5-HTTLPR polymorphism in the serotonin transporter gene and migraine: a systematic review and meta-analysis

Serotonin Transporter (5-Hydroxytryptamine Transporter, SERT, SLC6A4) and Sodium-dependent Reuptake Inhibitors as Modulators of Pain Behaviors and Analgesic Responses

The serotonin transporter (5-hydroxytryptamine transporter [5-HTT], Serotonin Transporter (SERT), SLC6A4) modulates the activity of serotonin via sodium-dependent reuptake. Given the established importance of serotonin in the control of pain, 5-HTT has received much interest in studies of pain states and as a pharmacological target for serotonin reuptake inhibitors (SRIs). Animal models expressing varying levels of 5-HTT activity show marked differences in pain behaviors and analgesic responses, as well as many serotonin-related physiological effects. In humans, functional nucleotide variations in the SLC6A4 gene, which encodes the serotonin transporter 5-HTT, are associated with certain pathologic pain conditions and differences in responses to pharmacological therapy. These findings collectively reflect the importance of 5-HTT in the intricate physiology and management of pain, as well as the scientific and clinical challenges that need to be considered for the optimization of 5-HTT-related analgesic therapies. PERSPECTIVE: The serotonin transporter 5-HTT/SCL6A4 is sensitive to pharmacological SRIs. Experimental studies on the physiological functions of serotonin, as well as genetic mouse models and clinical phenotype/genotype correlations of nucleotide variation in the human 5-HTT/SCL6A4 gene, provide new insights for the use of SRIs in chronic pain management.

Understanding the Biological Relationship between Migraine and Depression

Migraine is a highly prevalent neurological disorder. Among the risk factors identified, psychiatric comorbidities, such as depression, seem to play an important role in its onset and clinical course. Patients with migraine are 2.5 times more likely to develop a depressive disorder; this risk becomes even higher in patients suffering from chronic migraine or migraine with aura. This relationship is bidirectional, since depression also predicts an earlier/worse onset of migraine, increasing the risk of migraine chronicity and, consequently, requiring a higher healthcare expenditure compared to migraine alone. All these data suggest that migraine and depression may share overlapping biological mechanisms. Herein, this review explores this topic in further detail: firstly, by introducing the common epidemiological and risk factors for this comorbidity; secondly, by focusing on providing the cumulative evidence of common biological aspects, with a particular emphasis on the serotoninergic system, neuropeptides such as calcitonin-gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), substance P, neuropeptide Y and orexins, sexual hormones, and the immune system; lastly, by remarking on the future challenges required to elucidate the etiopathological mechanisms of migraine and depression and providing updated information regarding new key targets for the pharmacological treatment of these clinical entities.

Association analysis of serotonin transporter gene polymorphism among the South-Indian migraineurs

Background: Migraine is a multifactorial neurological disorder characterized by frequent moderate to severe intensity headaches. The genetic variations in synaptic and post-receptor signalling proteins have direct effect on the process of serotonergic neurotransmission. Methods: We aimed to investigate the genetic association of serotonin transporter (SERT) 5-hydroxytryptamine transporter-linked promoter region (5-HTTLPR) polymorphism and migraine risk in South-Indian population. A total of 304 subjects with migraine including with aura (MA) and without aura (MO) and 308 controls were included in the present study. The single nucleotide polymorphism (SNP) was detected using polymerase chain reaction (PCR) and confirmed by deoxyribonucleic acid (DNA) sequencing. Results: The genotyping analysis revealed insignificant relationship with migraine subjects when compared with controls (P > 0.05). The minor 'S' allele showed no association with odds ratio (OR) = 1.23 [95% confidence interval (CI): 0.90-1.66], heterozygote with OR = 1.18 (95% CI: 0.82-1.69), and homozygote with OR = 1.51 (95% CI: 0.52-4.35). Conclusion: Further clinical studies are required to validate the results of SERT 5-HTTLPR promoter polymorphism in diverse ethnic descents especially in Asian populations.

Correlation between 5-HTTLPR gene polymorphism and cognitive function of traumatic stress in Chinese Han children

BACKGROUND

Post-traumatic stress disorder (PTSD) is a trauma-related psychological disorder with serious social and familial impacts. The involvement of 5-hydroxytryptamine transporter gene-linked polymorphic region (5-HTTLPR) in numerous mental disorders has been documented. This study explored the correlation between 5-HTTLPR gene polymorphism and cognitive function in Chinese Han children with PTSD.

METHODS

A total of 60 PTSD children treated from December 2019 to December 2021 were selected as study participants, with another 60 healthy children selected as controls. We assessed the cognitive function of participants using the Mini-Mental State Examination (MMSE). Additionally, the PTSD level was estimated by the Children's Revised Impact of Event Scale (CRIES). The 5-HTTLPR gene polymorphism was detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR). The genotype and allele frequency were evaluated via case-control association analysis.

RESULTS

Children in the PTSD group showed low MMSE scores and high CRIES scores. In terms of genotype, cases of LL, LS, and SS in PTSD children were 4 (6.67%), 20 (33.3%), and 36 (60.00%), and 18 (30.00%), 28 (46.67%), and 14 (23.33%) cases in healthy controls. In terms of allele gene frequency, incidences of L and S were 23.33% and 76.67% in PTSD children, respectively, and were 53.33% and 46.67% in healthy controls, respectively. Moreover, the CRIES and MMSE scores of LS and SS genotypes were evidently different from those of LL genotype in PTSD children.

CONCLUSIONS

Polymorphism of the 5-HTTLPR gene is correlated with cognitive dysfunction in Chinese Han children with PTSD.

Sex and the serotonergic underpinnings of depression and migraine

Most psychiatric disorders demonstrate sex differences in their prevalence and symptomatology, and in their response to treatment. These differences are particularly pronounced in mood disorders. Differences in sex hormone levels are among the most overt distinctions between males and females and are thus an intuitive underpinning for these clinical observations. In fact, treatment with estrogen and testosterone was shown to exert antidepressant effects, which underscores this link. Changes to monoaminergic signaling in general, and serotonergic transmission in particular, are understood as central components of depressive pathophysiology. Thus, modulation of the serotonin system may serve as a mechanism via which sex hormones exert their clinical effects in mental health disorders. Over the past 20 years, various experimental approaches have been applied to identify modes of influence of sex and sex hormones on the serotonin system. This chapter provides an overview of different molecular components of the serotonin system, followed by a review of studies performed in animals and in humans with the purpose of elucidating sex hormone effects. Particular emphasis will be placed on studies performed with positron emission tomography, a method that allows for human in vivo molecular imaging and, therefore, assessment of effects in a clinically representative context. The studies addressed in this chapter provide a wealth of information on the interaction between sex, sex hormones, and serotonin in the brain. In general, they offer evidence for the concept that the influence of sex hormones on various components of the serotonin system may serve as an underpinning for the clinical effects these hormones demonstrate.

Genetic variants in migraine: a field synopsis and systematic re-analysis of meta-analyses

OBJECTIVE

Numerous genetic variants from meta-analyses of observational studies and GWAS were reported to be associated with migraine susceptibility. However, due to the random errors in meta-analyses, the noteworthiness of the results showing statistically significant remains doubtful. Thus, we performed this field synopsis and re-analysis study to evaluate the noteworthiness using a Bayesian approach in hope of finding true associations.

METHODS

Relevant meta-analyses from observational studies and GWAS examining correlation between all genetic variants and migraine risk were included in our study by a PubMed search. Identification of noteworthy associations were analyzed by false-positive rate probability (FPRP) and Bayesian false discovery probability (BFDP). Using noteworthy variants, GO enrichment analysis were conducted through DAVID online tool. Then, the PPI network and hub genes were performed using STRING database and CytoHubba software.

RESULTS

As for 8 significant genetic variants from observational studies, none of which showed noteworthy at prior probability of 0.001. Out of 47 significant genetic variants in GWAS, 36 were noteworthy at prior probability of 0.000001 via FPRP or BFDP. We further found the pathways "positive regulation of cytosolic calcium ion concentration" and "inositol phosphate-mediated signaling" and hub genes including MEF2D, TSPAN2, PHACTR1, TRPM8 and PRDM16 related to migraine susceptibility.

CONCLUSION

Herein, we have identified several noteworthy variants for migraine susceptibility in this field synopsis. We hope these data would help identify novel genetic biomarkers and potential therapeutic target for migraine.

Correlation Between Salivary, Platelet and Central Serotonin Levels in Children

Background:

Serotonin (5-HT) is a neurotransmitter synthesized in both the central nervous system (CNS) and in enterochromaffin cells of the gut. 5-HT biosynthesis is separate between the periphery and the CNS. Any observed correlations between centrally and peripherally measured 5-HT remain to be elucidated. Previous efforts have looked for a noninvasive marker of central serotonin, including serotonin in whole blood, plasma, platelets, saliva, and urine; however, results are conflicting.

Aim:

Finding a noninvasive marker for central serotonin turnover that can be used for diagnosis and therapeutic monitoring in patients with primary neurotransmitter deficiencies.

Methods:

Inclusion criterion was all children presenting with neurological symptoms whose clinical investigations included lumbar puncture (LP) for cerebrospinal fluid (CSF) collection and neurotransmitter metabolite analysis, were recruited. For central serotonin turnover, the serotonin metabolite 5-hydroxyindoleacetic acid (5HIAA) was used. Bivariate correlation between the serotonin levels in CSF (5HIAA), platelets, and saliva was calculated.

Results:

Twenty-six patients (aged 6 months to 15 years) with various neurologic presentations had LP for CSF collection and neurotransmitter metabolite analysis as part of their clinical care. An additional salivary and blood sample was obtained at the same time. Eighteen patients had suitable samples for quantitative measure of serotonin. There was no correlation between platelet serotonin and CSF 5HIAA levels (Pearson’s coefficient of correlation – PCC: 0.010) or between salivary serotonin and CSF 5HIAA (PCC: 0.258). There was a strong negative correlation between salivary and platelet serotonin (PCC: −0.679).

Conclusion:

Our findings suggest that salivary serotonin measurement is not a suitable noninvasive marker for measuring central serotonin turnover.

The exploration of mechanisms of comorbidity between migraine and depression

Migraine comorbid with depression is common and is often encountered in clinical practice. The comorbidity may lead to more serious conditions with other symptoms and a longer duration of treatment and it may impose heavy economic and social burdens, directly or indirectly, on patients and their families. Numerous studies have been published on the association of migraine with depression. Numerous literature have showed that the comorbidity may have a common complicated pathogenic mechanism involving biopsychosocial characteristics, including abnormal brain development and shared genetic basis, as well as neurotransmitters, sex hormones and stress. In addition, some studies have identified the multiple, bidirectional relationship between migraine and depressive disorder. We searched the literature for the possible common mechanisms between migraine and depression and classified the research results.

Impact of serotonin transporter gene on rTMS augmentation of SSRIs for obsessive compulsive disorder

OBJECTIVE

Repetitive transcranial magnetic stimulation (rTMS) is beneficial for treatment-resistant patients with obsessive-compulsive disorder (OCD). The serotonin transporter gene (SLC6A4) may be associated with OCD. We aimed to determine whether SLC6A4 impacts the beneficial effects of rTMS in patients with OCD treated with selective serotonin reuptake inhibitors (SSRIs).

METHODS

Fifty-seven untreated patients with OCD were randomly assigned to receive active or sham rTMS in a 4-week double-blind study. The participants received 1-Hz rTMS over the supplementary motor area once per day, for 5 days a week, for 4 weeks. One of the widely employed SSRIs was utilized at the initiation of active or sham rTMS. Yale-Brown obsessive-compulsive scale (Y-BOCS) scores were used for assessing the symptoms. The most-researched polymorphism of SLC6A4, 5-HTTLPR (L/S), was also examined.

RESULTS

Y-BOCS scores in the active group at the completion of the treatment were significantly lower than those in the sham group. Interestingly, the improvement in Y-BOCS scores in patients with the LL genotype treated with active rTMS was significantly (p<0.05) greater than in those treated with sham rTMS. Conversely, rTMS did not produce significant improvements in S allele carriers.

CONCLUSIONS

The findings of this study suggest that rTMS can augment the beneficial effects of SSRIs in OCD patients with the LL genotype of 5-HTTLPR. Therefore, the presence of 5-HTTLPR (L/S) in SLC6A4 may be a predictable biomarker for the beneficial effects of rTMS, although more studies using larger sample sizes are warranted for confirming the results.

The New *G29A and G1222A of HCRTR1, 5-HTTLPR of SLC6A4 Polymorphisms and Hypocretin-1, Serotonin Concentrations in Migraine Patients

Migraine is one of the most common primary headache disorders that affects 11% of the adult population. The disease is divided into two main clinical subtypes: migraine with aura (MA) and migraine without aura (MO). Both serotonergic and hypocretinergic systems are involved in the migraine pathomechanism. Polymorphisms in the serotonin transporter gene (SLC6A4) and the hypocretin receptor 1 gene (HCRTR1) may be risk factors for migraine development due to their ability to affect serotonin and hypocretin-1 (HCRT-1) concentrations. The aim of the study was to analyze, for the first time in the Polish population, the 5-HT transporter linked polymorphic region (5-HTTLPR) in SLC6A4, G1222A (rs2271933) and the never before studied *G29A (rs41263963) polymorphisms in the HCRTR1 gene, as well as the 5-HT and hypocretin-1 plasma concentrations in migraine patients (MA, MO) and control subjects. The study included 123 patients that were diagnosed with migraine and 123 control subjects. Methods such as PCR, HRMA and sequencing were used for genotyping, while 5-HT was determined by HPLC/EC and hypocretin-1 by ELISA. No significant differences were observed in 5-HTTLPR frequencies. The A allele of HCRTR1 G1222A occurred more often in MO, while the GA genotype of HCRTR1 *G29A was more frequent among MA when compared to control group (p < 0.05). The mean age of migraine onset in individuals with HCRTR1 *G29A was 18 years old for patients with MA and 26 years old for MO patients. The localization and type of HCRTR1 polymorphisms (G1222A-missense variant in exon 7, *G29A-3'UTR variant) may predispose patients to the clinical subtype of migraine: MO or MA, respectively. In control subjects, the short allele of 5-HTTLPR tended to decrease the 5-HT concentration, while the A allele of HCRTR1 G1222A decreased both 5-HT and hypocretin-1 levels. Serotonin concentrations differed in terms of clinical features of migraine. The relation between genotypes of 5-HTTLPR, HCRTR1 G1222A, and 5-HT concentrations may bedisturbed in migraine. It seems that HCRTR1 *G29A is more strongly associated with regulating the 5-HT in patients with MA than MO, and therefore may contribute to the early age of onset for migraine.

Genetic and biochemical changes of the serotonergic system in migraine pathobiology

Migraine is a brain disorder characterized by a piercing headache which affects one side of the head, located mainly at the temples and in the area around the eye. Migraine imparts substantial suffering to the family in addition to the sufferer, particularly as it affects three times more women than men and is most prevalent between the ages of 25 and 45, the years of child rearing. Migraine typically occurs in individuals with a genetic predisposition and is aggravated by specific environmental triggers. Attempts to study the biochemistry of migraine began as early as the 1960s and were primarily directed at serotonin metabolism after an increase of 5-hydroxyindoleacetic acid (5-HIAA), the main metabolite of serotonin was observed in urine of migraineurs. Genetic and biochemical studies have primarily focused on the neurotransmitter serotonin, considering receptor binding, transport and synthesis of serotonin and have investigated serotonergic mediators including enzymes, receptors as well as intermediary metabolites. These studies have been mainly assayed in blood, CSF and urine as the most accessible fluids. More recently PET imaging technology integrated with a metabolomics and a systems biology platform are being applied to study serotonergic biology. The general trend observed is that migraine patients have alterations of neurotransmitter metabolism detected in biological fluids with different biochemistry from controls, however the interpretation of the biological significance of these peripheral changes is unresolved. In this review we present the biology of the serotonergic system and metabolic routes for serotonin and discuss results of biochemical studies with regard to alterations in serotonin in brain, cerebrospinal fluid, saliva, platelets, plasma and urine of migraine patients.

Physiologic and Psychologic Risk Factors in Central Serous Chorioretinopathy

PURPOSE

Central serous chorioretinopathy (CSCR) is characterized by macular detachment due to thickened choroid, mostly affecting young men under perceived stress. Although most previous studies on CSCR have been retrospective and have focused on a single facet of the patient's personality, we conducted a prospective, intercontinental, controlled study to analyze the multifaceted personality profile in CSCR.

DESIGN

Prospective, cross-sectional, case-control study.

PARTICIPANTS

Subjects with CSCR from 6 university-based eye clinics consented to participate in a questionnaire. Controls without retinal disease were recruited from the same clinics.

METHODS

The interview consisted of a 60-item questionnaire. Recruitment of participants was from January 2015 to February 2016. Controls were matched for age, gender, and race. Statistical analyses were performed using univariate and multivariate analyses.

MAIN OUTCOME MEASURES

The main parameters registered were presence of stress, daily number of cups caffeine intake, and personality traits (Type A; obsessive-compulsive; aggressive).

RESULTS

A total of 83 consecutive patients with CSCR (mean age, 45.9 years; male, 80.7%) and 83 controls (mean age, 46.0 years; male, 80.7%) were analyzed for 60 variables. Multivariate analysis revealed a strong association with obsessive-compulsive behavior (P = 0.001), caffeine intake (P = 0.002), Type A personality (P = 0.002), continuous stress (P = 0.001), and premature ejaculation (P = 0.001).

CONCLUSIONS

This study sheds light on the unique psychologic functioning of patients with CSCR: preoccupied, inflexible, perfectionist (obsessive-compulsive tendency), competitive, ambitious, impatient, high achiever (Type A personality), and under continuous stress. In addition, caffeine abuse and premature ejaculation were linked to CSCR.

Molecular factors in migraine

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

Childhood Maltreatment in the Migraine Patient

OPINION STATEMENT

Maltreatment during childhood increases vulnerability to a host of health disorders, including migraine. Putative mechanisms linking maltreatment and migraine include stress-induced dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, as well as disruption of other stress-mediating homeostatic systems, including those involving endocannabinoids, monoamine neurotransmitters, oxytocin, and inflammation. Prolonged elevation of glucocorticoids alters the neural architecture of the limbic system, resulting in the structural as well as functional changes described in both maltreatment and in migraine. Although treatment trials for migraine have not stratified participants by abuse history, strategies, such as cognitive behavioral therapy, which alter stress responsivity, may be particularly effective in this subgroup. Some therapies involving the endocannabinoid, serotonergic, oxytonergic, and inflammatory systems are under investigation for migraine. Anti-epileptic drugs such as valproate and topiramate, which are FDA approved for migraine treatment, are also known to interfere with epigenetic changes induced by stress. Discerning the role for this mechanism in treatment of maltreated migraineurs may introduce another therapeutic avenue.

Genetic epidemiology of migraine and depression

Background

Migraine and major depressive disorder (commonly referred to as depression) are both common disorders with a significant impact on society. Studies in both clinical and community-based settings have demonstrated a strong relationship between migraine and depression. In addition to complicating the diagnosis, depression that is comorbid with migraine may lower treatment adherence, increase risk of medication overuse and is associated with migraine chronification, thus leading to higher direct and indirect costs and poorer health-related outcomes with increased disability.

Aim

The aim of this review is to summarise the current knowledge on the genetic epidemiology of migraine and depression and the possible biological mechanisms underlying their comorbidity.

Methods

We present a narrative review reporting on the current literature.

Results and conclusions

Epidemiological findings indicate that there is a bidirectional relationship between migraine and depression, with one disorder increasing the risk for the other and vice versa, suggesting shared biological mechanisms. Twin and family studies indicate that this bidirectional relationship can be explained, at least partly, by shared underlying genetically determined disease mechanisms. Although no genes have been robustly associated with the aetiology of both migraine and depression, genes from serotonergic, dopaminergic and GABAergic systems together with variants in the MTHFR and BDNF genes remain strong candidates.

Folate Pathway Gene Methylenetetrahydrofolate Reductase C677T Polymorphism and Alzheimer Disease Risk in Asian Population

The association between methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and susceptibility to Alzheimers disease (AD) was controversial in previous studies. The present meta-analysis was designed to investigate the association of MTHFR C677T polymorphism with AD. Nine studies were identified by search of PubMed, Google Scholar, Elsevier, Springer Link databases, up to January 2013. Odds ratios (ORs) with corresponding 95 % confidence interval (CI) were calculated using fixed effects model or random effects model. All statistical analysis was done by Mix version 1.7. MTHFR C677T polymorphism had a significant association with susceptibility to AD in all genetic models (for T vs C: OR 1.29, 95 % CI 1.15-1.44, p < 0.0001; for TT + CT vs CC: OR 1.38, 95 % CI 1.16-1.364, p = 0.0002; for TT vs CC: OR 1.60, 95 % CI 1.25-2.04, p = 0.0001; for CT vs CC: OR 1.28, 95 % CI 1.1-1.53, p < 0.008; for TT vs CT + CC: OR 1.37, 95 % CI 1.12-1.67, p = 0.002). Results from present meta-analysis supported that the MTHFR C677T polymorphism was associated with an increased risk of AD in Asian population.

Genome wide association study identifies variants in NBEA associated with migraine in bipolar disorder

BACKGROUND

Migraine is a common comorbidity among individuals with bipolar disorder, but the underlying mechanisms for this co-occurrence are poorly understood. The aim of this study was to investigate the genetic background of bipolar patients with and without migraine.

METHODS

We performed a genome-wide association analysis contrasting 460 bipolar migraneurs with 914 bipolar patients without migraine from the Bipolar Genome Study (BiGS).

RESULTS

We identified one genome-wide significant association between migraine in bipolar disorder patients and rs1160720, an intronic single nucleotide polymorphism (SNP) in the NBEA gene (P=2.97 × 10(-8), OR: 1.82, 95% CI: 1.47-2.25), although this was not replicated in a smaller sample of 289 migraine cases.

LIMITATIONS

Our study is based on self-reported migraine.

CONCLUSIONS

NBEA encodes neurobeachin, a scaffolding protein primarily expressed in the brain and involved in trafficking of vesicles containing neurotransmitter receptors. This locus has not previously been implicated in migraine per se. We found no evidence of association in data from the GWAS migraine meta-analysis consortium (n=118,710 participants) suggesting that the association might be specific to migraine co-morbid with bipolar disorder.

Serotonin, 5HT1 agonists, and migraine: new data, but old questions still not answered

PURPOSE OF REVIEW

The serotonergic system has long been linked to migraine but recent studies highlight how much is still unclear about this link. And recent data add to the uncertainty of where/how triptans act and why they are headache specific.

RECENT FINDINGS

Markers of 5HT levels in the brains of migraine patients show no changes between attacks. Several recent meta-analyses show the most convincing data on genetic differences in the serotonergic system for 5HT transporters. Findings of additional triptan actions on peripheral trigeminovascular neurons and in the hypothalamus add more fuel to the debate on where these drugs act. A growing list of studies show efficacy of multiple triptans and other 5HT1b/1d agonists in preclinical models of nonheadache pain arguing for reevaluation of whether these drugs have efficacy in other pain states. Despite these issues, serotonergic drugs continue to be the gold standard for abortive agents with new members on the horizon (5HT1f agonists).

SUMMARY

Given the clear efficacy of serotonergic drugs for migraine, continued study on the role of the endogenous 5HT system may lead to more novel therapies. And with the list of studies demonstrating efficacy triptans in models of nonheadache, clinical studies should address whether these drugs work for other types of pain.

Bi-allelic and tri-allelic 5-HTTLPR polymorphisms and triptan non-response in cluster headache

Background

Triptans are only effective in terminating cluster headache (CH) attacks in 70-80% of patients. Pharmacogenetic aspects of the serotonin metabolism, specifically variation in the 5-HTTLPR may be involved.

Methods

Genetic association study in a well-defined cohort of 148 CH patients with information on drug response to triptans. CH was diagnosed according to the criteria of the International Headache Society. Genotypes of the 43-bp insdel (rs4795541) and A > G (rs25531) polymorphisms in the 5-HTTLPR promoter region were detected by restriction fragment length polymorphism analysis. We used logistic regression analysis to investigate the association between bi-allelic and tri-allelic genotypes and triptan non-response with genotype models.

Results

Mean age at study entry among patients was 44.6 ± 10.5 years, 77.7% were men. The genotype distribution both for the bi-allelic and the tri-allelic polymorphism was in Hardy-Weinberg equilibrium. We did not find an association of the bi-allelic polymorphism with triptan non-response. While the effect estimates for the S variant of the tri-allelic polymorphisms suggested increased odds of triptan non-response in CH patients (multivariable-adjusted odds ratio [95% confidence interval]: L*L* genotype—reference; L*S* genotype—1.33 [0.53-3.32]; S*S* genotype—1.46 [0.54-3.98]), the results were not statistically significant.

Conclusions

Data from our study do not indicate a role of bi-allelic and tri-allelic genotypes of the 5-HTTLPR polymorphism in triptan non-response in CH.

Endothelial Nitric Oxide Synthase and Angiotensin Converting Enzyme Gene Polymorphisms in Migraine Patients

INTRODUCTION

In this study, we investigated the association of migraine with the Variable Number of Tandem Repeats (VNTR), repeated as 27 base pair, gene polymorphism in intron 4 of the endothelial nitric oxide synthase (eNOS) and the insertion/deletion of angiotensin converting enzyme (ACE) gene polymorphisms.

METHODS

One hundred and five migraine and ninety seven healthy female control subjects were enrolled in the study. The patients were subdivided as migraine with aura and without aura, and the frequency and severity of migraine headaches were recorded. The eNOS VNTR (eNOS 4 a/b) and ACE insertion/deletion gene polymorphisms (ACE I/D) were assessed by polymerase chain reactions.

RESULT

The allele and genotype frequencies of eNOS 4 a/b gene polymorphism showed no difference between the migraine and control groups. The genotypic distribution of the ACE I/D gene polymorphism in the migraine group significantly differed from that in the control group. The DD and ID genotype increased the risk of migraine as much as 2.571 (95% CI-1.138-5.811) and 4.453 (95% CI-2.006-9.883) compared to the II genotype. The same increased risk sustained for both genotypes in the migraine with aura subgroup, but only the ID genotype remained as the risk factor in the migraine without aura subgroup (OR-3.750, 95% CI-1.493-9.420). No association of gene polymorphisms with migraine frequency and severity was observed.

CONCLUSION

Our findings support the relationship between migraine and the ACE I/D gene polymorphism. However, no association was found between migraine and the eNOS 4 a/b gene polymorphism.

Studies on the pathophysiology and genetic basis of migraine

Migraine is a neurological disorder that affects the central nervous system causing painful attacks of headache. A genetic vulnerability and exposure to environmental triggers can influence the migraine phenotype. Migraine interferes in many facets of people's daily life including employment commitments and their ability to look after their families resulting in a reduced quality of life. Identification of the biological processes that underlie this relatively common affliction has been difficult because migraine does not have any clearly identifiable pathology or structural lesion detectable by current medical technology. Theories to explain the symptoms of migraine have focused on the physiological mechanisms involved in the various phases of headache and include the vascular and neurogenic theories. In relation to migraine pathophysiology the trigeminovascular system and cortical spreading depression have also been implicated with supporting evidence from imaging studies and animal models. The objective of current research is to better understand the pathways and mechanisms involved in causing pain and headache to be able to target interventions. The genetic component of migraine has been teased apart using linkage studies and both candidate gene and genome-wide association studies, in family and case-control cohorts. Genomic regions that increase individual risk to migraine have been identified in neurological, vascular and hormonal pathways. This review discusses knowledge of the pathophysiology and genetic basis of migraine with the latest scientific evidence from genetic studies.

Pharmacogenetics of chronic pain and its treatment

This paper reviews the impact of genetic variability of drug metabolizing enzymes, transporters, receptors, and pathways involved in chronic pain perception on the efficacy and safety of analgesics and other drugs used for chronic pain treatment. Several candidate genes have been identified in the literature, while there is usually only limited clinical evidence substantiating for the penetration of the testing for these candidate biomarkers into the clinical practice. Further, the pain-perception regulation and modulation are still not fully understood, and thus more complex knowledge of genetic and epigenetic background for analgesia will be needed prior to the clinical use of the candidate genetic biomarkers.

Emerging genomic biomarkers in migraine

Migraine is a debilitating neurovascular condition classified as either migraine with aura or migraine without aura. A significant genetic basis has been implicated in migraine and has probed the role of neurotransmitters, hormones and vascular genes in this disorder. The aim of this review is to highlight the recent genetic discoveries contributing to our understanding of the complex pathogenesis of migraine. The current review will discuss the role of neurotransmitter-related genes in migraine, including the recently identified TRESK and variants of the KCNN3 gene, as well as outlining studies investigating hormone receptor genes, such as ESR1 and PGR, and vascular-related genes, including the MTHFR and NOTCH 3 genes.

Pharmacogenetics of pain and analgesia

Pain severity ratings and the analgesic dosing requirements of patients with apparently similar pain conditions may differ considerably between individuals. Contributing factors include those of genetic and environmental origin with epigenetic mechanisms that enable dynamic gene-environment interaction, more recently implicated in pain modulation. Insight into genetic factors underpinning inter-patient variability in pain sensitivity has come from rodent heritability studies as well as familial aggregation and twin studies in humans. Indeed, more than 350 candidate pain genes have been identified as potentially contributing to heritable differences in pain sensitivity. A large number of genetic association studies conducted in patients with a variety of clinical pain types or in humans exposed to experimentally induced pain stimuli in the laboratory setting, have examined the impact of single-nucleotide polymorphisms in various target genes on pain sensitivity and/or analgesic dosing requirements. However, the findings of such studies have generally failed to replicate or have been only partially replicated by independent investigators. Deficiencies in study conduct including use of small sample size, inappropriate statistical methods and inadequate attention to the possibility that between-study differences in environmental factors may alter pain phenotypes through epigenetic mechanisms, have been identified as being significant.

Behavioural genetics of the serotonin transporter

The serotonin transporter is a key regulator of the bioavailability of serotonin and therefore any modulation in the expression or action of the transporter would be expected to have consequences on behaviour. The transporter has therefore become a target for pharmaceutical intervention in behavioural and mood disorders. The search for polymorphic variants in the transporter that would associate with neurological disorders has been extensive but has become focused on two domains which are both termed variable number tandem repeat (VNTR)polymorphisms. Both of these VNTRs are in non-coding DNA and therefore proposed to be mechanistically involved in a disorder through their ability to modulate transcriptional or post-transcriptional regulation of the transporter. The most extensively studied is in the promoter and is a bi-allelic insertion/deletion found in the 50 promoter region of the gene 1.2 kb upstream of the transcriptional start site. This VNTR, termed, 5-HTTLPR was initially identified as two variants containing either, 14 (short/deletion) or 16 (long/insertion) copies of a 22 bp repeat. A second widely studied VNTR found in the non-coding region of the transporter is located within intron 2 and comprises 9, 10 or 12 copies of a16–17 bp repeat termed, STin2.9, STin2.10 and STin2.12, respectively. These VNTR polymorphisms have been associated with a range of behavioural and psychiatric disorders including depression, OCD, anxiety and schizophrenia, however often the lack of reproducibility in different cohorts has led to debate on the actual association of the polymorphisms with this extensive range of neurological conditions. Here we review these two polymorphic VNTRs in depth and relate that to pharmaceutical response, their ability to regulate differential transporter expression, their core involvement in gene-environment interaction and their genetic association with specific disorders.

Genetics of migraine in the age of genome-wide association studies

Genetic factors importantly contribute to migraine. However, unlike for rare monogenic forms of migraine, approaches to identify genes for common forms of migraine have been of limited success. Candidate gene association studies were often negative and positive results were often not replicated or replication failed. Further, the significance of positive results from linkage studies remains unclear owing to the inability to pinpoint the genes under the peaks that may be involved in migraine. Problems hampering these studies include limited sample sizes, methods of migraine ascertainment, and the heterogeneous clinical phenotype. Three genome-wide association studies are available now and have successfully identified four new genetic variants associated with migraine. One new variant (rs1835740) modulates glutamate homeostasis, thus integrates well with current concepts of neurotransmitter disturbances. This variant may be more specific for severe forms of migraine such as migraine with aura than migraine without aura. Another variant (rs11172113) implicates the lipoprotein receptor LRP1, which may interact with neuronal glutamate receptors, thus also providing a link to the glutamate pathway. In contrast, rs10166942 is in close proximity to TRPM8, which codes for a cold and pain sensor. For the first time this links a gene explicitly implicated in pain related pathways to migraine. The potential function of the fourth variant rs2651899 (PRDM16) in migraine is unclear. All these variants only confer a small to moderate change in risk for migraine, which concurs with migraine being a heterogeneous disorder. Ongoing large international collaborations will likely identify additional gene variants for migraine.

Pain, analgesia and genetics

OBJECTIVES

In the clinical setting, there is marked intersubject variability in the intensity of pain reported by patients with apparently similar pain states, as well as widely differing analgesic dosing requirements between individuals to produce satisfactory pain relief with tolerable side-effects. Genetic and environmental factors as well as their interaction are implicated, and these are discussed in this review.

KEY FINDINGS

Pioneering work undertaken in mice more than a decade ago, showed a strong genetic contribution to levels of nociception/hypersensitivity as well as levels of antinociception produced by commonly available analgesic agents. To date more than 300 candidate 'pain' genes have been identified as potentially contributing to heritable differences in pain sensitivity and analgesic responsiveness in animals and humans, with this information available in a publicly accessible database http://www.jbldesign.com/jmogil/enter.html. Since then, many genetic association studies have been conducted in humans to investigate the possibility that single nucleotide polymorphisms (SNPs) in an individual gene may explain drug inefficacy or excessive toxicity experienced by a small subset of the whole population who have the rare allele for a particular SNP.

SUMMARY

Despite the fact that SNPs in more than 20 genes that affect pain sensitivity or contribute to interindividual variability in responses to analgesic medications have been identified in the human genome, much of the data is conflicting. Apart from deficiencies in the design and conduct of human genetic association studies, recent research from other fields has implicated epigenetic mechanisms that facilitate dynamic gene-environment communication, as a possible explanation.

Association of 5-HTT gene polymorphisms with migraine: a systematic review and meta-analysis

BACKGROUND/AIMS

Serotonin is known to play an important role in the pathogenesis of migraine, but individual genetic association studies that examine the relationship between polymorphisms of serotonin transporter (5-HTT) gene and migraine have yielded inconsistent results. This study aimed to evaluate the association between 5-HTT gene variants (including 5-HTTLPR, VNTR and SNP) and migraine using systematic review with meta-analysis.

METHODS

Relevant studies were identified by searching English and Chinese databases extensively. Allele and genotype frequencies for each included study were extracted. The odds ratio (OR) was calculated using a random-effects or fixed-effects model. Q statistic was used to evaluate homogeneity, and Egger's test and Funnel plot were used to assess publication bias. For family-based association studies, a descriptive analysis was carried out.

RESULTS

A total of 15 studies were identified for meta-analysis. It was found that the 5-HTT VNTR Stin2.12 allele or 12/12 genotype had an increased risk for migraine in the general population (Stin2.12 allele: OR, 95% CI: 1.34, 1.09-1.64, p=0.006; 12/12 genotype: OR, 95% CI: 1.55, 1.17-2.05, p=0.002), but there was no significant association between migraine and 5-HTTLPR or SNP rs2020942.

CONCLUSIONS

Existing evidence indicates that the 5-HTT VNTR polymorphism (mainly the STin2.12 genotype) is associated with an increased risk of migraine in the general population. Future studies with larger sample sizes will be necessary to confirm the present results.

STin2 VNTR polymorphism in the serotonin transporter gene and migraine: pooled and meta-analyses

Data on the association between the SLC6A4 STin2 VNTR polymorphism and migraine are conflicting. To perform pooled and meta-analyses, we searched for studies published until September 2009 using electronic databases (MEDLINE, EMBASE, Science Citation Index) and reference lists of studies. Assessment for eligibility and extraction of data was performed by two independent investigators. We extracted allele and genotype frequencies for each study. We then calculated study-specific and pooled odds ratios (OR) and 95% confidence intervals (CI) assuming allele and genotype models. We also calculated pooled ORs and 95% CIs based on study-specific effect estimates for the allele model. We included five studies investigating the association between the STin2 VNTR polymorphism and migraine. Results from the allele model suggested a protective effect against migraine for the STin2.9 and STin2.10 alleles compared to the STin2.12 allele among populations of European descent, which however was not significant. Results from the genotype model indicated a significant ~25% reduced risk for migraine among carriers of the 10/12 genotype compared with carriers of the 12/12 genotype among all study populations (OR = 0.76, 95% CI 0.60–0.97) for any migraine, which was more pronounced among populations of European descent (OR = 0.68, 95% CI 0.53–0.87). Results for migraine with and without aura were of similar magnitude, but were not statistically significant. Our results suggest a protective effect of non-STin2.12 alleles compared to STin2.12 alleles, respectively, 10/12 and 10/10 genotypes compared to the 12/12 genotype against migraine among populations of European descent. Associations in non-European populations may differ.