Increased risk of sensorineural hearing loss and migraine in patients with a rare mitochondrial DNA variant 4336A>G in tRNAGln

Genetics of migraine: where are we now?

Migraine is a complex brain disorder explained by the interaction of genetic and environmental factors. In monogenic migraines, including familial hemiplegic migraine and migraine with aura associated with hereditary small-vessel disorders, the identified genes code for proteins expressed in neurons, glial cells, or vessels, all of which increase susceptibility to cortical spreading depression. The study of monogenic migraines has shown that the neurovascular unit plays a prominent role in migraine. Genome-wide association studies have identified numerous susceptibility variants that each result in only a small increase in overall migraine risk. The more than 180 known variants belong to several complex networks of "pro-migraine" molecular abnormalities, which are mainly neuronal or vascular. Genetics has also highlighted the importance of shared genetic factors between migraine and its major co-morbidities, including depression and high blood pressure. Further studies are still needed to map all of the susceptibility loci for migraine and then to understand how these genomic variants lead to migraine cell phenotypes.

Abnormal Subjective and Audiometric Auditory Function in Migraine

OBJECTIVE

To identify if migraine is associated with auditory deficits and if the auditory profile of migraine is distinct from other pain syndromes, such as chronic pain.

STUDY DESIGN

Cross-sectional, retrospective.

SETTING

A total of 5273 respondents of the 1999 to 2004 National Health and Nutrition Examination Survey.

METHODS

Regression analyses assessed the association between migraine (n = 1245) and chronic pain (n = 430) status with subjectively endorsed hearing loss, tinnitus, pure-tone average (PTA) at 500, 1000, 2000, and 4000 Hz, and subjective-audiometric hearing mismatch (endorsed hearing loss but with a PTA ≤ 25 dB), correcting for confounding factors.

RESULTS

Migraine was associated with increased tinnitus (adjusted odds ratio [aOR] = 1.77, 95% confidence interval [CI]: 1.47-2.13, p < .001) and subjective hearing loss (aOR = 1.58, 95% CI: 1.29-1.94, p < .001). Migraine was associated with higher PTA (β = .89, p = .023). Migraine decreased the PTA threshold at which individuals endorsed subjective hearing loss (β = -1.94, p = .013) and was associated with a more subjective-audiometric hearing mismatch (aOR = 1.50, 95% CI: 1.18-1.89, p < .001). Chronic pain was not associated with tinnitus (aOR = 1.26, 95% CI: 0.97-1.63, p = 0.079), subjective hearing loss (aOR = 0.94, 95% CI: 0.71-1.23, p = .64), changes in PTA (β = -.22, p = .69), altered PTA threshold for endorsing hearing loss (β = 1.40, p = .19), or subjective-audiometric hearing mismatch (aOR = 0.98, 95% CI: 0.70-1.34, p = .88).

CONCLUSION

Migraine is associated with both worse pure-tone audiometry and higher sensitivity to changes in hearing ability, suggesting both peripheral and central auditory function abnormalities. In contrast, patients with chronic pain did not demonstrate these abnormalities. The etiology of abnormal auditory processing in migraine may be different from that of other pain syndromes.

A Pilot Mitochondrial Genome-Wide Association on Migraine Among Saudi Arabians

Background

Mitochondrial DNA (mtDNA) mutations have been reported in multiple neurological diseases and helped to explain the pathophysiology of these diseases. Similarly, variations in mtDNA might exist in migraine and can explain the effect of low ATP production in the neurons on the initiation of migraine attack. Therefore, in the current study we aim to explore the association of mtDNA mutations on migraine in the Saudi population.

Subjects and Methods

Over 1950 young Saudi female students were screened for migraine, among that a total of 103 satisfied the ICHD-3 criteria. However,  20 migraine cases confirmed in the neurology clinic and gave consent to participate in the study. Another 20 age-matched healthy controls were also recruited. Mitochondrial sequence variations were filtered from exome sequencing using NCBI GenBank Reference Sequence: NC_012920.1 and analysed using MITOMAP. Genes with significant single nucleotide polymorphisms (SNPs) were investigated by the gene functional classification tool DAVID and functional enrichment analysis of protein-protein interaction networks through STRING 11.5 for the most significant associated genes.

Results

Genome wide analysis of the mitochondrial sequence variations between the patients with migraine and control revealed the association of 30 SNPs (p < 0.05) in the mitochondrial genome. The highest significance (p = 0.001033) was observed in a coding SNP (rs1603225278) in the CYTB gene and rs386829281 in the region of origin of replication. Twenty-four significant SNPs were in the coding region of nine (ND5, ND4, COX2, COX1, ND3, CYTB, COX3, ND2 and ND1) genes.

Conclusion

This is the first study to demonstrate the association of mtDNA variations with migraine in the Saudi population. The current findings will help to highlight the significance of mtDNA mutations to migraine pathophysiology and will serve as a reference data for larger national and international studies.

Clinical use of NGS data from the targeted gene panel for mitochondrial diseases screening

BACKGROUND AND OBJECTIVE

Mitochondrial diseases are a frequent cause of inherited genetic disorders caused by mutations in both the mitochondrial and nuclear human genome. The new technique of high-throughput sequencing, which is used more and more frequently around the world, is most often focused on nuclear DNA. In some cases, such data after proper IT processing could also allow to determine alterations in mtDNA genome. In our work, we want to verify that off-target reads from targeted gene panels are sufficient data to determine pathogenic variants in the mitochondrial genome.

METHODS

We analyzed 50 patients who underwent routine diagnostics with the Illumina's TruSight One Sequencing Panel. In the entire bioinformatic analysis process, we have used only free, user-friendly and generally available online tools that do not require specialized IT knowledge.

RESULTS

Most of the data obtained were suitable for determining the presence of homoplasmic variants in mtDNA; 84% of the data met the minimum 20-fold coverage requirement as defined in the scientific literature for clinical data. We managed to identify 16 pathogenic variants in the examined genetic material (mtDNA) according to the ClinVar database.

CONCLUSIONS

In conclusion, we have outlined that off-target reads from targeted gene panel (TruSight One Sequencing Panel) may also be suitable for determining potentially pathogenic homoplasmic variants in mtDNA. We also described a simple pipeline based only on free tools available online. Introducing such a pipeline into a standard procedure of clinical units which carry out such research undoubtedly can extend the diagnostic potential by information about mtDNA, especially when it is based on purely free tools that do not require specialized bioinformatic knowledge.

Mitochondrial genome-wide association study of migraine - the HUNT Study

BACKGROUND

Variation in mitochondrial DNA (mtDNA) has been indicated in migraine pathogenesis, but genetic studies to date have focused on candidate variants, with sparse findings. We aimed to perform the first mitochondrial genome-wide association study of migraine, examining both single variants and mitochondrial haplogroups.

METHODS

In total, 71,860 participants from the population-based Nord-Trøndelag Health Study were genotyped. We excluded samples not passing quality control for nuclear genotypes, in addition to samples with low call rate and closely maternally related. We analysed 775 mitochondrial DNA variants in 4021 migraine cases and 14,288 headache-free controls, using logistic regression. In addition, we analysed 3831 cases and 13,584 controls who could be reliably assigned to a mitochondrial haplogroup. Lastly, we attempted to replicate previously reported mitochondrial DNA candidate variants.

RESULTS

Neither of the mitochondrial variants or haplogroups were associated with migraine. In addition, none of the previously reported mtDNA candidate variants replicated in our data.

CONCLUSIONS

Our findings do not support a major role of mitochondrial genetic variation in migraine pathophysiology, but a larger sample is needed to detect rare variants and future studies should also examine heteroplasmic variation, epigenetic changes and copy-number variation.

Mitochondria in migraine pathophysiology - does epigenetics play a role?

The approximately three times higher rate of migraine prevalence in women than men may result from the mitochondrial transmission of this disease. Studies with imaging techniques suggest disturbances in mitochondrial metabolism in specific regions of the brain in migraine patients. Migraine shares some clinical features with several mitochondrial diseases and many other disorders include migraine headaches. Epigenetic regulation of mitochondrial DNA (mtDNA) is a matter of debate and there are some conflicting results, especially on mtDNA methylation. Micro RNAs (miRNAs) and long-noncoding RNA (lncRNAs) have been detected in mitochondria. The regulation of the miRNA-lncRNA axis can be important for mitochondrial physiology and its impairment can result in a disease phenotype. Further studies on the role of mitochondrial epigenetic modifications in migraine are needed, but they require new methods and approaches.

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.

Detection of mitochondrial transfer RNA (mt-tRNA) gene mutations in patients with idiopathic pulmonary fibrosis and sarcoidosis

Mitochondrial reactive oxygen species production may lead to tissue injury associated with two respiratory disorders of unknown origin which are shared by common tissue fibrosis, IPF and sarcoidosis. Sequence analysis of 22 mt-tRNA genes and parts of their flanking genes revealed 32 and 45 mutations in 38/40 IPF and 69/85 sarcoidosis patients respectively. 4 novel mutations were identified. 15/32 and 25/45 mutations were exclusively expressed while 12/32 and 17/45 mutations predominantly occurred in IPF and sarcoidosis group respectively, compared to healthy controls. Novel mutation combinations were solely expressed in disease. Hence, a mitochondrial-mediated pathogenic pathway seems to underlie both entities.

Gene-centric analysis implicates nuclear encoded mitochondrial protein gene variants in migraine susceptibility

Background

Migraine is a common neurological disorder which affects a large proportion of the population. The Norfolk Island population is a genetically isolated population and is an ideal discovery cohort for genetic variants involved in complex disease susceptibility given the reduced genetic and environmental heterogeneity. Given that the majority of proteins responsible for mitochondrial function are nuclear encoded, this study aimed to investigate the role of Nuclear Encoded Mitochondrial Protein (NEMP) genes in relation to migraine susceptibility.

Methods

A gene‐centric association analysis of NEMP genes was undertaken in the most related individuals (n = 315) within the genetically isolated Norfolk Island population. The discovery phase included genes with three or more SNP associations (P < 0.005), which were investigated further in a replication phase using an unrelated migraine case–control cohort (544 patients and 584 controls).

Results

The discovery phase of the study implicated SNPs in 5 NEMP genes to be associated with migraine susceptibility (P < 0.005). Replication analysis validated some of these implicated genes with SNPs in three NEMP genes shown to be associated with migraine in the replication cohort. These were CSNK1G3 (P = 0.00037), ELOVL6 (P = 0.00035) and SARDH (P = 0.00081), which are involved in phosphorylation, fatty acid metabolism, and oxidative demethylation, respectively.

Conclusion

Here we provide evidence that variation in NEMP genes is associated with migraine susceptibility. This study provides evidence for a link between mitochondrial function and migraine susceptibility.

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.

No evidence of association between common European mitochondrial DNA variants in Alzheimer, Parkinson, and migraine in the Spanish population

Certain mitochondrial DNA (mtDNA) variants and haplogroups have been found to be associated with neurological disorders. Several studies have suggested that mtDNA variation could have an etiologic role in these disorders by affecting the ATP production on high-energy demanding organs, such as the brain. We have analyzed 15 mtDNA SNPs (mtSNPs) in five cohorts of cases presenting Alzheimer disease (AD), Parkinson disease (PD), and migraine, and in controls, to evaluate the role mtDNA variation in disease risk. Association tests were undertaken both for mtSNPs and mitochondrial haplogroups. No significant association was detected for any mtSNP or haplogroup in AD and PD cohorts. Two mtSNPs were associated with one migraine cohort after correcting for multiple tests, namely, T4216C and G13708A and haplogroup J (FDR q-value = 0.02; Santiago's cohort). However, this association was not confirmed in a second replication migraine series. A review of the literature reveals the existence of inconsistent findings and methodological shortcomings affecting a large proportion of mtDNA association studies on AD, PD, and migraine. A detailed inspection of the literature highlights the need for performing more rigorous methodological and statistical standards in mtDNA genetic association studies aimed to avoid false positive results of association between mtDNA variants and neurological diseases.

CoEnzyme Q10 and riboflavin: the mitochondrial connection

OBJECTIVE

We conducted a short review of relevant literature which contends that migraine is associated with a wide-spread metabolic abnormality of mitochondrial oxidative metabolism, leading to the use of riboflavin and coenzyme Q10 as prophylactic therapy for migraine.

BACKGROUND

Riboflavin and coenzyme Q10 supplementation has been recommended widely as safe and effective prophylactic therapy for migraine. The background neurophysiological studies that led to the development of this therapy, which are extremely complex, deserve wider distribution.

METHODS

A brief review of the relevant literature was conducted and summarized.

RESULTS

Brain energy metabolism in migraine has been found to be abnormal in all types of migraine, making the migrainous brain hyper-responsive to many stimuli. The metabolic abnormalities are more severe in the more-severe types of migraine, such as hemiplegic migraine and migrainous stroke, but they are present both during and between attacks. The metabolic abnormality in migraine extends beyond the brain to platelets and muscles, as proven by techniques of biochemistry, muscle morphology, and nuclear magnetic spectroscopy. There are strong similarities between migraine and certain inborn errors of metabolism, the metabolic encephalomyopathies, in which patients suffer genetic abnormalities in mitochondrial energy production to produce lactic acidosis, stroke, and migraine headaches. The theory of migraine as a mitochondrial disorder seems to have abundant evidence. However, aside from the genetic abnormalities discovered for the familial hemiplegic migraines, molecular genetic studies in migraine have been negative until recently, when whole genome sequencing has now reported positive results.

CONCLUSION

Arising from these extensive neurophysiological studies, the treatment of metabolic encephalomyopathies with pharmacological doses of riboflavin and coenzyme Q10 has shown positive benefits. The same treatment has now been applied to migraine, adding clinical support to the theory that migraine is a mitochondrial disorder.

Mitochondrial tRNA mutations associated with deafness

Mitochondrial tRNA mutations are one of the important causes of both syndromic and non-syndromic deafness. Of those, syndromic deafness-associated tRNA mutations such as tRNA(Leu(UUR)) 3243A>G are often present in heteroplasmy, while non-syndromic deafness-associated tRNA mutations including tRNA(Ser(UCN)) 7445A>G often occur in homplasmy or in high levels of heteroplasmy. These tRNA mutations are the primary mutations leading to hearing loss. However, other tRNA mutations such as tRNA(Thr) 15927G>A and tRNA(Ser(UCN)) 7444G>A may act in synergy with the primary mitochondrial DNA mutations, modulating the phenotypic manifestation of the primary mitochondrial DNA mutations. Theses tRNA mutations cause structural and functional alteration. A failure in tRNA metabolism caused by these tRNA mutations impaired mitochondrial translation and respiration, thereby causing mitochondrial dysfunctions responsible for deafness. These data offer valuable information for the early diagnosis, management and treatment of maternally inherited deafness.

Human mitochondrial transfer RNAs: role of pathogenic mutation in disease

The human mitochondrial genome encodes 13 proteins. All are subunits of the respiratory chain complexes involved in energy metabolism. These proteins are translated by a set of 22 mitochondrial transfer RNAs (tRNAs) that are required for codon reading. Human mitochondrial tRNA genes are hotspots for pathogenic mutations and have attracted interest over the last two decades with the rapid discovery of point mutations associated with a vast array of neuromuscular disorders and diverse clinical phenotypes. In this review, we use a scoring system to determine the pathogenicity of the mutations and summarize the current knowledge of structure-function relationships of these mutant tRNAs. We also provide readers with an overview of a large variety of mechanisms by which mutations may affect the mitochondrial translation machinery and cause disease.

Mitochondrial Genetic Background Modifies Breast Cancer Risk

Inefficient mitochondrial electron transport chain (ETC) function has been implicated in the vicious cycle of reactive oxygen species (ROS) production that may predispose an individual to late onset diseases, such as diabetes, hypertension, and cancer. Mitochondrial DNA (mtDNA) variations may affect the efficiency of ETC and ROS production, thus contributing to cancer risk. To test this hypothesis, we genotyped 69 mtDNA variations in 156 unrelated European-American females with familial breast cancer and 260 age-matched European-American female controls. Fisher's exact test was done for each single-nucleotide polymorphism (SNP)/haplogroup and the P values were adjusted for multiple testing using permutation. Odds ratio (OR) and its 95% confidence interval (95% CI) were calculated using the Sheehe correction. Among the 69 variations, 29 were detected in the study subjects. Three SNPs, G9055A (OR, 3.03; 95% CI, 1.63-5.63; P = 0.0004, adjusted P = 0.0057), A10398G (OR, 1.79; 95% CI, 1.14-2.81; P = 0.01, adjusted P = 0.19), and T16519C (OR, 1.98; 95% CI, 1.25-3.12; P = 0.0030, adjusted P = 0.0366), were found to increase breast cancer risk; whereas T3197C (OR, 0.31; 95% CI, 0.13-0.75; P = 0.0043, adjusted P = 0.0526) and G13708A (OR, 0.47; 95% CI, 0.24-0.92; P = 0.022, adjusted P = 0.267) were found to decrease breast cancer risk. Overall, individuals classified as haplogroup K show a significant increase in the risk of developing breast cancer (OR, 3.03; 95% CI, 1.63-5.63; P = 0.0004, adjusted P = 0.0057), whereas individuals bearing haplogroup U have a significant decrease in breast cancer risk (OR, 0.37; 95% CI, 0.19-0.73; P = 0.0023, adjusted P = 0.03). Our results suggest that mitochondrial genetic background plays a role in modifying an individual's risk to breast cancer.

Evidence for adaptive selection acting on the tRNA and rRNA genes of human mitochondrial DNA

In order to identify putative adaptive human mitochondrial DNA (mtDNA), transfer RNA (tRNA), and ribosomal RNA (rRNA) variants, we assembled a sequential mutational tree from 2,460 human mtDNA coding sequences, thus providing the relative age of all mtDNA sequence variants. Deleterious mutations affect evolutionarily conserved nucleotides and have been eliminated from the older internal branches of the tree by purifying selection, while beneficial mutations also alter conserved nucleotides but have been enriched in the internal branches of the tree by adaptive selection. Neutral polymorphisms alter poorly conserved nucleotides and are distributed throughout the tree. Stem nucleotides are more constrained than loop nucleotides. The functional importance of both types of nucleotide variants was assessed by comparison to the average evolutionary conservation index (CI) of all known pathogenic tRNA mutations, thus permitting discrimination between internal branch neutral and adaptive tRNA variants. This revealed that 19% of the stem and 13% of the loop internal branch tRNA variants were potentially adaptive. Since few pathogenic rRNA mutations are known, evidence for adaptive rRNA variation was revealed by higher stem to loop variant ratios and elevated CIs in the internal branches vs. external branches. Moreover, variants among stem noncanonical apposition bases predominantly created new Watson-Crick (WC) base pairs, thus also suggesting adaptive selection. Among the putative adaptive tRNA and rRNA polymorphisms, a number were found to occur at the base of the branches of the tree, to have recurred multiple times, and to be associated with altered human phenotypes. Therefore, a significant portion of ancient tRNA and rRNA polymorphisms appear to have been adaptive, and these are affecting human health today.

Auditory brainstem response in pediatric migraine: during the attack and asymptomatic period

OBJECTIVE

The aim of this study was to evaluate the hearing parameters of children with migraine during ictal and interictal period.

METHOD

16 pediatric patients with migraine and normal otolaryngologic examination were evaluated. Hearing parameters were assessed with auditory brainstem response (ABR) testing between and during the migraine attacks. Binaural absolute latencies of waves I, III and V, interpeak latencies I-III, III-V and I-V of ABR in response to 80 dB nHL clicks were calculated. Initial findings were compared with those of 20 healthy volunteers.

RESULTS

Peak latencies of wave V and interpeak latencies of I-V were prolonged during the attack in migraineurs on the left. The side of latency elongation was not affected by the side of headache. When these parameters were separately compared for gender, they were prolonged in boys during the attack in migraineurs; however in girls, while there was statistically significant difference at interpeak latencies of I-V, no significant difference was noted at peak latencies of wave V.

CONCLUSIONS

ABR waves did not exceed clinical norms in migraine patients in headache-free period. But, important effects on sensorineural hearing parameters were detected during the attack. Our results indicated a transient impairment of the auditory brainstem function during the headache in pediatric migraine patients.

Mitochondrial DNA mutations in patients with postlingual, nonsyndromic hearing impairment

Mitochondrial mutations have previously been reported anecdotally in families with maternally inherited, nonsyndromic hearing impairment. To ascertain the contribution of mitochondrial mutations to postlingual but early-onset, nonsyndromic hearing impairment, we screened patients collected from within two different populations (southern Italy and UK) for previously reported mtDNA mutations associated with hearing disorders. Primer extension (SNP analysis) was used to screen for specific mutations, revealing cases of heteroplasmy and its extent. The most frequently implicated tRNA genes, Leu(UUR) and Ser(UCN), were also sequenced in all Italian patients. All tRNA genes were sequenced in those UK patients showing the clearest likelihood of maternal inheritance. Causative mtDNA mutations were found in approximately 5% of patients in both populations, representing almost 10% of cases that were clearly familial. Age of onset, where known, was generally before adulthood, and hearing loss was typically progressive. Haplogroup analysis revealed a possible excess of haplogroup cluster HV in the patients, compared with population controls, but of borderline statistical significance. In contrast, we did not find any of the previously reported mtDNA mutations, nor a significant deviation from haplogroup cluster frequencies typical of the control population, in patients with late adult-onset hearing loss (age-related hearing impairment) from the UK or Finland.

Study of Mitochondrial DNA Mutations in Patients With Migraine With Prolonged Aura

Ten patients with migraine with prolonged aura were studied for the presence of mitochondrial DNA point mutations utilizing DNA isolated from blood and hair samples. We analyzed for nine point mutations reported in patients with MELAS (A3243G, C3256T, T3271C, T3291C, A5814G, T8356C, T9957C, G13513A, and A13514G) and three secondary LHON mutations (T4216C, A4917G, and G13708A). None of the patients tested had any of these mutations in mitochondrial DNA. However, one patient was found to have a tRNA(Gln) A4336G mitochondrial DNA variant. From this study it appears that migraine with prolonged aura is not an oligosymptomatic form of MELAS and is not related to secondary LHON mutations. The significance of the tRNA A4336G variant is unknown.