in this cohort: The Cluster Headache Severity Scale, which included number of attacks per day, attack and period duration. The lowest total score was three and the highest 12, and we used the Cluster Headache Severity Scale to grade subjects suffering from cluster headache. We further implemented the scale by defining a cluster headache maximum severity subgroup with a high Cluster Headache Severity Scale score ≥ 9. Results A majority (66.7%) of the patients reported that attacks appear at certain time intervals. In addition, cluster headache patients who were current tobacco users or had a history of tobacco consumption had a later age of disease onset (31.7 years) compared to non-tobacco users (28.5 years). The Cluster Headache Severity Scale score was higher in the patient group reporting sporadic or no alcohol intake than in the groups reporting an alcohol consumption of three to four standard units per week or more. Maximum severity cluster headache patients were characterised by higher age at disease onset, greater use of prophylactic medication, reduced hours of sleep, and lower alcohol consumption compared to the non-cluster headache maximum severity group. Conclusion There was a wide variation of severity grade among cluster headache patients, with a very marked impact on daily living for the most profoundly affected.

Migraine and risk of stroke: a national population-based twin study.

Numerous studies have indicated an increased risk for stroke in patients with migraine, especially migraine with aura; however, many studies used self-reported migraine and only a few controlled for familial factors. We aimed to investigate migraine as a risk factor for stroke in a Swedish population-based twin cohort, and whether familial factors contribute to an increased risk. The study population included twins without prior cerebrovascular disease who answered a headache questionnaire during 1998 and 2002 for twins born 1935-58 and during 2005-06 for twins born between 1959 and 1985. Migraine with and without aura and probable migraine was defined by an algorithm mapping on to clinical diagnostic criteria according to the International Classification of Headache Disorders. Stroke diagnoses were obtained from the national patient and cause of death registers. Twins were followed longitudinally, by linkage of national registers, from date of interview until date of first stroke, death, or end of study on 31 Dec 2014. In total, 8635 twins had any migraineous headache, whereof 3553 had migraine with aura and 5082 had non-aura migraineous headache (including migraine without aura and probable migraine), and 44 769 twins had no migraine. During a mean follow-up time of 11.9 years we observed 1297 incident cases of stroke. The Cox proportional hazards model with attained age as underlying time scale was used to estimate hazard ratios with 95% confidence intervals for stroke including ischaemic and haemorrhagic subtypes related to migraine with aura, non-aura migraineous headache, and any migraineous headache. Analyses were adjusted for gender and cardiovascular risk factors. Where appropriate; within-pair analyses were performed to control for confounding by familial factors. The age- and gender-adjusted hazard ratio for stroke related to migraine with aura was 1.27 (95% confidence interval 1.00-1.62), P = 0.05, and 1.07 (95% confidence interval 0.91-1.26), P = 0.39 related to any migraineous headache. Multivariable adjusted analyses showed similar results. When stratified by gender and attained age of ≤50 or >50 years, the estimated hazard ratio for stroke was higher in twins younger than 50 years and in females; however, non-significant. In the within-pair analysis, the hazard ratio for stroke related to migraine with aura was attenuated [hazard ratio 1.09 (95% confidence interval 0.81-1.46), P = 0.59]. In conclusion, we observed no increased stroke risk related to migraine overall but there was a modestly increased risk for stroke related to migraine with aura, and within-pair analyses suggested that familial factors might contribute to this association.

Screening of genetic variants in ADCYAP1R1, MME and 14q21 in a Swedish cluster headache cohort.

BACKGROUND: We have genotyped a Swedish cluster headache case-control population for three genetic variants representing the most significant markers identified in a recently published genome wide association study on cluster headache. The genetic variants were two common polymorphisms; rs12668955 in ADCYAP1R1 (adenylate cyclase activating polypeptide 1 receptor type 1), rs1006417, an intergenic variant on chromosome 14q21 and one rare mutation, rs147564881, in MME (membrane metalloendopeptidase). RESULTS: We screened 542 cluster headache patients and 581 controls using TaqMan real-time PCR on a 7500 fast cycler, and pyrosequencing on a PSQ 96 System. Statistical analysis for genotype and allele association showed that neither of the two common variants, rs12668955 and rs1006417 were associated with cluster headache. The MME mutation was investigated with pyrosequencing in patients, of whom all were wild type. CONCLUSION: In conclusion rs12668955 and rs1006417 do not impact the risk of developing cluster headache in the Swedish population. Also, rs147564881 does not seem to be enriched within the Swedish cluster headache patient group.

Screening of Two ADH4 Variations in a Swedish Cluster Headache Case-Control Material.

BACKGROUND: Cluster headache (CH) is a severe neurovascular disorder and an increasing amount of evidence points to a genetic contribution to this disease. When CH was first described, it was observed that alcohol may precipitate an attack during the active phase of the disease. The alcohol dehydrogenase 4 (ADH4) gene encodes an enzyme which contributes to the metabolization of alcohol and is, therefore, an interesting candidate gene for CH. Two Italian groups have reported association of the single nucleotide polymorphism (SNP) rs1126671 located in the ADH4 gene with an increased risk of CH in Italy. In addition, one of the groups found an association between the ADH4 SNP rs1800759 and CH. OBJECTIVE: To perform a replication study on the ADH4 SNPs rs1126671 and rs1800759 in a large homogeneous Swedish case-control cohort in order to further investigate the possible contribution of ADH4 to CH. METHODS: A total of 390 unrelated patients diagnosed with CH and 389 controls representing a general Swedish population were recruited to the study. DNA samples from patients and controls were genotyped for the two ADH4 SNPs rs1126671 and rs1800759 using quantitative real-time polymerase chain reaction. Statistical analyses of genotype, allele and haplotype frequencies for the two SNPs were performed and compared between patients and controls. RESULTS: For rs1126671, the minor allele frequency (A allele) was 32.8% (n = 254) in controls compared with 31.9% (n = 249) in CH patients. The minor allele frequency (A allele) of rs1800759 was 42.3% (n = 324) in controls and 41.9% (n = 327) in CH patients. Statistical analysis showed no significant differences in allele as well as in genotype or haplotype frequencies between the patient and control group for either SNP. This was also seen after stratifying the patient group for experiencing alcohol as a trigger factor. CONCLUSIONS: The data did not support an association of the ADH4 SNPs rs1126671 and rs1800759 with CH. A comparison with previous studies revealed variance in genotype, allele, and haplotype frequencies among the different populations which might contribute to the contradictory results. Although a significant association with CH in Swedish case-control group was not found, ADH4 as a candidate gene for CH could not be excluded.