Point mutation in platelet mitochondrial tRNA(Leu(UUR)) in patient with cluster headache

Genomics and pharmacogenomics of cluster headache: implications for personalized management? A systematic review

The role of genetic factors in cluster headache etiology, suggested by familial and twin studies, remains ill-defined, with the exact pathophysiological mechanisms still largely elusive. This systematic review aims to synthesize current knowledge on cluster headache genetics and explore its implications for personalized treatment and prediction of treatment response. Thus, we searched PubMed, Scopus, and the Cochrane Library databases and reference lists of identified research articles, meta-analyses, and reviews to identify relevant studies up to 10 July 2024. The quality of the evidence was assessed using Newcastle-Ottawa Scale for case control studies and NIH Quality Assessment tool for Observational Cohort and Cross-Sectional Studies. The protocol of this study was registered via the Open Science Framework ( https://osf.io/cd4s3 ). Fifty-one studies were selected for the qualitative synthesis: 34 candidate gene studies, 5 GWAS, 7 gene expression studies, 4 pharmacogenetic association studies, and 1 whole genome sequencing study. The bulk of genetic evidence in cluster headache underscores the involvement of genes associated with chronobiological regulation. The most studied gene in cluster headache is the HCRTR2 , which is expressed in the hypothalamus; however, findings across studies continue to be inconclusive. Recent GWAS have uncovered novel risk loci for cluster headache, marking a significant advancement for the field. Nevertheless, there remains a need to investigate various genes involved in specific mechanisms and pathways.

The genetics and chronobiology of cluster headache

BACKGROUND/HYPOTHESIS

Cluster headache displays uniquely rhythmic patterns in its attack manifestation. This strong chronobiological influence suggests that part of the pathophysiology of cluster headache is distinctly different from migraine and has prompted genetic investigations probing these systems.

METHODS

This is a narrative overview of the cluster headache chronobiological phenotype from the point of view of genetics covering existing knowledge, highlighting the specific challenges in cluster headache and suggesting novel research approaches to overcome these.

RESULTS

The chronobiological features of cluster headache are a hallmark of the disorder and while discrepancies between study results do exist, the main findings are highly reproducible across populations and time. Particular findings in subgroups indicate that the heritability of the disorder is linked to chronobiological systems. Meanwhile, genetic markers of circadian rhythm genes have been implicated in cluster headache, but with conflicting results. However, in two recently published genome wide association studies two of the identified four loci include genes with an involvement in circadian rhythm, MER proto-oncogene, tyrosine kinase and four and a half LIM domains 5. These findings strengthen the involvement of circadian rhythm in cluster headache pathophysiology.

CONCLUSION/INTERPRETATION

Studying chronobiology and genetics in cluster headache presents challenges unique to the disorder. Researchers are overcoming these challenges by pooling various data from different cohorts and performing meta-analyses providing novel insights into a classically enigmatic disorder. Further progress can likely be made by combining deep pheno- and genotyping.

No significant association between SNPs in the CLOCK and ADH4 genes and susceptibility to cluster headaches: A systematic review and meta-analysis

BACKGROUND

The circadian locomotor output cycles kaput (CLOCK) gene and the alcohol dehydrogenase 4 (ADH4) gene are promising candidates for susceptibility to cluster headaches (CH). Associations of the three single nucleotide polymorphisms (SNPs)-CLOCK SNP rs1801260 and ADH4 SNPs rs1800759, and rs1126671-with CH were studied previously, but the results were inconsistent.

METHODS

Associations between the three SNPs (rs1801260, rs1126671, and rs1800759) and CH risk were separately assessed by pooled odds ratios (ORs) along with 95% confidence intervals (95% CIs) based on five different genetic models. Methodological quality was assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS). All statistical analyses were carried out with RevMan 5.3 software.

RESULTS

Eight studies involving 1437 CH patients and 2541 healthy controls were selected for quantitative synthesis, from five studies on CLOCK rs1801260, five on ADH4 rs1800759, and three on ADH4 rs1126671. Our pooled data did not support associations between the three SNPs (rs1801260 in the CLOCK gene, rs1800759 and rs1126671 in the ADH4 gene) and susceptibility to CH (rs1801260: OR 1.10, 95% CI: 0.95-1.28; p = 0.19; rs1800759: OR 1.06, 95% CI: 0.93-1.22; p = 0.37; and rs1126671: OR 1.09, 95% CI: 0.92-1.28; p = 0.32).

CONCLUSION

We found no significant associations between the three SNPs (rs1801260 in the CLOCK gene and rs1800759 and rs1126671 in the ADH4 gene) and the susceptibility to CH across both Caucasian and Asian ethnicities in our meta-analysis.

History of cluster headache

Objective:

To summarise the history of cluster headache evolving concepts and growing insights.

Background:

Excruciating pain, activation of the parasympathetic nervous system, and circadian rhythmicity characterise cluster headache attacks.

Results:

We find the oldest descriptions of patients suffering from the disorder in case reports of the 17th and 18th centuries. Only in the 19th and early 20th centuries did physicians start hypothesizing its cause. Initially, many researchers suspected the origin of the pain in peripheral nerves or blood vessels. However, eventually, they understood that the cause of the disease lies in the brain. In 1998, Positron emission tomography studies revealed increased activity of the posterior hypothalamus, whose role remains incompletely understood. Only recently have researchers realised that being diseased implies more than dysfunction. Recent studies analysed the consequences of cluster headache for each patient. Many struggle to deal with the disorder even in the absence of pain.

Conclusion:

Physicians have been aware of this type of pain for at least 300 years. Only when researchers studied pathological anatomy and physiology did knowledge accrue. A more comprehensive picture of the disease severity emerged when they also considered its consequences.

Experimental and Clinical Evidence of the Effectiveness of Riboflavin on Migraines

Riboflavin, a water-soluble member of the B-vitamin family, plays a vital role in producing energy in mitochondria and reducing inflammation and oxidative stress. Migraine pathogenesis includes neuroinflammation, oxidative stress, and mitochondrial dysfunction. Therefore, riboflavin is increasingly being recognized for its preventive effects on migraines. However, there is no concrete evidence supporting its use because the link between riboflavin and migraines and the underlying mechanisms remains obscure. This review explored the current experimental and clinical evidence of conditions involved in migraine pathogenesis and discussed the role of riboflavin in inhibiting these conditions. Experimental research has demonstrated elevated levels of various oxidative stress markers and pro-inflammatory cytokines in migraines, and riboflavin’s role in reducing these marker levels. Furthermore, clinical research in migraineurs showed increased marker levels and observed riboflavin’s effectiveness in reducing migraines. These findings suggest that inflammation and oxidative stress are associated with migraine pathogenesis, and riboflavin may have neuroprotective effects through its clinically useful anti-inflammatory and anti-oxidative stress properties. Riboflavin’s safety and efficacy suggests its usefulness in migraine prophylaxis; however, insufficient evidence necessitates further study.

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.

Can the effects of the mitochondrial DNA mutations found in Leber’s hereditary optic neuropathy be protective against the development of cluster headache in smokers?

Is it possible that some mitochondrial DNA (mtDNA) mutations enhance the risk of developing a headache disorder while other mutations actually confer a protective effect? Mitochondrial disorders have been linked to migraine but very rarely to cluster headache (CH). The true pathogenesis of CH is unknown but a linkage to cigarette smoking is irrefutable. Leber’s hereditary optic neuropathy is a syndrome of bilateral vision loss that typically manifests in a patient’s 20s and 30s, is male predominant, and its sufferers are heavy smokers and heavy drinkers. Tobacco exposure is so linked to the condition that only smokers appear to develop vision loss while nonsmokers remain unaffected carriers of their mutations. In essence, the Leber’s hereditary optic neuropathy population is the CH population but at present there have been no reported cases of CH in this mitochondrial subgroup. Thus, could the effects of the mtDNA mutations found in Leber’s hereditary optic neuropathy, which involve complex I of the electron transport chain, actually confer a protective effect against the development of CH? This article will delve into this theory.

Headache in mitochondrial disorders

Headache is a prominent feature in mitochondrial disorders (MIDs) but no comprehensive overview is currently available. This review aims at summarising and discussing findings concerning type, frequency, pathogenesis, and treatment of headache in MIDs. The most frequent headache types in MIDs are migraine and migraine-like headache (MLH). MLH is classified as secondary headache. More rarely, tension-type headache, trigemino-autonomic headache, or different secondary headaches can be found. Migraine or MLH may manifest with or without aura. MLH is frequently associated with an ongoing or previous stroke-like episode (SLE) or a seizure but may also occur independently of other neurological features. MLH may be associated with prolonged aura or visual phenomena after headache. Except for MLH, treatment of headache in MIDs is not at variance from other causes of headache. Beyond the broadly accepted subtype-related headache treatment, diet, cofactors, vitamins, and antioxidants may provide a supplementary benefit. Midazolam, l-arginine, or l-citrulline may be beneficial for MLH. The pathogenesis of headache in MIDs largely remains unsolved. However, since migraine and MLH respond both to triptanes, a shared pathomechanism is likely. In conclusion, migraine and MLH are the prominent headache types in MIDs. MLH may or may not be associated with current or previous SLEs. MLH is pathophysiologically different from migraine and requires treatment at variance from that of migraine with aura.

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.

Mitochondrial Dysfunction and Migraine

The molecular basis of migraine is still not completely understood. An impairment of mitochondrial oxidative metabolism might play a role in the pathophysiology of this disease, by influencing neuronal information processing. Biochemical assays of platelets and muscle biopsies performed in migraine sufferers have shown a decreased activity of the respiratory chain enzymes. Studies with phosphorus magnetic resonance spectroscopy (31P-MRS) have demonstrated an impairment of the brain oxidative energy metabolism both during and between migraine attacks. However, molecular genetic studies have not detected specific mitochondrial DNA (mtDNA) mutations in patients with migraine, although other studies suggest that particular genetic markers (i.e. neutral polymorphisms or secondary mtDNA mutations) might be present in some migraine sufferers. Further studies are still needed to clarify if migraine is associated with unidentified mutations on the mtDNA or on nuclear genes that code mitochondrial proteins. In this paper, we review morphological, biochemical, imaging and genetic studies which bear on the hypothesis that migraine may be related to mitochondrial dysfunction at least in some individuals.

Molecular analysis of cluster headache

OBJECTIVES

Cluster headache (CH) is characterized by severe, recurrent, unilateral attacks of extreme intensity and brief duration. Variants in a myriad of genes were studied in sporadic CH patients, often with conflicting results.

METHODS

We studied gene mutations in some candidate genes, hypocretin receptor 2, Clock, and alcohol dehydrogenase 4 (ADH4), in 54 unrelated sporadic CH patients and in 200 controls in 8 kindreds/families that included more affected and nonaffected cases. Furthermore, we performed the whole-genome scanning by comparative genomic hybridization, searching for rearrangements associated with DNA gain or loss in a subset of sporadic and familial CH and control participants.

RESULTS

The analysis of candidate genes revealed that only allele and genotype frequency of the 2 ADH4 mutations resulted significantly between sporadic CH and controls; the same mutations were homozygous in CH patients from 2 families. The comparative genomic hybridization analysis revealed 2 novel rearrangements that involved the intron regions of thyrotropin-releasing hormone-degrading enzyme and neurexin 3 (NRXN3) genes, respectively. The first arrangement was present either in CH or in controls, whereas the second one was specifically found in some sporadic and familial CH cases.

CONCLUSIONS

Our data (although obtained on a small number of cases) confirm the genetic heterogeneity of CH, suggesting that mutations in the ADH4 gene and a novel rearrangement involving NRXN3 gene might be related to CH in a subset of cases.

Vitamin supplementation as possible prophylactic treatment against migraine with aura and menstrual migraine

Migraine is the most common form of headache disorder globally. The etiology of migraine is multifactorial, with genetic components and environmental interactions considered to be the main causal factors. Some researchers postulate that deficits in mitochondrial energy reserves can cause migraine or an increase in homocysteine levels can lead to migraine attacks; therefore, vitamins could play a vital role in migraine prevention. For instance, riboflavin influences mitochondrial dysfunction and prevents migraine. Genes such as flavoenzyme 5,10-methylenetetrahydrofolate reductase (MTHFR), especially the C677T variant, have been associated with elevated plasma levels of homocysteine and migraine with aura. Homocysteine catalyzation requires the presence of vitamins B₆, B₁₂, and folic acid, which can decrease the severity of migraine with aura, making these vitamins potentially useful prophylactic agents for treating migraine with aura. Menstrual migraine, on the other hand, is associated with increased prostaglandin (PG) levels in the endometrium, indicating a role for vitamin E, which is an anti-PG. Vitamin C can also be used as a scavenger of reactive oxygen species for treating neurogenic inflammation in migraine patients. This paper reviews possible therapies based on vitamin supplementation for migraine prophylaxis, focusing on migraine with aura and menstrual migraine.

Cluster headache and the hypocretin receptor 2 reconsidered: A genetic association study and meta-analysis

Background

Cluster headache is a severe neurological disorder with a complex genetic background. A missense single nucleotide polymorphism (rs2653349; p.Ile308Val) in the HCRTR2 gene that encodes the hypocretin receptor 2 is the only genetic factor that is reported to be associated with cluster headache in different studies. However, as there are conflicting results between studies, we re-evaluated its role in cluster headache.

Methods

We performed a genetic association analysis for rs2653349 in our large Leiden University Cluster headache Analysis (LUCA) program study population. Systematic selection of the literature yielded three additional studies comprising five study populations, which were included in our meta-analysis. Data were extracted according to predefined criteria.

Results

A total of 575 cluster headache patients from our LUCA study and 874 controls were genotyped for HCRTR2 SNP rs2653349 but no significant association with cluster headache was found (odds ratio 0.91 (95% confidence intervals 0.75–1.10), p = 0.319). In contrast, the meta-analysis that included in total 1167 cluster headache cases and 1618 controls from the six study populations, which were part of four different studies, showed association of the single nucleotide polymorphism with cluster headache (random effect odds ratio 0.69 (95% confidence intervals 0.53–0.90), p = 0.006). The association became weaker, as the odds ratio increased to 0.80, when the meta-analysis was repeated without the initial single South European study with the largest effect size.

Conclusions

Although we did not find evidence for association of rs2653349 in our LUCA study, which is the largest investigated study population thus far, our meta-analysis provides genetic evidence for a role of HCRTR2 in cluster headache. Regardless, we feel that the association should be interpreted with caution as meta-analyses with individual populations that have limited power have diminished validity.

Mitochondrial dysfunction in migraine

Migraine is the most frequent type of headache in children. In the 1980s, scientists first hypothesized a connection between migraine and mitochondrial (mt) disorders. More recent studies have suggested that at least some subtypes of migraine may be related to a mt defect. Different types of evidence support a relationship between mitochondria (mt) and migraine: (1) Biochemical evidence: Abnormal mt function translates into high intracellular penetration of Ca(2+), excessive production of free radicals, and deficient oxidative phosphorylation, which ultimately causes energy failure in neurons and astrocytes, thus triggering migraine mechanisms, including spreading depression. The mt markers of these events are low activity of superoxide dismutase, activation of cytochrome-c oxidase and nitric oxide, high levels of lactate and pyruvate, and low ratios of phosphocreatine-inorganic phosphate and N-acetylaspartate-choline. (2) Morphologic evidence: mt abnormalities have been shown in migraine sufferers, the most characteristic ones being direct observation in muscle biopsy of ragged red and cytochrome-c oxidase-negative fibers, accumulation of subsarcolemmal mt, and demonstration of giant mt with paracrystalline inclusions. (3) Genetic evidence: Recent studies have identified specific mutations responsible for migraine susceptibility. However, the investigation of the mtDNA mutations found in classic mt disorders (mt encephalomyopathy with lactic acidosis and stroke-like episodes, myoclonus epilepsy with ragged red fibers, Kearns-Sayre syndrome, and Leber hereditary optic neuropathy) has not demonstrated any association. Recently, 2 common mtDNA polymorphisms (16519C→T and 3010G→A) have been associated with pediatric cyclic vomiting syndrome and migraine. Also, POLG mutations (eg, p.T851 A, p.N468D, p.Y831C, p.G517V, and p.P163S) can cause disease through impaired replication of mtDNA, including migraine. Further studies to investigate the relationship between mtDNA and migraine will require very large sample sizes to obtain statistically significant results. (4) Therapeutic evidence: Several agents that have a positive effect on mt metabolism have shown to be effective in the treatment of migraines. The agents include riboflavin (B2), coenzyme Q10, magnesium, niacin, carnitine, topiramate, and lipoic acid. Further study is warranted to learn how mt interact with other factors to cause migraines. This will facilitate the development of new and more specific treatments that will reduce the frequency or severity or both of this disease.

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.

Genetics of cluster headache

Cluster headache (CH) is a rare, excruciating primary headache disorder. A genetic basis has been suggested by family and twin studies, but the mode of transmission seems to vary and the amount of heritability is unclear. The number of genetic association studies investigating variants implicated in the pathophysiology of CH is limited. The HCRTR2 1246G > A and the ADH4 925A > G polymorphisms have been associated with CH. The former has been confirmed and may affect the hypothalamic hypocretin system. However, it only appears to account for a part of the genetic susceptibility for CH, and additional genetic and environmental factors are likely implicated. Pharmacogenetic studies have suggested that the GNB3 825C > T polymorphism may modify treatment response to triptans among CH patients by altering the signal transduction cascade via G protein-coupled receptors. Genetic studies in CH are notoriously difficult due to the complex nature of the disorder and the low prevalence of CH.

Genetic factors in cluster headache

Genetic factors are likely to play a role in cluster headache but are not simply accounted for. A small number of family studies have illustrated the role of genetics, and a few inconclusive studies assessed candidate genes for cluster headache. These clinical genetic studies are reviewed and the author's results from a large database of cluster headache patients are reported. The importance of genetic factors in cluster headache pathophysiology and comment on difficulties in genetic research of cluster headache are discussed.

High frequency of migraine-only patients negative for the 3243 A>G tRNALeu mtDNA mutation in two MELAS families

Migraine is associated with stroke-like episodes in mitochondrial encephalomyopathy, lactic acidosis, stroke-like syndrome (MELAS). Moreover, abnormalities of oxidative phosphorylation are also reported in migraine. We studied two maternal lineages with MELAS and chronic progressive external ophthalmoplegia (CPEO) affected probands carrying the 3243 A>G tRNALeu (MELAS) mutation, remarkable for a high frequency of subjects suffering only migraine. Thus, migraine could be a monosymptomatic expression of the MELAS mutation. We assessed the 3243 A>G tRNALeu mutational load in skeletal muscle and other somatic tissues from the migraine-only subjects, as well as lactic acid levels after exercise. All migraine-only subjects did not carry the MELAS mutation. Muscle biopsy showed mild mitochondrial abnormalities in the non-mutant, migraine-only subjects and, occasionally, abnormal lactic acid. Clear features of mitochondrial myopathy and pathological lactic acid characterised the subjects carrying the MELAS mutation. Our study demonstrates that migraine-only subjects lacked the MELAS mutation, but still had a possible mtDNA-associated genetic predisposition, being maternally related and having some evidence of impaired mitochondrial oxidative phosphorylation.

Genetics of headaches

Insight into the molecular mechanisms involved in primary headaches is important to identify drug targets for improving treatment of patients, but essentially lacking. Genetic research is increasingly successful in pinpointing these mechanisms. Most progress has been made for Familial Hemiplegic Migraine, a rare subtype of migraine with aura. Three genes (CACNA1A, ATP1A2 and SCN1A) have been identified that all encode ion transporters. Cellular and transgenic mouse studies suggest that neuronal hyperexcitability and increased susceptibility to cortical spreading depression, the correlate of migraine aura, are important molecular mechanisms in migraine. Investigating monogenic diseases in which migraine is a prominent feature such as CADASIL, which is caused by mutations in the NOTCH3 gene, can help understanding the pathology of migraine. Candidate gene association studies and linkage studies in the common forms of migraine were less successful. Except for the MTHFR gene no gene variant has been identified yet. Convincingly demonstrated genetic findings in other primary headaches such as cluster headache and tension-type headache are even rarer. However, with current technical possibilities of massive genotyping and international efforts to collect large well-phenotyped patient cohorts, the first gene variants for various primary headache types are likely to be discovered in the coming decade.

The primary headaches: genetics, epigenetics and a behavioural genetic model

The primary headaches, migraine with (MA) and without aura (MO) and cluster headache, all carry a substantial genetic liability. Familial hemiplegic migraine (FHM), an autosomal dominant mendelian disorder classified as a subtype of MA, is due to mutations in genes encoding neural channel subunits. MA/MO are considered multifactorial genetic disorders, and FHM has been proposed as a model for migraine aetiology. However, a review of the genetic studies suggests that the FHM genes are not involved in the typical migraines and that FHM should be considered as a syndromic migraine rather than a subtype of MA. Adopting the concept of syndromic migraine could be useful in understanding migraine pathogenesis. We hypothesise that epigenetic mechanisms play an important role in headache pathogenesis. A behavioural model is proposed, whereby the primary headaches are construed as behaviours, not symptoms, evolutionarily conserved for their adaptive value and engendered out of a genetic repertoire by a network of pattern generators present in the brain and signalling homeostatic imbalance. This behavioural model could be incorporated into migraine genetic research.

Genetic, pathogenetic, and phenotypic implications of the mitochondrial A3243G tRNALeu(UUR) mutation

Mitochondrial disorders are frequently caused by mutations in mitochondrial genes and usually present as multisystem disease. One of the most frequent mitochondrial mutations is the A3,243G transition in the tRNALeu(UUR) gene. The phenotypic expression of the mutation is variable and comprises syndromic or non-syndromic mitochondrial disorders. Among the syndromic manifestations the mitochondrial encephalopathy, lactacidosis, and stroke-like episode (MELAS) syndrome is the most frequent. In single cases the A3,243G mutation may be associated with maternally inherited diabetes and deafness syndrome, myoclonic epilepsy and ragged-red fibers (MERRF) syndrome, MELAS/MERRF overlap syndrome, maternally inherited Leigh syndrome, chronic external ophthalmoplegia, or Kearns-Sayre syndrome. The wide phenotypic variability of the mutation is explained by the peculiarities of the mitochondrial DNA, such as heteroplasmy and mitotic segregation, resulting in different mutation loads in different tissues and family members. Moreover, there is some evidence that additional mtDNA sequence variations (polymorphisms, haplotypes) influence the phenotype of the A3,243G mutation. This review aims to give an overview on the actual knowledge about the genetic, pathogenetic, and phenotypic implications of the A3,243G mtDNA mutation.

The mitochondrial myopathy encephalopathy, lactic acidosis with stroke-like episodes (MELAS) syndrome: a review of treatment options

Mitochondrial encephalomyopathies are a multisystemic group of disorders that are characterised by a wide range of biochemical and genetic mitochondrial defects and variable modes of inheritance. Among this group of disorders, the mitochondrial myopathy, encephalopathy, lactic acidosis with stroke-like episodes (MELAS) syndrome is one of the most frequently occurring, maternally inherited mitochondrial disorders. As the name implies, stroke-like episodes are the defining feature of the MELAS syndrome, often occurring before the age of 15 years. The clinical course of this disorder is highly variable, ranging from asymptomatic, with normal early development, to progressive muscle weakness, lactic acidosis, cognitive dysfunction, seizures, stroke-like episodes, encephalopathy and premature death. This syndrome is associated with a number of point mutations in the mitochondrial DNA, with over 80% of the mutations occurring in the dihydrouridine loop of the mitochondrial transfer RNA(Leu(UUR)) [tRNA(Leu)((UUR))] gene. The pathophysiology of the disease is not completely understood; however, several different mechanisms are proposed to contribute to this disease. These include decreased aminoacylation of mitochondrial tRNA, resulting in decreased mitochondrial protein synthesis; changes in calcium homeostasis; and alterations in nitric oxide metabolism. Currently, no consensus criteria exist for treating the MELAS syndrome or mitochondrial dysfunction in other diseases. Many of the therapeutic strategies used have been adopted as the result of isolated case reports or limited clinical studies that have included a heterogeneous population of patients with the MELAS syndrome, other defects in oxidative phosphorylation or lactic acidosis due to disorders of pyruvate metabolism. Current approaches to the treatment of the MELAS syndrome are based on the use of antioxidants, respiratory chain substrates and cofactors in the form of vitamins; however, no consistent benefits have been observed with these treatments.

Epidemiology and genetics of cluster headache

Cluster headache, the most severe primary headache, is characterised by unilateral pain, ipsilateral autonomic features, and, in many cases, restlessness. Recent epidemiological studies indicate that the prevalence of cluster headache is about one person per 500. Genetic epidemiological surveys indicate that first-degree relatives are five to 18 times-and second-degree relatives, one to three times-more likely to have cluster headache than the general population. Inheritance is likely to be autosomal dominant with low penetrance in some families, although there may also be autosomal recessive or multifactorial inheritance in others. To date, no molecular genetic clues have been identified for cluster headache. Identification of genes for cluster headache is likely to be difficult because most families reported have few affected members and genetic heterogeneity is likely. Future focus should be on ion channel genes and clock genes. This review summarises the epidemiology and genetics of cluster headache.

Leukocyte mitochondrial DNA A to G polymorphism at 11084 is not a risk factor for Japanese migraineurs

Mitochondrial dysfunction has been reported in patients with migraine. We investigated leukocyte mitochondrial DNA 11084 A to G polymorphism in 166 Japanese migraineurs and 483 Japanese controls. The migraine group consisted of 43 patients suffering from migraine with aura (MWA) and 123 from migraine without aura (MOA). The frequency of the transition was 7.2% (12/166) in the migraine group and 7.3% (35/483) in the controls. The frequency of the transition was 4.7% in MWA and 8.1% in MOA. There was no significant difference among the groups (chi-square test). The mitochondrial DNA 11084 A to G transition was more common in Japanese subjects than reported in Caucasians; however, this polymorphism is not a genetic risk factor for migraine in Japanese patients.

No involvement of the calcium channel gene (CACNA1A) in a family with cluster headache

It is very likely that genetic factors play a role in the pathophysiology of cluster headache (CH). As CH shares its paroxysmal character with migraine, and migraine has been described in coexistence with CH in some families, we hypothesized that both diseases might share a genetic aetiology. In this study, we tested whether the migraine CACNA1A gene on chromosome 19 is involved in CH in an extended pedigree. Haplotype analysis did not reveal an obvious disease haplotype, and SSCP analysis of all 47 exons of the CACNA1A gene did not reveal a causative mutation. CH in this family is not caused by mutations in the CACNA1A gene.

Deficient energy metabolism is associated with low free magnesium in the brains of patients with migraine and cluster headache

We used phosphorus magnetic resonance spectroscopy to assess in vivo the brain cytosolic free magnesium concentration and the free energy released by the reaction of adenosine triphosphate (ATP) hydrolysis (DeltaG(ATPhyd)), the latter being an index of the cell's bioenergetics condition. We studied 78 patients with migraine in attack-free periods (7 with migraine stroke, 13 with migraine with prolonged aura, 37 with migraine with typical aura or basilar migraine, and 21 with migraine without aura), and 13 patients with cluster headache. In the occipital lobes of all subgroups of migraine and in cluster headache patients cytosolic free [Mg(2+)] as well as the free energy released by the reaction of ATP hydrolysis were significantly reduced. Among migraine patients, the level of free energy released by the reaction of ATP hydrolysis and the cytosolic free [Mg(2+)] showed a trend in keeping with the severity of clinical phenotype, both showing the lowest values in patients with migraine stroke and the highest in patients with migraine without aura. These results support our current hypothesis that the reduction in free [Mg(2+)] in tissues with mitochondrial dysfunction is secondary to the bioenergetics deficit, and are against a primary role of low brain cytosolic free [Mg(2+)] in causing the bioenergetics deficit in headache.

Hypothalamic involvement and activation in cluster headache

Cluster headache is an episodic form of primary neurovascular headache that is both severe and relatively rare. It is characterized by episodes of headache with cranial parasympathetic activation and sympathetic impairment that come in bouts, or clusters. Its pathophysiology can be divided into understanding the attack phenotype and the biotype of the periodicity. Acute attacks of cluster headache are marked by trigeminal nerve-mediated pain and with cranial autonomic activation, trigeminal-autonomic cephalalgia; an activation that characterizes the phenotype of a group of headaches. The signature feature of cluster headache is its periodicity, the daily cycle of attacks when the patient is in an active bout, or the circumannual, or other period, cycling that distinguishes the on period from the off period. Functional brain imaging with positron emission tomography and structural imaging with voxel-based morphometry have identified an area in the posterior hypothalamic gray as key in understanding cluster headache. This area is subtly enlarged in its gray matter volume, active during an acute cluster headache but inactive when patients are challenged between bouts. Cluster headache is likely to be a form of primary neurovascular pain whose phenotypic expression relies on the trigeminal-autonomic reflex, with a biotype determined by the brain area, the posterior hypothalamus, in which the lesion seems to be located. Understanding both the phenotypic expression and the biotype will, respectively, enable better acute attack treatments and better preventative management of this horrible form of headache.

Heterogeneous presentation in A3243G mutation in the mitochondrial tRNA(Leu(UUR)) gene

AIMS

To clarify the phenotype-genotype relation associated with the A3243G mitochondrial DNA mutation.

METHODS

Five unrelated probands harbouring the A3243G mutation but presenting different clinical phenotype were analysed. Probands include Leigh syndrome (LS(3243)), mitochondrial myopathy, encephalopathy, lactic acidosis and stroke like episodes (MELAS(3243)), progressive external ophthalmoplegia (PEO(3243)), and mitochondrial diabetes mellitus (MDM(3243)). Extensive clinical, histological, biochemical, and molecular genetic studies were performed on five families.

RESULTS

All patients showed ragged red fibres (RRF), and focal cytochrome c oxidase (COX) deficiency except for the patient with MDM(3243). The mutation load was highest in the proband with LS(3243) (>90%), who also presented the highest proportion of RRF (68%) and COX negative fibres (10%), and severe complex I plus IV deficiency. These proportions were lower in the probands with PEO(3243) and with MDM(3243).

CONCLUSION

The most severe clinical phenotype, LS(3243), was associated with the highest proportion of the A3243G mutation as well as the most prominent histological and biochemical abnormalities.

Molecular genetics of migraine headaches: a review

Following the recent discovery of neural calcium channel mutations in familial hemiplegic migraine, genetic linkage and association studies have been performed world-wide in an effort to unveil the genetic basis of the more common types of migraine too. Mutations in neural calcium channels, mitochondrial DNA, serotonin receptors and transporter, dopamine receptors and genetic prothrombotic risk factors have been especially investigated and are discussed here. No unambiguous conclusions have, however, been reached. FHM remains an isolated success story in the quest for the genetic basis of migraine.

Current status of genetic discoveries in migraine: familial hemiplegic migraine and beyond

Familial hemiplegic migraine (FHM) has been related to mutations in a brain calcium channel gene among Chr19p linked FHM families. Subsequent genetic Studies in different FHM families showed that additional causative genes must reside in other regions of the genome, including the long arm of Chromosome 1. Parallel discoveries in mouse mutants involving ion channel genes have also accelerated our understanding of the spectrum and functional significance of the CNS-related ion channel disorders. These studies have clear implications for migraine, epilepsy, and ataxia. An association study was suggested that other 'susceptibility' genes like the dopamine DRD2 receptor will be important in characterizing the genetic components of the larger, heterogeneous group of migraine disorders.

Cluster headache: imaging and other developments

Cluster headache, one of the most severe pain syndromes in humans, is usually described as a vascular headache. However, the striking circadian rhythmicity of this strictly unilateral pain syndrome cannot readily be explained by the vascular hypothesis. Recent studies using positron emission tomography suggest that a central nervous system dysfunction in the region of the hypothalamus is the primum movens in the pathophysiology of cluster headache. From a physiological viewpoint, therefore, cluster headache should be described as a neurovascular headache, thus placing equal emphasis on its fundamental pathophysiology and clinical expression.

Quantitative analysis of skeletal muscle bioenergetics and proton efflux in migraine and cluster headache

Phosphorus MR spectroscopy (31P-MRS) was used to quantify skeletal muscle bioenergetics and proton efflux in 63 patients with migraine (23 with migraine without aura, MwoA, 22 with migraine with aura, MwA, and 18 with prolonged aura or stroke, CM) and in 14 patients with cluster headache (CH), all in an attack-free period. At rest mitochondrial function was abnormal only in CM, as shown by a low phosphocreatine (PCr) concentration. At the end of a mixed glycolytic/aerobic exercise all three migraine groups showed a significantly smaller decrease of cytosolic pH compared to controls with a similar end-exercise PCr breakdown, while end-exercise pH was normal in cluster headache patients. The normal rate of proton efflux in all headache groups suggests that the reduced end-exercise acidification was due to a reduction of glycolytic flux in migraine patients. The maximum rate of mitochondrial ATP production (Qmax), calculated from the rate of post-exercise PCr recovery and the end-exercise [ADP], was low in cluster headache patients as well as in migraine patients except MwoA. In migraine the degree of the mitochondrial impairment, that apparently is associated with a reduced glycolytic flux, is related to the severity of the clinical phenotype.

Genetics of migraine

Although family studies and twin studies are not sufficiently reliable to establish this theory with certainty, migraine likely is influenced by hereditary susceptibility. The association of migraine with a large number of hereditary diseases opens the possibility to choose candidate chromosomes for linkage studies. A rare subtype of migraine, familial hemiplegic migraine, is linked to chromosome 19p and at least one other locus. The chromosome 19p also seems to be involved in "normal" migraine, although conflicting results have been reported.

Investigation on the mitochondrial transfer RNA(Leu)(UUR) in blood cells from patients with cluster headache

Various mutations in the mitochondrial tRNA(Leu)(UUR) gene give rise to a variety of neurological disorders. Among these, mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS syndrome) are frequently associated with a tRNA(Leu)(UUR) mutation at nucleotide position 3243 of the mitochondrial DNA. A supplementary clinical feature seen in these patients is headache in early life. Recently, a tRNA(Leu)(UUR) mutation at nucleotide position 3243 has been found in a patient presenting with cluster headache. This led us to examine the mitochondrial genomes of 22 patients presenting with cluster headache. None of the patients harboured the reported tRNA(Leu)(UUR) mutation or any other length variations of the mtDNA. Cluster headache is most likely not causally associated with the A3243G mutation of the mitochondrial DNA.