Combined genotype of HCRTR2 and CLOCK variants in a large family of cluster headache with familial periodicity phenotype

PURPOSE

Cluster headache (CH) is a debilitating condition with severe and recurrent headaches characterized by circannual and circadian rhythms. A genetic contingent was suggested, and several loci were described in large cohorts. However, no variant associated with CH for multiplex families has been described. The purpose of our study was to examine candidate genes and new genetic variants in a multigenerational family of cluster headaches in which two members have original chronobiological characteristics that we have called the phenomenon of "family periodicity".

METHODS AND RESULTS

We performed a whole genome sequencing in four patients in a large multigenerational family of cluster headache to identify additional loci associated with CH. This allowed us to replicate the genomic association of HCRTR2 and CLOCK as candidate genes. In two family members with the same phenotypic circadian pattern (familial periodicity) the association of polymorphism NM_001526.4:c.922G > A was shown in the HCRTR2 gene, and NM_004898.4:c.213T > C in the CLOCK gene.

INTERPRETATION

This whole genome sequencing reproduced two genetic risk loci for CH already involved in its pathogenicity. This is the first time that the combination of HCRTR2 and CLOCK gene variants is identified in a multigenerational family of CH with striking periodicity characteristics. Our study supports the hypothesis that the combination of HCRTR2 and CLOCK gene variants can contribute to the risk of cluster headache and offer the prospect of a new area of research on the molecular circadian clock.

Genetic overlap between temporomandibular disorders and primary headaches: A systematic review

Primary headache disorders (PHD), specifically migraine, are strongly associated with temporomandibular disorders (TMD), sharing some patterns of orofacial pain. Both disorders have significant genetic contributions already studied. PRISMA guidelines were followed to conduct this systematic review, which comprehensively summarize and discuss the genetic overlap between TMD and PHD to aid future research in potential therapy targets. This review included eight original articles published between 2015 and 2020, written in English and related to either TMD and/or PHD. The genes simultaneously assessed in PHD and TMD studies were COMT, MTHFR, and ESR1. COMT was proved to play a critical role in TMD pathogenesis, as all studies have concluded about its impact on the occurrence of the disease, although no association with PHD was found. No proof on the impact of MTHFR gene regulation on either TMD or PHD was found. The most robust results are concerning the ESR1 gene, which is present in the genetic profile of both clinical conditions. This novel systematic review highlights not only the need for a clear understanding of the role of ESR1 and COMT genes in pain pathogenesis, but it also evaluates their potential as a promising therapeutic target to treat both pathologies.

Gene polymorphism association studies in cluster headache: A field synopsis and systematic meta-analyses

BACKGROUND

A plethora of studies have attempted to identify genetic determinants of disease susceptibility and treatment response of patients with cluster headache (CH), but results are often conflicting, and no comprehensive overview with a quantitative summary of the evidence in this field is available.

METHODS

A systematic search of relevant publications was performed without any language restrictions on PubMed, Web of Knowledge, Cochrane Library, and OpenGrey, up to December 2020. A standardized data extraction form was used to collect relevant data from each included study. Meta-analyses were conducted for gene polymorphisms investigated in at least two studies and the Bayesian false discovery probability (BFDP) test was applied to the pooled odds ratios (ORs) to assess the credibility of the observed associations.

RESULTS

Among the 27 articles identified by the systematic review, 17 studies evaluating 12 single nucleotide polymorphisms (SNPs) were included in the quantitative data analysis. The pooled results showed no significant association with CH risk of 10 SNPs, including five SNPs of HCRTR2 (rs2653349, rs2653342, rs3122156, rs10498801, and rs3800539), two SNPs of ADH4 (rs1800759 and rs1126671), CLOCK rs1801260, and two SNPs (rs1006417 and ADCYAP1R1 rs12668955) previously identified by a genome-wide association study (GWAS). Conversely, the pooled results revealed the association of the HCRTR2 rs9357855 A allele with a higher risk of CH (A vs. G, OR: 1.33, 95% CI: 1.04-1.72, p = 0.026), and of GNB3 rs5443 with a higher response rate of patients with CH to triptan drugs (CT+TT vs. CC, OR: 1.96, 95% CI: 1.04-3.72, p = 0.038). However, assuming a prior probability of 0.001, the respective BFDP values being higher than 0.8 (BFDP_rs9357855  = 0.998; BFDP_rs5443  = 0.998) revealed lack of noteworthy results.

CONCLUSIONS

Well-designed GWASs and large replication studies are still needed to identify reliable genetic variants of disease susceptibility and treatment response of patients with CH.

The neurobiology of cluster headache

Cluster headache is a primary headache form occurring in paroxysmal excruciatingly severe unilateral head pain attacks usually grouped in periods lasting 1-2months, the cluster periods. A genetic component is suggested by the familial occurrence of the disease but a genetic linkage is yet to be identified. Contemporary activation of trigeminal and cranial parasympathetic systems-the so-called trigemino-parasympathetic reflex-during the headache attacks seem to cause the pain and accompanying oculo-facial autonomic phenomena respectively. At peripheral level, the increased calcitonin gene related peptide (CGRP) plasma levels suggests trigeminal system activation during cluster headache attacks. The temporal pattern of the disease both in terms of circadian rhythmicity and seasonal recurrence has suggested involvement of the hypothalamic biological clock in the pathophysiology of cluster headache. The posterior hypothalamus was investigate as the cluster generator leading to activation of the trigemino-parasympathetic reflex, but the accumulated experience after 20 years of hypothalamic electrical stimulation to treat the condition indicate that this brain region rather acts as pain modulator. Efficacy of monoclonal antibodies to treat episodic cluster headache points to a key role of CGRP in the pathophysiology of the condition.

Genetic Susceptibility Loci in Genomewide Association Study of Cluster Headache

Objective

Identifying common genetic variants that confer genetic risk for cluster headache.

Methods

We conducted a case–control study in the Dutch Leiden University Cluster headache neuro‐Analysis program (LUCA) study population (n = 840) and unselected controls from the Netherlands Epidemiology of Obesity Study (NEO; n = 1,457). Replication was performed in a Norwegian sample of 144 cases from the Trondheim Cluster headache sample and 1,800 controls from the Nord‐Trøndelag Health Survey (HUNT). Gene set and tissue enrichment analyses, blood cell‐derived RNA‐sequencing of genes around the risk loci and linkage disequilibrium score regression were part of the downstream analyses.

Results

An association was found with cluster headache for 4 independent loci (r² < 0.1) with genomewide significance (p < 5 × 10⁻⁸), rs11579212 (odds ratio [OR] = 1.51, 95% confidence interval [CI] = 1.33–1.72 near RP11‐815 M8.1), rs6541998 (OR = 1.53, 95% CI = 1.37–1.74 near MERTK), rs10184573 (OR = 1.43, 95% CI = 1.26–1.61 near AC093590.1), and rs2499799 (OR = 0.62, 95% CI = 0.54–0.73 near UFL1/FHL5), collectively explaining 7.2% of the variance of cluster headache. SNPs rs11579212, rs10184573, and rs976357, as proxy SNP for rs2499799 (r² = 1.0), replicated in the Norwegian sample (p < 0.05). Gene‐based mapping yielded ASZ1 as possible fifth locus. RNA‐sequencing indicated differential expression of POLR1B and TMEM87B in cluster headache patients.

Interpretation

This genomewide association study (GWAS) identified and replicated genetic risk loci for cluster headache with effect sizes larger than those typically seen in complex genetic disorders. ANN NEUROL 2021;90:203–216

The orexin/hypocretin system in neuropsychiatric disorders: Relation to signs and symptoms

Hypocretin-1 and 2 (or orexin A and B) are neuropeptides exclusively produced by a group of neurons in the lateral and dorsomedial hypothalamus that project throughout the brain. In accordance with this, the two different hypocretin receptors are also found throughout the brain. The hypocretin system is mainly involved in sleep-wake regulation, but also in reward mechanisms, food intake and metabolism, autonomic regulation including thermoregulation, and pain. The disorder most strongly linked to the hypocretin system is the primary sleep disorder narcolepsy type 1 caused by a lack of hypocretin signaling, which is most likely due to an autoimmune process targeting the hypocretin-producing neurons. However, the hypocretin system may also be affected, but to a lesser extent and less specifically, in various other neurological disorders. Examples are neurodegenerative diseases such as Alzheimer's, Huntington's and Parkinson's disease, immune-mediated disorders such as multiple sclerosis, neuromyelitis optica, and anti-Ma2 encephalitis, and genetic disorders such as type 1 diabetus mellitus and Prader-Willi Syndrome. A partial hypocretin deficiency may contribute to the sleep features of these disorders.

Cluster Headache: What's New?

Background

Cluster headache is a highly disabling primary headache disorder which is widely described as the most painful condition a human can experience.

Aim

To provide an overview of the clinical characteristics, epidemiology, risk factors, differential diagnosis, pathophysiology and treatment options of cluster headache, with a focus on recent developments in the field.

Methods

Structured review of the literature on cluster headache.

Results

Cluster headache affects approximately one in 1000 of the population. It is characterised by attacks of severe unilateral head pain associated with ipsilateral cranial autonomic symptoms, and the tendency for attacks to occur with circadian and circannual periodicity. The pathophysiology of cluster headache and other primary headache disorders has recently become better understood and is thought to involve the hypothalamus and trigeminovascular system. There is good quality evidence for acute treatment of attacks with parenteral triptans and high flow oxygen; preventive treatment with verapamil; and transitional treatment with oral corticosteroids or greater occipital nerve injection. New pharmacological and neuromodulation therapies have recently been developed.

Conclusion

Cluster headache causes distinctive symptoms, which once they are recognised can usually be managed with a variety of established treatments. Recent pathophysiological understanding has led to the development of newer pharmacological and neuromodulation therapies, which may soon become established in clinical practice.

Targets for migraine treatment: beyond calcitonin gene-related peptide

PURPOSE OF REVIEW

Despite the development of several medications for the acute and preventive treatment of migraine, there are still many patients in whom lack of efficacy, tolerability, interactions or contraindications make other options necessary. CGRP-based drugs have opened the door to a new era of migraine-targeted treatments. Beyond CGRP, there are other promising targets covered here.

RECENT FINDINGS

For the acute treatment of migraine, 5-HT1F receptor agonists, ditans, are now available. Unlike triptans, 5-HT1B/1D receptor agonists, cardiovascular disease is not a contraindication for the use of ditans. The first study on a monoclonal antibody targeting PAC1 receptor was negative, although this may not be the end for the pituitary adenylate cyclase-activating polypeptide (PACAP) pathway as a target.

SUMMARY

Following positive phase-III clinical trials, lasmiditan is the first ditan to be FDA-approved. PACAP has experimental evidence suggesting a role in migraine pathophysiology. As for CGRP, the presence of PACAP in key migraine structures along with positive provocative tests for both PACAP-38 and PACAP-27 indicate this pathway may still be a pharmacological target. Glutamate-based targets have long been considered in migraine. Two clinical trials with memantine, an NMDA-R antagonist, for the preventive treatment of migraine have now been published. The hypothalamus has also been implicated in migraine pathophysiology: the potential role of orexins in migraine is discussed. Acid-sensing ion channels, as well as amylin-blocking drugs, may also become migraine treatments in the future: more research is warranted.

Family History of Cluster Headache: A Systematic Review

Importance

Genetic and environmental factors are thought to contribute to cluster headache, and cluster headache can affect multiple members of a family. A thorough understanding of its inheritance is critical to understanding the pathogenesis of this debilitating disease.

Objective

To systematically review family history rates and inheritance patterns of cluster headache.

Evidence Review

A systematic review was performed in PubMed, Embase, and Cochrane Library. Search criteria were created by a librarian. Articles published between 1985 and 2016, after the publication date of a large review in 1985, were analyzed independently by 2 neurologists to identify family history rates and pedigrees. Pedigrees were analyzed by a genetic counselor.

Findings

A total of 1995 studies were found (1988 through the search criteria and 7 through other means). Forty articles met inclusion criteria: 22 large cohort studies, 1 twin-based study, and 17 case reports or small case series. Across the 22 large cohort studies, the positive family history rate of cluster headache varied between 0% and 22%, with a median of 8.2%. The largest 5 studies, of 1134, 785, 693, 609, and 500 probands each, had a positive family history in 18.0% (numerator not provided), 5.1% (40 of 785 cases), 10.0% (numerator not provided), 2.0% (12 of 609 cases), and 11.2% (56 of 500 cases), respectively. No meta-analysis was performed, given differences in methodologies. Separately, 1 twin-based study examined 37 twin pairs and reported a concordance rate of 5.4% (2 pairs). Finally, 67 pedigrees were identified. Most pedigrees (46 of 67 [69%]) were consistent with an autosomal dominant pattern, but 19 of 67 (28%) were consistent with an autosomal recessive inheritance pattern; 10 pedigrees of probable or atypical cluster headache were identified, and all were consistent with an autosomal dominant inheritance pattern. The sex ratio for cluster headache in identified pedigrees was 1.39 (103:74) in affected men and boys compared with affected women and girls, which is lower than that of the general cluster headache population.

Conclusions and Relevance

Cluster headache is an inherited disorder in a subset of families and is associated with multiple hereditary patterns. There is an unexpectedly high preponderance of women and girls with familial cluster headache; genetic subanalyses limited to female participants are necessary to further explore this observation, because these data are otherwise masked by the higher numbers of male participants with cluster headache. Overall, this systematic review supports the notion that familial cluster headache is likely the result of multiple susceptibility genes as well as environmental factors.

Current Understanding of the Chronobiology of Cluster Headache and the Role of Sleep in Its Management

Cluster headache is uniquely rhythmic in its occurrence both diurnally and annually. This has implications for the clinical approach to the patient but also for our understanding of the role of central structures in its pathological basis. Many intrinsic and extrinsic factors seem to influence CH rhythmicity, including genetics. The proclivity for attacks to occur at night and the possible association with particular sleep phenomena, including sleep apnea, have motivated a number of studies which has improved our understanding but many questions remain unanswered. The sleep-headache interaction seems to be bidirectional and possibly both direct and indirect. The latter could involve more disperse networks of homeostatic regulation, which may better encompass recent observations. Treatment of the headache patient with concurrent sleep problems can be particularly challenging, especially considering side-effects and interactions of commonly used medications. While current treatment guidelines do not incorporate chronotherapeutic thinking, some evidence may suggest that application of such principles on an individual level may be beneficial.

No Association Between G1246A Polymorphism in HCRTR2 Gene and Risk of Cluster Headache: Evidence From an Updated Meta-Analysis of Observational Studies

Background: The hypocretin receptor 2 (HCRTR2) gene may play a pathological role in cluster headache (CH). However, the conclusions of published reports on the relationship between the G1246A polymorphism (rs2653349) in the HCRTR2 gene and risk of CH remain controversial. This purpose of this article is to comprehensively study the current evidence and assess the association between G1246A polymorphism (rs2653349) in the HCRTR2 gene and risk of CH.

Materials and Methods: Four electronic databases—ISI Web of Science, CNKI, PubMed, and EMBASE—were comprehensively searched on August 2020 to find and pinpoint all observational articles related to this study. The association between G1246A polymorphism in the HCRTR2 gene and risk of CH under five different genetic models was evaluated based on the summary odds ratio and corresponding 95 confidence interval (95% CI). Methodological quality was assessed based on the Newcastle–Ottawa Scale (NOS). To assist the analysis, RevMan 5.3 software was used to perform subgroup and sensitivity analyses. Egger's and Begg's tests were then conducted to evaluate and assess publication bias. Finally, a meta-regression was carried out by residual (restricted) maximum likelihood (REML).

Results: Eight observation studies containing 3,161 healthy controls and 1,964 patients with CH were identified and to be used for the meta-analysis. With methodological quality NOS assessment, the incorporated studies showed an average score of 6.4 stars. The pooled data didn't support the association between G1246A polymorphism in the HCRTR2 gene and CH vulnerability in the overall population (OR: 0.85, 95% CI 0.69, 1.03; p = 0.10). Subgroup analysis by ethnicity showed no significant association between G1246A and CH in either Caucasians (OR: 0.89, 95% CI 0.77, 1.01; p = 0.08) or Asians (OR: 1.65, 95% CI 0.80, 3.41; p = 0.18). The robustness of the conclusion was tested and confirmed with the leave-one-out sensitivity analysis. Meta-regression analysis showed that chronological order of publication appeared to be significantly associated with the heterogeneity (t = 2.47, p = 0.039; residual I² = 0%, adjusted R² = 100%).

Conclusion: Our present study showed that the G1246A polymorphism in the HCRTR2 gene did not appear to be an accomplice and associated with CH predisposition among either the Asian or Caucasian population.

Prevalence of familial cluster headache: a systematic review and meta-analysis

INTRODUCTION

The population rate of familial cluster headache (CH) has been reported to be as high as 20% however this varies considerably across studies. To obtain a true estimate of family history in CH, we conducted a systematic review and meta-analysis of previously published data.

METHODS

Our systematic review involved a search of electronic databases (Medline, EMBASE, PubMed, CINAHL) to identify and appraise studies of interest utilising the PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) guidelines. To further ameliorate the accuracy of our analysis we included an additional unpublished cohort of CH patients recruited at a tertiary referral centre for headache, who underwent detailed family history with diagnostic verification in relatives. Data was extracted and meta-analysis conducted to provide a true estimation of family history.

RESULTS

In total, we identified 7 studies which fulfilled our inclusion criteria. The estimated true prevalence of CH patients with a positive family history was 6.27% (95% CI:4.65-8.40%) with an overall I² of 73%. Fitted models for gender subgroups showed higher estimates 9.26% (95% CI: 6.29-13.43%) in females. However the I² for the female model was 58.42% and significant (p = 0.047).

CONCLUSION

Our findings estimate a rate of family history in CH to be approximately 6.27% (95% CI: 4.65-8.40%). While estimates were larger for female probands, we demonstrated high heterogeneity in this subgroup. These findings further support a genetic role in the aetiology of CH.

Orexin/Hypocretin Type 2 Receptor (HCRTR2) Gene as a Candidate Gene in Sertraline-Associated Insomnia in Depressed Patients

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are considered as first-line drugs for treating depressive disorders. Among the adverse effects reported with sertraline is sleep disturbances; however, the etiology lying beneath is obscure. Orexin, the most recently discovered neurotransmitter, is involved in the sleep cycle. It exerts its physiological actions through orexin or hypocretin type 1 and 2 receptors (HCRTR1 and HCRTR2). Dysfunction of the orexin system contributes to various psychiatric, neurologic and neuropsychiatric disorders. Thus, our study aimed to assess the possible association of genetic variation of HCRTR2 G1246A with hypersomnia reported with sertraline in a group of major depressive disorder (MDD) patients.

PATIENTS AND METHODS

Ninety-six newly diagnosed MDD patients were enrolled in our cohort study. MDD was assessed using DSM-V criteria. Insomnia Severity Index (ISI) was used to assess insomnia at baseline (week 0) and week 4. Blood samples were collected for further genotyping of HCRTR2 G1246A (rs2653349) using polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

A significant association between G1264A polymorphism of HCRTR2 and insomnia was observed. Insomnia with sertraline happens by 2.5-fold (P=0.022; odds ratio (OR)=2.5; 95% confidence interval (CI): 1.1-5.7) in patients having GG genotype. Patients with G allele experience insomnia by 2.1-fold more than A allele carriers (P=0.022; OR=2.1; 95% CI= 1.1-4.0). Subgroup analysis showed a significant association between GG genotype as well as the G allele and insomnia only in female MDD patients (P=0.011; OR=4.0; 95% CI=1.3-12.0 and P=0.033; OR=2.4; 95% CI=1.02-5.7, respectively).

CONCLUSION

In conclusion, the G1246A variant might be a predictor for insomnia in MDD patients treated with sertraline. Our findings support the idea that some variants of the HCRTR might contribute to inter-individual variability in the sleep pattern of patients receiving antidepressants.

Analysis of HCRTR2, GNB3, and ADH4 Gene Polymorphisms in a Southeastern European Caucasian Cluster Headache Population

Studies point to an increased hereditary risk of cluster headache. HCRTR2 gene rs2653349 and ADH4 gene rs1800759 polymorphisms have been associated with cluster headache susceptibility. Also, GNB3 rs5443 polymorphism, associated with increased signal transduction via GPCRs, seems to influence triptan treatment response. DNA from 114 cluster headache patients and 570 non-related controls, representing a general Southeastern European Caucasian (SEC) population, was extracted from buccal swabs and genotyped using real-time PCR. Gene distribution for the rs2653349 was GG = 79.8%, GA = 18.4%, and AA = 1.8% for patients and GG = 79.1%, GA = 19.1%, and AA = 1.8% for controls. The frequency of the mutated A allele was 11.0% for patients and 11.3% for controls. The frequencies for rs5443 were CC = 44.7%, CT = 44.7%, and TT = 10.5% for patients and CC = 43.9%, CT = 42.6%, and TT = 13.5% for controls. The frequency of the mutated T allele was 32.9% for patients and 34.8% for controls. A 2.7-fold more frequent appearance of the mutated T allele was observed in patients with better triptan treatment response, although not statistically significant. For rs1800759, the frequencies were CC = 36.0%, CA = 43.0%, and AA = 21.0% for patients and CC = 34.0%, CA = 50.2%, and AA = 15.8% for controls. The frequency of the mutated A allele was 42.5% and 40.9% for patients and controls, respectively. The mutated T allele of GNB3 rs5443 polymorphism was more prevalent in patients with better triptan treatment response, indicating a possible trend of association between this polymorphism and triptan treatment response in SEC population. According to our observation, no association of HCRTR2 rs2653349 and ADH4 rs1800759 polymorphisms and cluster headache in SEC population could be documented.

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.

The biological clock in cluster headache: A review and hypothesis

Objective

To review and discuss the putative role of light, sleep, and the biological clock in cluster headache.

Discussion

Cluster headache attacks are believed to be modulated in the hypothalamus; moreover, the severe pain and typical autonomic cranial features associated with cluster headache are caused by abnormal activity of the trigeminal-autonomic reflex. The temporal pattern of cluster headache attacks suggests involvement of the biological clock, and the seasonal pattern is influenced by the number of daylight hours. Although sleep is often reported as a trigger for cluster headache attacks, to date no clear correlation has been established between these attacks and sleep stage.

Conclusions

We hypothesize that light, sleep, and the biological clock can change the brain’s state, thereby lowering the threshold for activating the trigeminal-autonomic reflex, resulting in a cluster headache attack. Understanding the mechanisms that contribute to the daily and seasonal fluctuations in cluster headache attacks may provide new therapeutic targets.

Perivascular neurotransmitters: Regulation of cerebral blood flow and role in primary headaches

In order to understand the nature of the relationship between cerebral blood flow (CBF) and primary headaches, we have conducted a literature review with particular emphasis on the role of perivascular neurotransmitters. Primary headaches are in general considered complex polygenic disorders (genetic and environmental influence) with pathophysiological neurovascular alterations. Identified candidate headache genes are associated with neuro- and gliogenesis, vascular development and diseases, and regulation of vascular tone. These findings support a role for the vasculature in primary headache disorders. Moreover, neuronal hyperexcitability and other abnormalities have been observed in primary headaches and related to changes in hemodynamic factors. In particular, this relates to migraine aura and spreading depression. During headache attacks, ganglia such as trigeminal and sphenopalatine (located outside the blood-brain barrier) are variably activated and sensitized which gives rise to vasoactive neurotransmitter release. Sympathetic, parasympathetic and sensory nerves to the cerebral vasculature are activated. During migraine attacks, altered CBF has been observed in brain regions such as the somatosensory cortex, brainstem and thalamus. In regulation of CBF, the individual roles of neurotransmitters are partly known, but much needs to be unraveled with respect to headache disorders.

Genetics of cluster headache

BACKGROUND

Cluster headache is the most severe primary headache disorder. A genetic basis has long been suggested by family and twin studies; however, little is understood about the genetic variants that contribute to cluster headache susceptibility.

METHODS

We conducted a literature search of the MEDLINE database using the PubMed search engine to identify all human genetic studies for cluster headache. In this article we provide a review of those genetic studies, along with an overview of the pathophysiology of cluster headache and a brief review of migraine genetics, which have both been significant drivers of cluster headache candidate gene selection.

RESULTS

The investigation of cluster headache genetic etiology has been dominated by candidate gene studies. Candidate selection has largely been driven by the pathophysiology, such as the striking rhythmic nature of the attacks, which spurred close examination of the circadian rhythm genes CLOCK and HCRTR2. More recently, unbiased genetic approaches such as genome-wide association studies (GWAS) have yielded new genetic avenues of interest including ADCYAP1R1 and MME.

CONCLUSIONS

The majority of candidate genes studied for cluster headache suffer from poor reproducibility. Broader genetic interrogation through larger unbiased GWAS, exome, and whole genome studies may provide more robust candidates, and in turn provide a clearer understanding of the causes of cluster headache.

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.

Update on the pathophysiology of cluster headache: imaging and neuropeptide studies

OBJECTIVE

Cluster headache (CH) is the most severe primary headache condition. Its pathophysiology is multifaceted and incompletely understood. This review brings together the latest neuroimaging and neuropeptide evidence on the pathophysiology of CH.

METHODS

A review of the literature was conducted by searching PubMed and Web of Science. The search was conducted using the following keywords: imaging studies, voxel-based morphometry, diffusion-tensor imaging, diffusion magnetic resonance imaging, tractography, connectivity, cerebral networks, neuromodulation, central modulation, deep brain stimulation, orexin-A, orexin-B, tract-based spatial statistics, single-photon emission computer tomography studies, positron-emission tomography, functional magnetic resonance imaging, magnetic resonance spectroscopy, trigeminovascular system, neuropeptides, calcitonin gene-related peptide, neurokinin A, substance P, nitric oxide synthase, pituitary adenylate cyclase-activating peptide, vasoactive intestinal peptide, neuropeptide Y, acetylcholine, noradrenaline, and ATP. "Cluster headache" was combined with each keyword for more relevant results. All irrelevant and duplicated records were excluded. Search dates were from October 1976 to May 2018.

RESULTS

Neuroimaging studies support the role of the hypothalamus in CH, as well as other brain areas involved in the pain matrix. Activation of the trigeminovascular system and the release of neuropeptides play an important role in CH pathophysiology. Among neuropeptides, calcitonin gene-related peptide, vasoactive intestinal peptide, and pituitary adenylate cyclase-activating peptide have been reported to be reliable biomarkers for CH attacks, though not specific for CH. Several other neuropeptides are involved in trigeminovascular activation, but the current evidence does not qualify them as reliable biomarkers in CH.

CONCLUSION

CH has a complex pathophysiology and the pain mechanism is not completely understood. Recent neuroimaging studies have provided insight into the functional and structural network bases of CH pathophysiology. Although there has been important progress in neuropeptide studies, a specific biomarker for CH is yet to be found.

Signaling transduction regulated by 5-hydroxytryptamine 1A receptor and orexin receptor 2 heterodimers

As G-protein-coupled receptors (GPCRs), 5-hydroxytryptamine 1A receptor (5-HT1AR) and orexin receptor 2 (OX2R) regulate the levels of the cellular downstream molecules. The heterodimers of different GPCRs play important roles in various of neurological diseases. Moreover, 5-HT1AR and OX2R are involved in the pathogenesis of neurological diseases such as depression with deficiency of hippocampus plasticity. However, the direct interaction of the two receptors remains elusive. In the present study, we firstly demonstrated the heterodimer formation of 5-HT1AR and OX2R. Exchange protein directly activated by cAMP (Epac) cAMP bioluminescence resonance energy transfer (BRET) biosensor analysis revealed that the expression levels of cellular cAMP significantly increased in HEK293T cells transfected with the two receptors compared with the 5-HT1AR group. Additionally, the cellular level of calcium was upregulated robustly in HEK293T cells co-transfected with 5-HT1AR and OX2R group after agonist treatment. Furthermore, western blotting data showed that 5-HT1AR and OX2R heterodimer decreased the levels of phosphorylation of extracellular signal-regulated kinase (ERK) and cAMP-response element-binding protein (CREB). These results not only unraveled the formation of 5-HT1AR and OX2R heterodimer but also suggested that the heterodimer affected the downstream signaling pathway, which will provide new insights into the function of the two receptors in the brain.

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.

Migraine and cluster headache - the common link

Although clinically distinguishable, migraine and cluster headache share prominent features such as unilateral pain, common pharmacological triggers such glyceryl trinitrate, histamine, calcitonin gene-related peptide (CGRP) and response to triptans and neuromodulation. Recent data also suggest efficacy of anti CGRP monoclonal antibodies in both migraine and cluster headache. While exact mechanisms behind both disorders remain to be fully understood, the trigeminovascular system represents one possible common pathophysiological pathway and network of both disorders. Here, we review past and current literature shedding light on similarities and differences in phenotype, heritability, pathophysiology, imaging findings and treatment options of migraine and cluster headache. A continued focus on their shared pathophysiological pathways may be important in paving future treatment avenues that could benefit both migraine and cluster headache patients.

Linking Cigarette Smoking/Tobacco Exposure and Cluster Headache: A Pathogenesis Theory

INTRODUCTION

To propose a hypothesis theory to establish a linkage between cigarette smoking and cluster headache pathogenesis.

BACKGROUND

Cluster headache is a primary headache syndrome grouped under the trigeminal autonomic cephalalgias. What distinguishes cluster headache from all other primary headache conditions is its inherent connection to cigarette smoking. It is undeniable that tobacco exposure is in some manner related to cluster headache. The connection to tobacco exposure for cluster headache is so strong that even if an individual sufferer never smoked, then that individual typically had significant secondary smoke exposure as a child from parental smoking behavior and in many instances both scenarios exist. The manner by which cigarette smoking is connected to cluster headache pathogenesis is unknown at present. If this could be determined this may contribute to advancing our understanding of cluster headache pathophysiology.

METHODS/RESULTS

Hypothesis statement.

CONCLUSION

The hypothesis theory will include several principles: (1) the need of double lifetime tobacco exposure, (2) that cadmium is possibly the primary agent in cigarette smoke that leads to hypothalamic-pituitary-gonadal axis toxicity promoting cluster headache, (3) that the estrogenization of the brain and its specific sexually dimorphic nuclei is necessary to develop cluster headache with tobacco exposure, and (4) that the chronic effects of smoking and its toxic metabolites including cadmium and nicotine on the cortex are contributing to the morphometric and orexin alterations that have been previously attributed to the primary headache disorder itself.

Cluster Headache: Epidemiology, Pathophysiology, Clinical Features, and Diagnosis

Cluster headache is a primary headache disorder affecting up to 0.1% of the population. Patients suffer from cluster headache attacks lasting from 15 to 180 min up to 8 times a day. The attacks are characterized by the severe unilateral pain mainly in the first division of the trigeminal nerve, with associated prominent unilateral cranial autonomic symptoms and a sense of agitation and restlessness during the attacks. The male-to-female ratio is approximately 2.5:1. Experimental, clinical, and neuroimaging studies have advanced our understanding of the pathogenesis of cluster headache. The pathophysiology involves activation of the trigeminovascular complex and the trigeminal-autonomic reflex and accounts for the unilateral severe headache, the prominent ipsilateral cranial autonomic symptoms. In addition, the circadian and circannual rhythmicity unique to this condition is postulated to involve the hypothalamus and suprachiasmatic nucleus. Although the clinical features are distinct, it may be misdiagnosed, with patients often presenting to the otolaryngologist or dentist with symptoms. The prognosis of cluster headache remains difficult to predict. Patients with episodic cluster headache can shift to chronic cluster headache and vice versa. Longitudinally, cluster headache tends to remit with age with less frequent bouts and more prolonged periods of remission in between bouts.

Cluster Headache Clinical Phenotypes: Tobacco Nonexposed (Never Smoker and No Parental Secondary Smoke Exposure as a Child) versus Tobacco-Exposed: Results from the United States Cluster Headache Survey

OBJECTIVE

To present results from the United States Cluster Headache Survey comparing the clinical presentation of tobacco nonexposed and tobacco-exposed cluster headache patients.

BACKGROUND

Cluster headache is uniquely tied to a personal history of tobacco usage/cigarette smoking and, if the individual cluster headache sufferer did not smoke, it has been shown that their parent(s) typically did and that individual had significant secondary smoke exposure as a child. The true nontobacco exposed (no personal or secondary exposure) cluster headache sufferer has never been fully studied.

METHODS

The United States Cluster Headache Survey consisted of 187 multiple choice questions related to cluster headache including: patient demographics, clinical headache characteristics, family history, triggers, smoking history (personal and secondary), and headache-related disability. The survey was placed on a website from October through December 2008.

RESULTS

One thousand one hundred thirty-four individuals completed the survey. One hundred thirty-three subjects or 12% of the surveyed population had no personal smoking/tobacco use history and no secondary smoke exposure as an infant/child, thus a nontobacco exposed population. In the nonexposed population, there were 87 males and 46 females with a gender ratio of 1.9:1. Episodic cluster headache occurred in 80% of nonexposed subjects. One thousand and one survey responders or 88% were tobacco-exposed (729 males and 272 females) with a gender ratio of 2.7:1. Eighty-three percent had a personal smoking history, while only 17% just had parents who smoked with secondary smoke exposure. Eighty-five percent of smokers had double exposure with a personal smoking history and secondary exposure as a child.

SIGNIFICANT HIGHLIGHTS FROM THE SURVEY

Nonexposed cluster headache subjects are significantly more likely to develop cluster headache at ages 40 years and younger, while the exposed sufferers are significantly more likely to develop cluster headache at 40 years of age and older. Nonexposed patients have a statistically significant higher frequency of a migraine family history. The exposed population is statistically significantly more likely to have a history of head trauma 19% vs the nonexposed population 10% (P = .02). Tobacco exposed are significantly more likely to transition from episodic to chronic cluster headache (23% vs 14%, P = .02). Cranial autonomic symptoms as well as agitation are more common in tobacco exposed. Nonexposed are less likely to have specific cluster headache triggers. Exposed are significantly more likely to be triggered by alcohol. Tobacco exposed are significantly heavier caffeine users than nonexposed. Nonexposed are significantly more likely to have cluster headache cycles that vary throughout the year than exposed (52% vs 40%, P = .02). Exposed are much more likely to develop cluster headache from 12 am to 6 am than non exposed. Exposed experience significantly more frequent attacks per day and longer duration cycles than nonexposed. A significantly larger percent of the exposed population (57%) has suicidal ideations with their syndrome than nonexposed (43%) (P = .003). In regard to disability, both subtypes are disabled by their headaches, but exposed have more work related disability and lost home-days from headache. Both subgroups have a poor overall response to preventive and abortive medication outside of inhaled oxygen and injectable sumatriptan.

CONCLUSION

Cluster headache sufferers who were never exposed to tobacco (personal or secondary as a child) appear to present uniquely compared to the tobacco exposed subgroup. The tobacco exposed clinical phenotype appears to have a more severe syndrome based on attack frequency, cycle duration, and headache related disability. Tobacco exposure is associated with cluster headache chronification. The nonexposed subtype appears to have an earlier age of onset, higher rate of familial migraine, and less circadian periodicity and daytime entrainment, suggesting a possible different underlying pathology than in the tobacco exposed sub-form.

Biology of Neuropeptides: Orexinergic Involvement in Primary Headache Disorders

Migraine is a very common, severe disabling condition that can last for days and strike multiple times per month. Attacks, often characterized by severe unilateral throbbing pain that is exacerbated by activity, are commonly preceded by several diverse symptoms including fatigue, irritability, and yawning. This premonitory (prodromal) phase represents the earliest identifiable feature of an attack that is a reliable predictor of ensuing headache. The diversity of these symptoms underlines the complex nature of migraine and focuses considerable attention on the hypothalamus due to its prominent role in homeostatic regulation allowing state dependent behavioral modifications. While multiple neurotransmitter and neuropeptide systems have been proposed to play a role in migraine, the current review will focus on the emerging role of the hypothalamic orexinergic system in primary headache disorders. Specifically the potential role of altered orexinergic signalling in premonitory symptomatology and the future potential of targeted orexinergic therapies that could with other approaches act during the premonitory phase to prevent the occurrence of the headache or reduce an individual's susceptibility to attacks by altering the brain's response to external and internal triggers.

Cluster headache

Cluster headache is an excruciating, strictly one-sided pain syndrome with attacks that last between 15 minutes and 180 minutes and that are accompanied by marked ipsilateral cranial autonomic symptoms, such as lacrimation and conjunctival injection. The pain is so severe that female patients describe each attack as worse than childbirth. The past decade has seen remarkable progress in the understanding of the pathophysiological background of cluster headache and has implicated the brain, particularly the hypothalamus, as the generator of both the pain and the autonomic symptoms. Anatomical connections between the hypothalamus and the trigeminovascular system, as well as the parasympathetic nervous system, have also been implicated in cluster headache pathophysiology. The diagnosis of cluster headache involves excluding other primary headaches and secondary headaches and is based primarily on the patient's symptoms. Remarkable progress has been achieved in developing effective treatment options for single cluster attacks and in developing preventive measures, which include pharmacological therapies and neuromodulation.

Genetic association of HCRTR2, ADH4 and CLOCK genes with cluster headache: a Chinese population-based case-control study

Background

Cluster headache (CH), a rare primary headache disorder, is currently thought to be a genetic susceptibility which play a role in CH susceptibility. A large numbers of genetic association studies have confirmed that the HCRTR2 (Hypocretin Receptor 2) SNP rs2653349, and the ADH4 (Alcohol Dehydrogenase 4) SNP rs1126671 and rs1800759 polymorphisms are linked to CH. In addition, the CLOCK (Circadian Locomotor Output Cycles Kaput) gene is becoming a research hotspot for CH due to encoding a transcription factor that serves as a basic driving force for circadian rhythm in humans. The purpose of this study was to evaluate the association between CH and the HCRTR2, ADH4 and CLOCK genes in a Chinese CH case–control sample.

Methods

We genotyped polymorphisms of nine single nucleotide polymorphisms (SNPs) in the HCRTR2, ADH4 and CLOCK genes to perform an association study on a Chinese Han CH case-control sample (112 patients and 192 controls),using Sequenom MALDI-TOF mass spectrometry iPLEX platform. The frequencies and distributions of genotypes and haplotypes were statistically compared between the case and control groups to identify associations with CH. The effects of SNPs on CH were further investigated by multiple logistic regression.

Results

The frequency of the HCRTR2 SNP rs3800539 GA genotype was significantly higher in cases than in controls (48.2% vs.37.0%). The GA genotypes was associated with a higher CH risk (OR = 1.483, 95% CI: 0.564-3.387, p = 0.038), however, after Bonferroni correction, the association lost statistical significance. Haplotype analysis of the HCRTR2 SNPs showed that among eight haplotypes, only H1-GTGGGG was linked to a reduced CH risk (44.7% vs. 53.1%, OR = 0.689, 95% CI =0.491~0.966, p = 0.030). No significant association of ADH4, CLOCK SNPs with CH was statistically detected in the present study.

Conclusions

Association between HCRTR2, ADH4,CLOCK gene polymorphisms and CH was not significant in the present study, however, haplotype analysis indicated H1-GTGGGG was linked to a reduced CH risk.

Electronic supplementary material

The online version of this article (10.1186/s10194-017-0831-1) contains supplementary material, which is available to authorized users.

Diagnosis, pathophysiology, and management of cluster headache

Cluster headache is a trigeminal autonomic cephalalgia characterised by extremely painful, strictly unilateral, short-lasting headache attacks accompanied by ipsilateral autonomic symptoms or the sense of restlessness and agitation, or both. The severity of the disorder has major effects on the patient's quality of life and, in some cases, might lead to suicidal ideation. Cluster headache is now thought to involve a synchronised abnormal activity in the hypothalamus, the trigeminovascular system, and the autonomic nervous system. The hypothalamus appears to play a fundamental role in the generation of a permissive state that allows the initiation of an episode, whereas the attacks are likely to require the involvement of the peripheral nervous system. Triptans are the most effective drugs to treat an acute cluster headache attack. Monoclonal antibodies against calcitonin gene-related peptide, a crucial neurotransmitter of the trigeminal system, are under investigation for the preventive treatment of cluster headache. These studies will increase our understanding of the disorder and perhaps reveal other therapeutic targets.

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.

Identifying a gene expression signature of cluster headache in blood

Cluster headache is a relatively rare headache disorder, typically characterized by multiple daily, short-lasting attacks of excruciating, unilateral (peri-)orbital or temporal pain associated with autonomic symptoms and restlessness. To better understand the pathophysiology of cluster headache, we used RNA sequencing to identify differentially expressed genes and pathways in whole blood of patients with episodic (n = 19) or chronic (n = 20) cluster headache in comparison with headache-free controls (n = 20). Gene expression data were analysed by gene and by module of co-expressed genes with particular attention to previously implicated disease pathways including hypocretin dysregulation. Only moderate gene expression differences were identified and no associations were found with previously reported pathogenic mechanisms. At the level of functional gene sets, associations were observed for genes involved in several brain-related mechanisms such as GABA receptor function and voltage-gated channels. In addition, genes and modules of co-expressed genes showed a role for intracellular signalling cascades, mitochondria and inflammation. Although larger study samples may be required to identify the full range of involved pathways, these results indicate a role for mitochondria, intracellular signalling and inflammation in cluster headache.

A genome-wide analysis in cluster headache points to neprilysin and PACAP receptor gene variants

Background

Cluster Headache (CH) is a severe primary headache, with a poorly understood pathophysiology. Complex genetic factors are likely to play a role in CH etiology; however, no confirmed gene associations have been identified. The aim of this study is to identify genetic variants influencing risk to CH and to explore the potential pathogenic mechanisms.

Methods

We have performed a genome-wide association study (GWAS) in a clinically well-defined cohort of 99 Italian patients with CH and in a control sample of 360 age-matched sigarette smoking healthy individuals, using the Infinium PsychArray (Illumina), which combines common highly-informative genome-wide tag SNPs and exonic SNPs. Genotype data were used to carry out a genome-wide single marker case-control association analysis using common SNPs, and a gene-based association analysis focussing on rare protein altering variants in 745 candidate genes with a putative role in CH.

Results

Although no single variant showed statistically significant association at the genome-wide threshold, we identified an interesting suggestive association (P = 9.1 × 10⁻⁶) with a common variant of the PACAP receptor gene (ADCYAP1R1). Furthermore, gene-based analysis provided significant evidence of association (P = 2.5 × 10⁻⁵) for a rare potentially damaging missense variant in the MME gene, encoding for the membrane metallo-endopeptidase neprilysin.

Conclusions

Our study represents the first genome-wide association study of common SNPs and rare exonic variants influencing risk for CH. The most interesting results implicate ADCYAP1R1 and MME gene variants in CH susceptibility and point to a role for genes involved in pain processing. These findings provide new insights into the pathogenesis of CH that need further investigation and replication in larger CH samples.

Electronic supplementary material

The online version of this article (doi:10.1186/s10194-016-0705-y) contains supplementary material, which is available to authorized users.

Lack of association between cluster headache and PER3 clock gene polymorphism

Background

Cluster headache (CH) is regarded as a chronobiological disorder. The hypothalamic biological clock may thus be involved in the pathophysiology, but few studies have actually investigated this in CH patients. A variable number tandem repeat (VNTR) polymorphism of the PER3 clock gene has been associated to preferred daily rhythm (chronotype) in several studies. We aimed to study the distribution of PER3 VNTR polymorphisms and chronotypes in a CH population.

Methods

We used blood samples from a biobank of CH patients for genetic tests, and invited all tested patients to complete the Horne-Ostberg Morningness-eveningness Questionnaire (MEQ), the Pittsburgh sleep quality Index (PSQI) and the Shift Work Index. Genotypes were compared to a previously tested population of 432 healthy students.

Results

One hundred forty nine patients were genotyped, and we found no difference in PER3 VNTR polymorphisms between patients and controls. Seventy-four patients completed the MEQ (54 men, 20 women, mean age 52.3 years ± 13.4), and chronotypes were as follows: 12 % morning-, 37 % intermediate-, and 51 % evening types. Compared with a previous Danish study of CH patients and controls, there were no difference in chronotype distribution. Sixty percent of patients were defined as bad sleepers (PSQI >5), and 51 % of patients currently employed were shift workers.

Conclusions

No association between CH, PER3 VNTR polymorphism and chronotype was found in this study.

Neurobiology and sleep disorders in cluster headache

Cluster headache is characterized by unilateral attacks of severe pain accompanied by cranial autonomic features. Apart from these there are also sleep-related complaints and strong chronobiological features. The interaction between sleep and headache is complex at any level and evidence suggests that it may be of critical importance in our understanding of primary headache disorders. In cluster headache several interactions between sleep and the severe pain attacks have already been proposed. Supported by endocrinological and radiological findings as well as the chronobiological features, predominant theories revolve around central pathology of the hypothalamus. We aimed to investigate the clinical presentation of chronobiological features, the presence of concurrent sleep disorders and the relationship with particular sleep phases or phenomena, the possible role of hypocretin as well as the possible involvement of cardiac autonomic control. We conducted a questionnaire survey on 275 cluster headache patients and 145 controls as well an in-patient sleep study including 40 CH-patients and 25 healthy controls. The findings include: A distinct circannual connection between cluster occurrence and the amount of daylight, substantially poorer sleep quality in patients compared to controls which was present not only inside the clusters but also outside, affected REM-sleep in patients without a particular temporal connection to nocturnal attacks, equal prevalence of sleep apnea in both patient and control groups, reduced levels of hypocretin-1 in the cerebrospinal fluid of patients and finally a blunted response to the change from supine to tilted position in the head-up tilt table test indicating a weakened sympathoexcitatory or stronger parasympathetic drive. Overall, these findings support a theory of involvement of dysregulation in hypothalamic and brainstem nuclei in cluster headache pathology. Further, it is made plausible that the headache attacks are but one aspect of a more complex syndrome of central dysregulation manifesting as sleep-related complaints, sub-clinical autonomic dysregulation and of course the severe attacks of unilateral headache. Future endeavors should focus on pathological changes which persist in the attack-free periods but also heed the possibility of long-lived, cluster-induced pathology.