A 3-year clinical follow-up of adult patients with 3243A>G in mitochondrial DNA

A platform to map the mind-mitochondria connection and the hallmarks of psychobiology: the MiSBIE study

Health emerges from coordinated psychobiological processes powered by mitochondrial energy transformation. But how do mitochondria regulate the multisystem responses that shape resilience and disease risk across the lifespan? The Mitochondrial Stress, Brain Imaging, and Epigenetics (MiSBIE) study was established to address this question and determine how mitochondria influence the interconnected neuroendocrine, immune, metabolic, cardiovascular, cognitive, and emotional systems among individuals spanning the spectrum of mitochondrial energy transformation capacity, including participants with rare mitochondrial DNA (mtDNA) lesions causing mitochondrial diseases (MitoDs). This interdisciplinary effort is expected to generate new insights into the pathophysiology of MitoDs, provide a foundation to develop novel biomarkers of human health, and integrate our fragmented knowledge of bioenergetic, brain-body, and mind-mitochondria processes relevant to medicine and public health.

Clinical drivers of hospitalisation in patients with mitochondrial diseases

Background

Mitochondrial diseases in adults are generally chronic conditions with a wide spectrum of severity contributing to disease burden and healthcare resource utilisation. Data on healthcare resource utilisation in mitochondrial diseases are limited.

Objectives

We performed a retrospective longitudinal study to investigate the clinical drivers of hospitalisation in adult patients with mitochondrial diseases to better understand healthcare resource utilisation.

Methods

We recruited participants from our specialised Mitochondrial Disease Clinic in Sydney, Australia between September 2018 and December 2021. We performed a retrospective chart review for the period 2013-2022 considering emergency department (ED) and/or hospital admission notes, as well as discharge summaries. We used multiple linear regression models to examine the association between the type of presenting symptom(s) and duration of hospital stay and frequency of admissions, while adjusting for relevant covariates.

Results

Of the 99 patients considered, the duration of hospitalisation ranged from 0 to 116 days per participant and the number of admissions ranged from 0 to 21 per participant. Participants with one or more mitochondrial disease-associated admissions constituted 52% of the study cohort. 13% of the participants presented to the ED without requiring an admission and 35% never attended the ED or required a hospital admission during this period. Neurological (p<0.0001), gastroenterological (p=0.01) and symptoms categorised as 'other' (p<0.0001) were the main presentations driving the total number of days admitted to hospital. A statistically significant association was evident for the number of admissions and all types of presenting symptoms (p<0.0001).

Conclusion

There are variable reasons for hospitalisation in adults with mitochondrial diseases, with neurological and gastroenterological presentations being associated with prolonged and complex hospitalisation. A better understanding of clinical drivers such as these allows for better informed and well-coordinated management aimed at optimising healthcare resource utilisation.

Long-Term Safety of Systemic Ozone Therapy in a Patient With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS)

A patient with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, a rare mitochondrial disease characterized by myopathy, epilepsy, encephalopathy, acidosis, and recurrent cerebral ischemic episodes, underwent systemic hematogenous ozone therapy for 17 years. Despite advancements in the study of mitochondrial diseases, there are currently no available treatments for MELAS. The patient in this case has received over 280 sessions of systemic hematic ozone therapy since 2003 (from the age of 10 years) till the time of publication, without reporting any adverse effects, achieving a normal level of development considering the comorbidities. Possible mechanisms of action of systemic hematogenous ozone therapy include improved efficiency of the mitochondrial oxidative chain through the induction of antioxidant enzymes (catalase, superoxide dismutases {SOD}, peroxidase). More studies are needed to evaluate the actual safety of long-term systemic hematogenous ozone therapy in patients with mitochondrial diseases.

Cognitive Impairment in Primary and Secondary Headache Disorders

Purpose of Review

To critically evaluate the recent literature on cognitive impairment and headache.

Recent Findings

Neurocognitive symptoms are prevalent, debilitating, and occur often with both primary and secondary headache disorders.

Summary

This is a “narrative review of the current literature in PubMed on cognitive function and headache.” Migraine is associated with cognitive impairment years before a migraine diagnosis. In young and middle-aged adults, migraine is associated with deficits in attention, executive function, processing speed, and memory. It is unlikely that migraine is associated with dementia. Although methodologically difficult to assess, there does not seem to be an association between tension-type headache and cognitive dysfunction. In early to midlife, cluster headache seems to be associated with executive dysfunction. Several secondary headache syndromes relevant to clinicians managing headache disorders are associated with poorer cognitive performance or distinctive cognitive patterns, including those attributed to chronic cerebral or systemic vascular disorders, trauma, and derangements of intracranial pressure and volume, including frontotemporal brain sagging syndrome.

Molecular biomarkers correlate with brain grey and white matter changes in patients with mitochondrial m.3243A > G mutation

INTRODUCTION

The mitochondrial DNA (mtDNA) m.3243A > G mutation in the MT-TL1 gene results in a multi-systemic disease, that is commonly associated with neurodegenerative changes in the brain.

METHODS

Seventeen patients harboring the m3243A > G mutation were enrolled (age 43.1 ± 11.4 years, 10 M/7F). A panel of plasma biomarkers including lactate acid, alanine, L-arginine, fibroblast growth factor 21 (FGF-21), growth/differentiation factor 15 (GDF-15) and circulating cell free -mtDNA (ccf-mtDNA), as well as blood, urine and muscle mtDNA heteroplasmy were evaluated. Patients also underwent a brain standardized MR protocol that included volumetric T1-weighted images and diffusion-weighted MRI. Twenty sex- and age-matched healthy controls were included. Voxel-wise analysis was performed on T1-weighted and diffusion imaging, respectively with VBM (voxel-based morphometry) and TBSS (Tract-based Spatial Statistics). Ventricular lactate was also evaluated by ¹H-MR spectroscopy.

RESULTS

A widespread cortical gray matter (GM) loss was observed, more severe (p < 0.001) in the bilateral calcarine, insular, frontal and parietal cortex, along with infratentorial cerebellar cortex. High urine mtDNA mutation load, high levels of plasma lactate and alanine, low levels of plasma arginine, high levels of serum FGF-21 and ventricular lactate accumulation significantly (p < 0.05) correlated with the reduced brain GM density. Widespread microstructural alterations were highlighted in the white matter, significantly (p < 0.05) correlated with plasma alanine and arginine levels, with mtDNA mutation load in urine, with high level of serum GDF-15 and with high content of plasma ccf-mtDNA.

CONCLUSIONS

Our results suggest that the synergy of two pathogenic mechanisms, mtDNA-related mitochondrial respiratory deficiency and defective nitric oxide metabolism, contributes to the brain neurodegeneration in m.3243A > G patients.

Cognitive functioning and mental health in mitochondrial disease: A systematic scoping review

Mitochondrial diseases (MDs) are rare, heterogeneous, hereditary and progressive in nature. In addition to the serious somatic symptoms, patients with MD also experience problems regarding their cognitive functioning and mental health. We provide an overview of all published studies reporting on any aspect of cognitive functioning and/or mental health in patients with MD and their relatives. A total of 58 research articles and 45 case studies were included and critically reviewed. Cognitive impairments in multiple domains were reported. Mental disorders were frequently reported, especially depression and anxiety. Furthermore, most studies showed impairments in self-reported psychological functioning and high prevalence of mental health problems in (matrilineal) relatives. The included studies showed heterogeneity regarding patient samples, measurement instruments and reference groups, making comparisons cautious. Results highlight a high prevalence of cognitive impairments and mental disorders in patients with MD. Recommendations for further research as well as tailored patientcare with standardized follow-up are provided. Key gaps in the literature are identified, of which studies on natural history are of highest importance.

Molecular Epidemiology of Mitochondrial Cardiomyopathy: A Search Among Mitochondrial and Nuclear Genes

Mitochondrial Cardiomyopathy (MCM) is a common manifestation of multi-organ Mitochondrial Diseases (MDs), occasionally present in non-syndromic cases. Diagnosis of MCM is complex because of wide clinical and genetic heterogeneity and requires medical, laboratory, and neuroimaging investigations. Currently, the molecular screening for MCM is fundamental part of MDs management and allows achieving the definitive diagnosis. In this article, we review the current genetic knowledge associated with MDs, focusing on diagnosis of MCM and MDs showing cardiac involvement. We searched for publications on mitochondrial and nuclear genes involved in MCM, mainly focusing on genetic screening based on targeted gene panels for the molecular diagnosis of the MCM, by using Next Generation Sequencing. Here we report twelve case reports, four case-control studies, eleven retrospective studies, and two prospective studies, for a total of twenty-nine papers concerning the evaluation of cardiac manifestations in mitochondrial diseases. From the analysis of published causal mutations, we identified 130 genes to be associated with mitochondrial heart diseases. A large proportion of these genes (34.3%) encode for key proteins involved in the oxidative phosphorylation system (OXPHOS), either as directly OXPHOS subunits (22.8%), and as OXPHOS assembly factors (11.5%). Mutations in several mitochondrial tRNA genes have been also reported in multi-organ or isolated MCM (15.3%). This review highlights the main disease-genes, identified by extensive genetic analysis, which could be included as target genes in next generation panels for the molecular diagnosis of patients with clinical suspect of mitochondrial cardiomyopathies.

Brain MRS correlates with mitochondrial dysfunction biomarkers in MELAS-associated mtDNA mutations

Objective

The purpose of this study was to investigate correlations between brain proton magnetic resonance spectroscopy (¹H‐MRS) findings with serum biomarkers and heteroplasmy of mitochondrial DNA (mtDNA) mutations. This study enrolled patients carrying mtDNA mutations associated with Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke‐like episodes (MELAS), and MELAS‐Spectrum Syndrome (MSS).

Methods

Consecutive patients carrying mtDNA mutations associated with MELAS and MSS were recruited and their serum concentrations of lactate, alanine, and heteroplasmic mtDNA mutant load were evaluated. The brain protocol included single‐voxel ¹H‐MRS (1.5T) in the medial parieto‐occipital cortex (MPOC), left cerebellar hemisphere, parieto‐occipital white matter (POWM), and lateral ventricles. Relative metabolite concentrations of N‐acetyl‐aspartate (NAA), choline (Cho), and myo‐inositol (mI) were estimated relative to creatine (Cr), using LCModel 6.3.

Results

Six patients with MELAS (age 28 ± 13 years, 3 [50%] female) and 17 with MSS (age 45 ± 11 years, 7 [41%] female) and 39 sex‐ and age‐matched healthy controls (HC) were enrolled. These patients demonstrated a lower NAA/Cr ratio in MPOC compared to HC (p = 0.006), which inversely correlated with serum lactate (p = 0.021, rho = −0.68) and muscle mtDNA heteroplasmy (p < 0.001, rho = −0.80). Similarly, in the cerebellum patients had lower NAA/Cr (p < 0.001), Cho/Cr (p = 0.002), and NAA/mI (p = 0.001) ratios, which negatively correlated with mtDNA blood heteroplasmy (p = 0.001, rho = −0.81) and with alanine (p = 0.050, rho = −0.67). Ventricular lactate was present in 78.3% (18/23) of patients, correlating with serum lactate (p = 0.024, rho = 0.58).

Conclusion

Correlations were found between the peripheral and biochemical markers of mitochondrial dysfunction and brain in vivo markers of neurodegeneration, supporting the use of both biomarkers as signatures of MELAS and MSS disease, to evaluate the efficacy of potential treatments.

Six-year prospective follow-up study in 151 carriers of the mitochondrial DNA 3243 A>G variant

BACKGROUND

The mitochondrial DNA (mDNA) 3243A>G variant is the most common pathogenic variant of the mDNA. To interpret results of clinical trials in mitochondrial disease, it is important to have a clear understanding of the natural course of disease. To obtain more insight into the disease burden and the progression of disease in carriers of the mDNA 3243 A>G variant, we followed a cohort of 151 carriers from 61 families prospectively for up to 6 years.

METHODS

The disease severity was scored using the Newcastle Mitochondrial Disease Adult Scale (NMDAS), including SF-36 quality of life (QoL) scores. Heteroplasmy levels were measured in urinary epithelial cells (UEC), leucocytes and saliva. The progression of the disease was studied using linear mixed model analysis.

RESULTS

One hundred twenty-four carriers (out of 151) were symptomatic. Four clinical groups were identified: 1) classical mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes syndrome (n=7), 2) maternally inherited diabetes deafness syndrome (n=60), 3) 'other' (n=57) and 4) dormant carriers (n=27). A yearly increase of NMDAS score of 0.47 point was measured in the total group. Heteroplasmy levels in both leucocytes and UEC were only weakly correlated with disease severity. Physical QoL declined with age. The most important determinants of QoL decline were hearing loss, speech problems, exercise intolerance, gait instability, psychiatric problems and gastrointestinal involvement.

CONCLUSION

The mDNA 3243 A>G variant causes a slowly progressive disease, with a yearly increase of NMDAS score of ~0.5 point overall with the clinical phenotype being the only determinant of disease progression.

Incidence and predictors of total mortality in 267 adults presenting with mitochondrial diseases

Assessing long-term mortality and identifying predictors of death in adults with mitochondrial diseases. We retrospectively included adult patients with genetically proven mitochondrial diseases referred to our centre between January 2000 and June 2016, and collected information relative to their genetic testing, clinical assessments, and vital status. We performed single and multiple variable analyses in search of predictors of total mortality, and calculated hazard ratios (HR) and 95% confidence intervals (CI). We included 267 patients (women 59%; median age 43.3 [31.3-54.2] years), including 111 with mitochondrial DNA (mtDNA) single large-scale deletions, 65 with m.3243A>G, 24 with m.8344A>G, 32 with other mtDNA point mutations, and 36 patients with nuclear genes mutations. Over a median follow-up of 8.9 years (0.3 to 18.7), 61 patients (22.8%) died, at a median age of 50.7 (37.9-51.9) years. Primary cause of death was cardiovascular disease in 16 patients (26.2%), respiratory in 11 (18.0%), and gastrointestinal in 5 (8.1%). By multiple variable analysis, diabetes (HR 2.75; 95% CI 1.46-5.18), intraventricular cardiac conduction defects (HR 3.38; 95% CI 1.71-6.76) and focal brain involvement (HR 2.39; 95% CI 1.25-4.57) were independent predictors of death. Adult patients with mitochondrial diseases present high morbidity that can be independently predicted by the presence of diabetes, intraventricular cardiac conduction defects, and focal brain involvement.

Systematic review of cognitive deficits in adult mitochondrial disease

The profile and trajectory of cognitive impairment in mitochondrial disease are poorly defined. This systematic review sought to evaluate the current literature on cognition in mitochondrial disease, and to determine future research directions. A systematic review was conducted, employing PubMed, Medline, Psycinfo, Embase and Web of Science, and 360‐degree citation methods. English language papers on adult patients were included. The literature search yielded 2421 articles, of which 167 met inclusion criteria. Case reports and reviews of medical reports of patients yielded broad diagnoses of dementia, cognitive impairment and cognitive decline. In contrast, systematic investigations of cognitive functioning using detailed cognitive batteries identified focal cognitive rather than global deficits. Results were variable, but included visuospatial functioning, memory, attention, processing speed and executive functions. Conclusions from studies have been hampered by small sample sizes, variation in genotype and the breadth and depth of assessments undertaken. Comprehensive cognitive research with concurrent functional neuroimaging and physical correlates of mitochondrial disease in larger samples of well‐characterized patients may discern the aetiology and progression of cognitive deficits. These data provide insights into the pattern and trajectory of cognitive impairments, which are invaluable for clinical monitoring, health planning and clinical trial readiness.

Resolving complexity in mitochondrial disease: Towards precision medicine

Mitochondrial diseases, caused by mutations in either the nuclear or mitochondrial genomes (mtDNA), are the most common form of inherited neurometabolic disorders. They are remarkably heterogeneous, both in their clinical presentation and genetic etiology, presenting challenges for diagnosis, clinical management and elucidation of molecular mechanism. The multifaceted nature of these diseases, compounded by the unique characteristics of mitochondrial genetics, cement their space in the field of complex disease. In this review we examine the m.3243A>G variant, one of the most prevalent mitochondrial DNA mutations, using it as an exemplar to demonstrate the challenges presented by these complex disorders. Disease caused by m.3243A>G is one of the most phenotypically diverse of all mitochondrial diseases; we outline known causes of this heterogeneity including mtDNA heteroplasmy, mtDNA copy number and nuclear genetic factors. We consider the impact that this has in the clinic, discussing the personalized management of common manifestations attributed to this pathogenic mtDNA variant, including hearing impairment, diabetes mellitus, myopathy, cardiac disease, stroke-like episodes and gastrointestinal disturbances. Future research into this complex disorder must account for this heterogeneity, benefitting from the use of large patient cohorts to build upon current clinical expertise. Through multi-disciplinary collaboration, the complexities of this mitochondrial disease can be addressed with the variety of diagnostic, prognostic, and treatment approaches that are moulded to best fit the needs of each individual patient.

Levetiracetam administration is correlated with lower mortality in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes: a retrospective study

Background:

Studies on the relationship between antiepileptic drug (AED) administration and clinical outcomes in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) remain scarce. Levetiracetam (LEV) is an AED that is neuroprotective in various neurologic disorders. This study aimed to determine the impact of LEV on the outcome of MELAS.

Methods:

A retrospective, single-center study was performed based on a large cohort of patients with MELAS with a history of seizures (n = 102). Decisions on antiepileptic therapies were made empirically. Patients were followed up for 1 to 8 years (median, 4 years) and divided into 2 groups based on whether LEV was administered (LEV or non-LEV). The modified Rankin scale (mRS) scores and mortality risks were analyzed in all patients.

Results:

LEV, carbamazepine, benzodiazepines, topiramate, oxcarbazepine, valproate, and lamotrigine were administered in 48, 37, 18, 13, 11, 9, and 9 patients, singly or in combination, respectively. The mean mRS score of the LEV group (n = 48) was lower than that of the non-LEV group (n = 54; mean ± standard deviation, 2.79 ± 1.47 vs. 3.83 ± 1.93, P = 0.006) up to the end of the study. Nevertheless, there was no difference in the proportion of subjects without disability (mRS ranging 0–1) between the groups (P = 0.37). The multivariate regressions revealed that LEV treatment was associated with lower mRS scores (odds ratio 0.32, 95% confidence interval [CI] 0.15–0.68, P = 0.003) and mortality rates (hazard ratio 0.24, 95% CI 0.08–0.74, P = 0.013). There was a significant difference in the Kaplan-Meier survival curves between the groups (χ² = 4.29, P = 0.04).

Conclusions:

The LEV administration is associated with lower mortality in patients with MELAS in this retrospective study. Further laboratory research and prospective cohort studies are needed to confirm whether LEV has neuroprotective effects on patients with mitochondrial diseases.

Taurine supplementation for prevention of stroke-like episodes in MELAS: a multicentre, open-label, 52-week phase III trial

OBJECTIVE

The aim of this study was to evaluate the efficacy and safety of high-dose taurine supplementation for prevention of stroke-like episodes of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes), a rare genetic disorder caused by point mutations in the mitochondrial DNA that lead to a taurine modification defect at the first anticodon nucleotide of mitochondrial tRNA^Leu(UUR), resulting in failure to decode codons accurately.

METHODS

After the nationwide survey of MELAS, we conducted a multicentre, open-label, phase III trial in which 10 patients with recurrent stroke-like episodes received high-dose taurine (9 g or 12 g per day) for 52 weeks. The primary endpoint was the complete prevention of stroke-like episodes during the evaluation period. The taurine modification rate of mitochondrial tRNA^Leu(UUR) was measured before and after the trial.

RESULTS

The proportion of patients who reached the primary endpoint (100% responder rate) was 60% (95% CI 26.2% to 87.8%). The 50% responder rate, that is, the number of patients achieving a 50% or greater reduction in frequency of stroke-like episodes, was 80% (95% CI 44.4% to 97.5%). Taurine reduced the annual relapse rate of stroke-like episodes from 2.22 to 0.72 (P=0.001). Five patients showed a significant increase in the taurine modification of mitochondrial tRNA^Leu(UUR) from peripheral blood leukocytes (P<0.05). No severe adverse events were associated with taurine.

CONCLUSIONS

The current study demonstrates that oral taurine supplementation can effectively reduce the recurrence of stroke-like episodes and increase taurine modification in mitochondrial tRNA^Leu(UUR) in MELAS.

TRIAL REGISTRATION NUMBER

UMIN000011908.

Cognitive deficits in adult m.3243A>G- and m.8344A>G-related mitochondrial disease: importance of correcting for baseline intellectual ability

Objective

To determine the cognitive profile of adult patients with mitochondrial disease, and the effect of disease severity on cognition.

Methods

Using a prospective case-control design, we compared cognition of patients to normative data and to matched controls, assessed three times over 18 months. Forty-nine patients with m.3243A>G (N = 36) and m.8344A>G (N = 13) mtDNA mutations and 32 controls, matched by age (±5 years) and premorbid cognition (±10 WTAR FSIQ points), participated. Participants completed neuropsychological assessments of general cognition (WAIS-IV), executive function (D-KEFS), and memory (WMS-IV). Potential predictors of cognition were explored.

Results

Patients show mild-to-moderate premorbid cognitive impairment, but substantial impairment in current general cognition and distinct domains, including verbal comprehension, perceptual reasoning, working memory, processing speed, and memory retrieval. Executive dysfunction may be caused by slower decision-making. Patients performed worse than controls, except on memory tasks, indicating intact memory, when premorbid cognition is controlled for. Premorbid cognition and disease severity were consistent predictors of cognition in patients; however, cognitive decline appears slow and is unlikely in the short-term, when other disease-specific factors remain stable.

Interpretation

Patients should be monitored to facilitate early identification of a complex profile of cognitive deficits and individuals with higher disease burden should be followed up more closely. On development of cognitive difficulties, appropriate compensatory strategies should be determined through in-depth assessment. Using strategies such as slower presentation of information, multiple modes of presentation, active discussion to aid understanding and decision-making, and use of memory aids, may ameliorate difficulties.

CPEO - Like mitochondrial myopathy associated with m.8340G>A mutation

Two patients with an m.8340G>A mitochondrial DNA variant have been reported with one patient showing ptosis, ophthalmoparesis and myopathy at 53% heteroplasmy and another with pigmentary retinopathy, cataracts and sensory neural deafness and slightly higher heteroplasmy (65%). Here we report that higher muscle mutant heteroplasmy (93%) for m.8340G>A is associated with ptosis, ophthalmoparesis and mitochondrial myopathy, thus confirming the initial phenotypic association and showing that heteroplasmy per se does not explain the phenotypic spectrum of disease associated with the m.8340G>A mutation.

MERRF Classification: Implications for Diagnosis and Clinical Trials

BACKGROUND

Given the etiologic heterogeneity of disease classification using clinical phenomenology, we employed contemporary criteria to classify variants associated with myoclonic epilepsy with ragged-red fibers (MERRF) syndrome and to assess the strength of evidence of gene-disease associations. Standardized approaches are used to clarify the definition of MERRF, which is essential for patient diagnosis, patient classification, and clinical trial design.

METHODS

Systematic literature and database search with application of standardized assessment of gene-disease relationships using modified Smith criteria and of variants reported to be associated with MERRF using modified Yarham criteria.

RESULTS

Review of available evidence supports a gene-disease association for two MT-tRNAs and for POLG. Using modified Smith criteria, definitive evidence of a MERRF gene-disease association is identified for MT-TK. Strong gene-disease evidence is present for MT-TL1 and POLG. Functional assays that directly associate variants with oxidative phosphorylation impairment were critical to mtDNA variant classification. In silico analysis was of limited utility to the assessment of individual MT-tRNA variants. With the use of contemporary classification criteria, several mtDNA variants previously reported as pathogenic or possibly pathogenic are reclassified as neutral variants.

CONCLUSIONS

MERRF is primarily an MT-TK disease, with pathogenic variants in this gene accounting for ~90% of MERRF patients. Although MERRF is phenotypically and genotypically heterogeneous, myoclonic epilepsy is the clinical feature that distinguishes MERRF from other categories of mitochondrial disorders. Given its low frequency in mitochondrial disorders, myoclonic epilepsy is not explained simply by an impairment of cellular energetics. Although MERRF phenocopies can occur in other genes, additional data are needed to establish a MERRF disease-gene association. This approach to MERRF emphasizes standardized classification rather than clinical phenomenology, thus improving patient diagnosis and clinical trial design.

Left ventricular hypertrophy and cognitive function: a systematic review

Cognitive impairment is common in patients with hypertension. Left ventricular hypertrophy (LVH) is recognised as a marker of hypertension-related organ damage and is a strong predictor of coronary artery disease, heart failure and stroke. There is evidence that LVH is independently associated with cognitive impairment, even after adjustment for the presence of hypertension. We conducted a systematic review that examined cognitive impairment in adults with LVH. Independent searches were performed in Ovid MEDLINE, Ovid psycInfo and PubMed with the terms left ventricular hypertrophy and cognition. Seventy-three studies were identified when both searches were combined. After limiting the search to studies that were: (1) reported in English; (2) conducted in humans; (3) in adults aged 50 years and older; and (4) investigated the relationship between LVH and cognitive performance, nine papers were included in this systematic review. The majority of studies found an association between LVH and cognitive performance. Inspection of results indicated that individuals with LVH exhibited a lower performance in cognitive tests, when compared to individuals without LVH. Memory and executive functions were the cognitive domains that showed a specific vulnerability to the presence of LVH. A possible mechanism for the relationship between LVH and cognition is the presence of cerebral white matter damage. White matter lesions occur frequently in patients with LVH and may contribute to cognitive dysfunction. Together, the results of this review suggest that memory impairment and executive dysfunction are the cognitive domains that showed a particular association with the presence of LVH.

Prediction of long-term prognosis by heteroplasmy levels of the m.3243A>G mutation in patients with the mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes syndrome

BACKGROUND AND PURPOSE

Our aim was to determine the prognostic value of urine and blood heteroplasmy in patients with the m.3243A>G mutation.

METHODS

Adults with the m.3243A>G mutation referred to our institution between January 2000 and May 2014 were retrospectively included. The relationship between their baseline clinical characteristics, their mutation load in urine and blood, and major adverse events (MAEs) during follow-up, defined as medical complications requiring a hospitalization or complicated by death, was studied.

RESULTS

Of the 43 patients (age 45.6 ± 13.3 years) included in the study, 36 patients were symptomatic, including nine with evidence of focal brain involvement, and seven were asymptomatic. Over a 5.5 ± 4.0 year mean follow-up duration, 14 patients (33%) developed MAEs. Patients with MAEs had a higher mutation load than others in urine (60.1% ± 13.8% vs. 40.6% ± 26.2%, P = 0.01) and in blood (26.9% ± 18.4% vs. 16.0% ± 12.1%, P = 0.03). Optimal cutoff values for the prediction of MAEs were 45% for urine and 35% for blood. In multivariate analysis, mutation load in urine ≥45% [odds ratio 25.3; 95% confidence interval (CI) 1.1-567.8; P = 0.04], left ventricular hypertrophy (odds ratio 16.7; 95% CI 1.3- 222.5; P = 0.03) and seizures (odds ratio 48.3; 95% CI 2.5-933; P = 0.01) were associated with MAEs.

CONCLUSIONS

Patients with the m.3243A>G mutation are at high risk of MAEs, which can be independently predicted by mutation load in urine ≥45%, a personal history of seizures, and left ventricular hypertrophy.

Three families with 'de novo' m.3243A > G mutation

The m.3243A > G mutation is the most prevalent, disease-causing mitochondrial DNA (mtDNA) mutation. In a national cohort study of 48 families harbouring the m.3243A > G mutation, we identified three families in which the mutation appeared to occur sporadically within these families. In this report we describe these three families. Based on detailed mtDNA analysis of three different tissues using two different quantitative pyrosequencing assays with sensitivity to a level of 1% mutated mtDNA, we conclude that the m.3243A > G mutation has arisen de novo in each of these families. The symptomatic carriers presented with a variety of symptoms frequently observed in patients harbouring the m.3243A > G mutation. A more severe phenotype is seen in the de novo families compared to recent cohort studies, which might be due to reporting bias.

The observation that de novo m.3243A > G mutations exist is of relevance for both diagnostic investigations and genetic counselling. Firstly, even where there is no significant (maternal) family history in patients with stroke-like episodes, diabetes and deafness or other unexplained organ dysfunction, the m.3243A > G mutation should be screened as a possible cause of the disease. Second, analysis of maternally-related family members is highly recommended to provide reliable counselling for these families, given that the m.3243A > G mutation may have arisen de novo.

•

De novo m.3243A > G mutations are more frequent than previously reported.

•

Even in absence of a family history, the. m.3243A > G mutation should be considered.

•

Testing maternally-related family members is needed to provide reliable counselling.

Audio profiles in mitochondrial deafness m.1555A>G and m.3243A>G show distinct differences

BACKGROUND

Hearing loss is one of the most common symptoms of mitochondrial disorders. However, audiological phenotypes associated with different molecular defects in mtDNA are not yet well characterized.

MATERIAL AND METHODS

A large cohort of 1499 nonconsanguineous patients aged 5-40 years with hearing loss of unknown etiology was screened for mutations in mtDNA. For further analysis, patients harboring m.1555A>G and m.3243A>G were selected. Hearing status of the patients was assessed by pure tone audiometry. Patterns of audiograms (hearing threshold levels at each examined frequency) were statistically compared among the carriers of the m.1555A>G and the m.3243A>G mutations.

RESULTS

We identified 20 patients positive for m.1555A>G mutation and 16 patients positive for m.3243A>G change. The frequency of the above transitions was calculated in our cohort as 1.33% and 1.06%, respectively. Seventeen affected family members carrying the mutations were included into the study. Typical shape of the audiograms in patients with m.1555A>G mutation presented a ski-slope pattern, whereas the audiometric curves among the m.3243A>G individuals had a pantonal shape (a flat curve) with slight downward sloping at the higher frequencies. The differences were statistically significant. The onset of hearing loss was noted earlier among m.1555A>G than m.3243A>G patients (12.5 and 26 years, respectively). Aminoglycoside administration was declared in both groups in 11 and 4 cases respectively, and caused abrupt hearing deterioration in all cases.

CONCLUSIONS

A pattern of audiogram in patients with mitochondrial deafness may suggest a localization of mtDNA mutation. The pathogenesis of the audiometric differences needs further study.

The broadening spectrum of mitochondrial disease: shifts in the diagnostic paradigm

BACKGROUND

The diagnosis of mitochondrial disease requires a complex synthesis of clinical, biochemical, histological, and genetic investigations. An expanding number of mitochondrial diseases are being recognized, despite their phenotypic diversity, largely due to improvements in methods to detect mutations in affected individuals and the discovery of genes contributing to mitochondrial function. Improved understanding of the investigational pitfalls and the development of new laboratory methodologies that lead to a molecular diagnosis have necessitated the field to rapidly adopt changes to its diagnostic approach.

SCOPE OF REVIEW

We review the clinical, investigational and genetic challenges that have resulted in shifts to the way we define and diagnose mitochondrial disease. Incorporation of changes, including the use of fibroblast growth factor 21 (FGF-21) and next generation sequencing techniques, may allow affected patients access to earlier molecular diagnosis and management.

MAJOR CONCLUSIONS

There have been important shifts in the diagnostic paradigm for mitochondrial disease. Diagnosis of mitochondrial disease is no longer reliant on muscle biopsy alone, but should include clinical assessment accompanied by the use of serological biomarkers and genetic analysis. Because affected patients will be defined on a molecular basis, oligosymptomatic mutation carriers should be included in the spectrum of mitochondrial disease. Use of new techniques such as the measurement of serum FGF-21 levels and next-generation-sequencing protocols should simplify the diagnosis of mitochondrial disease.

GENERAL SIGNIFICANCE

Improvements in the diagnostic pathway for mitochondrial disease will result in earlier, cheaper and more accurate methods to identify patients with mitochondrial disease. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.

Cardiac involvement in mitochondrial DNA disease: clinical spectrum, diagnosis, and management

Mitochondrial disease refers to a heterogenous group of genetic disorders that result from dysfunction of the final common pathway of energy metabolism. Mitochondrial DNA mutations affect key components of the respiratory chain and account for the majority of mitochondrial disease in adults. Owing to critical dependence of the heart on oxidative metabolism, cardiac involvement in mitochondrial disease is common and may occur as the principal clinical manifestation or part of multisystem disease. Recent advances in our understanding of the clinical spectrum and genetic aetiology of cardiac involvement in mitochondrial DNA disease have important implications for cardiologists in terms of the investigation and multi-disciplinary management of patients.

Postlingual hearing loss as a mitochondrial 3243A>G mutation phenotype

Background

The prevalence of isolated hearing loss (HL) associated with the m.3243A>G mutation is unknown. The aim of this study was to assess the frequency and heteroplasmy level of the m.3243A>G mutation in a large group of Polish patients with postlingual bilateral sensorineural HL of unidentified cause.

Methodology/Principal Findings

A molecular search was undertaken in the archival blood DNA of 1482 unrelated patients with isolated HL that had begun at ages between 5 and 40 years. Maternal relatives of the probands were subsequently investigated and all carriers underwent audiological tests. The m.3243A>G mutation was found in 16 of 1482 probands (an incidence of 1.08%) and 18 family members. Of these 34 individuals, hearing impairment was detected in 29 patients and the mean onset of HL was at 26 years. Some 42% of the identified m.3243A>G carriers did not develop multisystem symptomatology over the following 10 years. Mean heteroplasmy level of m.3243A>G was lowest in blood at a level of 14% and highest in urine at 58%. These values were independent of the manifested clinical severity of the disease.

Conclusions

A single m.3243A>G carrier can usually be found among each 100 individuals who have postlingual hearing loss of unknown cause. Urine samples are best for detecting the m.3243A>G mutation and diagnosing mitochondrially inherited hearing loss.

Cardiac manifestations of neurologic disorders

The cardiac complications of certain neurologic diseases have been well recognized for over 50 years and are mostly evident for cerebrovascular accidents. Although these complications are frequent and in most circumstances benign, detrimental cardiac side effects, such as serious arrhythmias and myocardial infarctions, may occur. The link to most of these cardiac derangements is a transient or chronic autonomic dysfunction, depending on the specific neurologic disease. Myocardial infarcts, left ventricular dysfunction, and arrhythmias are well-recognized complications of subarachnoid hemorrhage, intracranial bleed, and ischemic strokes. Seizures may present with atonia or sudden death from asystole. Degenerative brain disorders, namely the synucleinopathies, may affect the central control areas or peripheral ganglia of the autonomic nervous system, causing autonomic dysfunction. In addition, cardiac conduction defects and cardiomyopathy are common in certain neuromuscular disorders, namely the dystrophies and mitochondrial myopathies.

Inheritance of the m.3243A>G mutation

The m.3243A>G is the most prevalent pathogenic mtDNA mutation but little is known about its inheritance. We studied 34 families containing 56 mother-child relations and 82 intersibling relations to investigate its transmission. We found a significant correlation between mother and child heteroplasmy levels (r = 0.679, p < 0.001). In mothers with a heteroplasmy level of below 25% we found 30% offspring without detectable mutation, while in mothers with a heteroplasmy level of above 25%, 100% of the offspring showed the m.3243A>G mutation. Heteroplasmy levels between siblings also correlated (r = 0.512, p < ;0.001), but had limited extra predictive value because of outliers. These new data on inheritance of the m.3243A>G mutation might be of value in counseling patients and preventing transmission of the mutation.

Prognosis of symptomatic patients with the A3243G mutation of mitochondrial DNA

BACKGROUND/PURPOSE

The clinical analyses and prognoses of mitochondrial diseases with A3243G mutation are rarely documented in Taiwan. Our study investigated the clinical phenotypes and the outcomes of patients with mitochondrial disease and the A3243G mutation of mtDNA in a Taiwanese population, and compared these with previous reports.

METHODS

We retrospectively studied 22 consecutive patients with mitochondrial disease and the A3243G mutation of mtDNA in Chang Gung Memorial Hospital between 1988 and 2009. All patients underwent a detailed demographic registration, neurological examinations, a muscle biopsy, and mitochondrial DNA analysis. Modified Rankin scale, the presence of recurrent strokes or seizures, critical medical complications, and death were monitored during the follow-up period.

RESULTS

Of the 22 patients, seizures and stroke-like episodes were found in 12 (55%). Visceral involvement, including cardiomyopathy, nephropathy, and pulmonary hypertension, were noted in five patients (23%). Patients with seizures had a high frequency of status epilepticus (92%) and a younger age of onset (21.3±7.2 years). Both the Kaplan-Meier survival analysis and the Cox-regression model showed a marked deterioration in patients with seizures after 7 years of follow-up.

CONCLUSION

Our study found that seizures and status epilepticus are the most important predictive values for a poor outcome in patients with the mtA3243G mutation of mtDNA. Age of onset and visceral organ involvement had no prominent influence on the prognosis. Some medical complications could be well controlled or even reversed after management.

Natural history of MELAS associated with mitochondrial DNA m.3243A>G genotype

OBJECTIVE

To describe the natural history of clinical and laboratory features associated with the m.3243A>G mitochondrial DNA point mutation. Natural history data are needed to obtain prognostic information and for clinical trial planning.

METHODS

We included 85 matrilineal relatives from 35 families with at least 2 visits in this prospective cohort study. Thirty-one were fully symptomatic with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), and 54 were carrier relatives. Evaluations included standardized questionnaires (medical history and daily living functioning), physical examination, neuropsychological testing, and a battery of imaging and laboratory tests. We evaluated changes in clinical and laboratory features over time and survival. Outcomes are reported over a follow-up period of up to 10.6 years (mean 3.8 ± 2.2 years for patients and 5.5 ± 3.0 for carrier relatives).

RESULTS

Neurologic examination, neuropsychological testing, and daily living scores significantly declined in all patients with MELAS, whereas no significant deterioration occurred in carrier relatives. Cerebral MRI scores declined significantly in patients with MELAS. Magnetic resonance spectroscopy estimates of lactate in the lateral ventricles increased over time, and high lactate was associated with increased mortality. Symptom onset in childhood often was associated with worse outcome. Patients with MELAS had a greater death rate than carrier relatives.

CONCLUSIONS

Patients with MELAS carrying the m.3243A>G mutation show a measurable decline in clinical and imaging outcomes. It is hoped that these data will be helpful in anticipating the disease course and in planning clinical trials for MELAS.

Mitochondrial-nuclear epistasis: implications for human aging and longevity

There is substantial evidence that mitochondria are involved in the aging process. Mitochondrial function requires the coordinated expression of hundreds of nuclear genes and a few dozen mitochondrial genes, many of which have been associated with either extended or shortened life span. Impaired mitochondrial function resulting from mtDNA and nuclear DNA variation is likely to contribute to an imbalance in cellular energy homeostasis, increased vulnerability to oxidative stress, and an increased rate of cellular senescence and aging. The complex genetic architecture of mitochondria suggests that there may be an equally complex set of gene interactions (epistases) involving genetic variation in the nuclear and mitochondrial genomes. Results from Drosophila suggest that the effects of mtDNA haplotypes on longevity vary among different nuclear allelic backgrounds, which could account for the inconsistent associations that have been observed between mitochondrial DNA (mtDNA) haplogroups and survival in humans. A diversity of pathways may influence the way mitochondria and nuclear-mitochondrial interactions modulate longevity, including: oxidative phosphorylation; mitochondrial uncoupling; antioxidant defenses; mitochondrial fission and fusion; and sirtuin regulation of mitochondrial genes. We hypothesize that aging and longevity, as complex traits having a significant genetic component, are likely to be controlled by nuclear gene variants interacting with both inherited and somatic mtDNA variability.

Voxelwise analysis of diffusion tensor imaging and structural MR imaging in patients with the m.3243A>G mutation in mitochondrial DNA

BACKGROUND AND PURPOSE

The m.3243A>G mutation is the most common pathogenic mutation in mtDNA; tissues with high dependence on aerobic energy metabolism, such as the brain, heart, and skeletal muscle, are most affected by the ensuing mitochondrial dysfunction. We hypothesized that the m.3243A>G mutation manifests as disturbances in white matter microstructural integrity and volumetric changes in the brain.

MATERIALS AND METHODS

DTI and structural MR imaging were performed on 15 adult patients with the m.3243A>G mutation and 14 healthy age-matched controls. Voxelwise analysis of the DTI data was performed to reveal possible differences in FA and MD values. Additionally, normalized brain tissue volumes of the subjects were measured, and voxelwise analysis of gray matter was performed to assess volumetric changes in the brain.

RESULTS

Among patients with m.3243A>G mutation, voxelwise analysis of the DTI data revealed significantly reduced FA in several areas located mainly in the occipital lobes, thalami, external and internal capsules, brain stem, cerebellar peduncles, and cerebellar white matter. There were no differences in MD values between the patients and the controls. Analysis of the structural MR imaging data revealed reduced total volume of gray and white matter in patients with m.3243A>G mutation, and VBM analysis identified areas of significant gray matter loss mainly in the occipital lobes and cerebellum.

CONCLUSIONS

Our findings show that patients with m.3243A>G mutation have mild microstructural damage leading to loss of directional organization of white matter and reduced brain volumes.

Craniofacial morphology in children of mothers with the m.3243A>G mutation in mitochondrial DNA

OBJECTIVE

To describe craniofacial morphology in children from families with the mitochondrial encephalomyopathy, lactic acidosis, stroke-like episodes (MELAS) syndrome.

DESIGN

Transversal prospective case-control study from a tertiary center.

SUBJECTS

Nine children (five girls, four boys; aged 7.5 to 15.3 years) of mothers with m.3243A>G mutation in mitochondrial DNA and 36 age- and sex-matched healthy children as controls.

METHODS

Seventy-three cephalometric variables representing craniofacial and dental features were analyzed in lateral radiographs. The statistical dependence caused by intrafamilial correlation was taken into account by using a two-level analysis of variance model that was fitted to the data using SAS procedure MIXED.

RESULTS

The frontal bone was thicker and the frontal sinus, mandibular symphysis width, and lower posterior face height were larger in the subjects than in the controls. Upper incisors were more labially inclined, and the interincisal angle was smaller in subjects than in the control children.

CONCLUSIONS

Differences were found in craniofacial structures between the children of mothers with m.3243A>G and unaffected children. Differences in the upper incisor inclination, mandibular symphysis width, and lower posterior face height suggest an altered mandibular growth pattern in the subjects. In addition, the children had cranial aberrations such as larger frontal sinuses and the thicker frontal bone.

Autonomic symptoms in carriers of the m.3243A>G mitochondrial DNA mutation

BACKGROUND

The m.3243A>G mutation can cause multisystem medical problems and can affect the autonomic nervous system.

OBJECTIVE

To study the frequency and spectrum of autonomic symptoms associated with the m.3243A>G mitochondrial DNA point mutation. Design, Setting, and Patients We studied a cohort of 88 matrilineal relatives from 40 families, including 35 fully symptomatic patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS), 53 carrier relatives, and 16 controls using a questionnaire based on existing standard instruments for the evaluation of autonomic dysfunction. We compared the questionnaire with an expert evaluation. We compared data among the 3 groups using the Mantel-Haenszel chi(2) test to determine the statistical significance of differences between groups.

RESULTS

Mutation carriers frequently had symptoms of autonomic dysfunction, specifically gastrointestinal and orthostatic intolerance.

CONCLUSIONS

Carriers of the m.3243A>G mutation have frequent autonomic symptoms. The m.3243A>G mutation should be considered as an etiological factor in patients with autonomic dysfunction and a medical or family history suggestive of mitochondrial disease. Because some autonomic symptoms are treatable, early detection and proactive management may mitigate the burden of morbidity.

Cerebral oxygen and glucose metabolism in patients with mitochondrial m.3243A>G mutation

The m.3243A>G mutation is the most common pathogenic mutation in mitochondrial DNA. It leads to defective oxidative phosphorylation, decreased oxygen consumption and increased glucose utilization and lactate production in vitro. However, oxygen and glucose metabolism has not been studied in the brain of patients harbouring the m.3243A>G mutation. Therefore, 14 patients with the m.3243A>G mutation, not experiencing acute stroke-like episodes and 14 age-matched controls underwent positron emission tomography using 2-[(18)F]fluoro-2-deoxyglucose, [(15)O]H(2)O and [(15)O]O(2) as the tracers during normoglycaemia. The metabolic rate of oxygen and glucose were determined using a quantitative region of interest analysis. Metabolites in unaffected periventricular tissue were measured using magnetic resonance spectroscopy. We found that the cerebral metabolic rate of oxygen was decreased by 26% (range 18%-29%) in the grey as well as the white matter of patients with the m.3243A>G mutation. A decrease in the metabolic rate of glucose was found with predilection to the posterior part of the brain. No major changes were detected in cerebral blood flow or the number of white matter lesions. Our results show that the m.3243A>G mutation leads to a global decrease in oxygen consumption in the grey matter including areas where no other signs of disease were present.

Role of mitochondrial variation in maternally inherited diabetes and deafness syndrome

Maternally inherited diabetes and deafness syndrome is caused by the mitochondrial deoxyribonucleic acid mutation 3243 A>G (where A = adenine and G = guanine). The degree of heteroplasmy of the mitochondrial deoxyribonucleic acid may correlate with the rate of progression of the hearing loss. This has important implications for counselling patients with this pathology. Cochlear implantation is a successful method of rehabilitation for patients with hearing loss as part of this syndrome.

Mouse models of oxidative phosphorylation defects: powerful tools to study the pathobiology of mitochondrial diseases

Defects in the oxidative phosphorylation system (OXPHOS) are responsible for a group of extremely heterogeneous and pleiotropic pathologies commonly known as mitochondrial diseases. Although many mutations have been found to be responsible for OXPHOS defects, their pathogenetic mechanisms are still poorly understood. An important contribution to investigate the in vivo function of several mitochondrial proteins and their role in mitochondrial dysfunction, has been provided by mouse models. Thanks to their genetic and physiologic similarity to humans, mouse models represent a powerful tool to investigate the impact of pathological mutations on metabolic pathways. In this review we discuss the main mouse models of mitochondrial disease developed, focusing on the ones that directly affect the OXPHOS system.

Migraine and stroke: current perspectives

OBJECTIVE

The purpose of this article is to review the latest concepts regarding migraine and ischemic stroke. In addition, focal neurological deficits and MRI changes in migraine patients will be reviewed.

METHODS

A PubMed search of neurological literature pertaining to this study was conducted using specific keyword search terms pertaining to migraine and ischemic stroke.

RESULTS

Migraine, especially with aura, is a relative risk factor for stroke. Neuroimaging demonstrates the posterior circulation as being most vulnerable, although the reason for this distribution is unclear. Factors that may contribute to stroke in migraine include changes during cortical spreading depression with hyper- or hypoperfusion of neural tissue, vasospasm and endothelial dysfunction. Estrogen affects migraine expression as well as cerebral circulation, yet most women with migraine without aura are not at increased risk. Co-morbidity with patent foramen ovale can be mechanism of both disorders via presumed lack of filtration of microemboli or toxic substances; however, closure with reversal of right to left shunt seems to be more beneficial for cryptogenic stroke than migraine. Migraine and stroke are found in specific genetic disorders such as CADASIL, HERNS and MELAS giving clues to genetic factors. Stroke associated with migraine treatments such as ergots or triptans is rare, and usually associated with special circumstances such as overuse or concomitant thrombogenic conditions.

CONCLUSION

Although true migrainous infarction is rare, our understanding of the subtle associations between migraine and cerebrovascular behavior is expanding.

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.

Accurate consent for insertion and later removal of grommets

Each year in the UK over 30 000 patients undergo insertion of grommets. The grommet insertion may cause many problems like persistent otorrhoea, scarred drum, retraction pockets and retention. The grommets may be extruded from the middle ears by the normal epithelial migration mechanism once they have served their purpose. These may become infected and require removal. We have analysed the Department of Health Hospital Episode Statistics relating to the insertion and removal of grommets (ventilation tubes). We have shown that 7.6 per cent of patients who have grommets inserted will have grommets removed.

Free Radicals, Mitochondria, and Oxidized Lipids

Mitochondria have long been known to play a critical role in maintaining the bioenergetic status of cells under physiological conditions. It was also recognized early in mitochondrial research that the reduction of oxygen to generate the free radical superoxide occurs at various sites in the respiratory chain and was postulated that this could lead to mitochondrial dysfunction in a variety of disease states. Over recent years, this view has broadened substantially with the discovery that reactive oxygen, nitrogen, and lipid species can also modulate physiological cell function through a process known as redox cell signaling. These redox active second messengers are formed through regulated enzymatic pathways, including those in the mitochondrion, and result in the posttranslational modification of mitochondrial proteins and DNA. In some cases, the signaling pathways lead to cytotoxicity. Under physiological conditions, the same mediators at low concentrations activate the cytoprotective signaling pathways that increase cellular antioxidants. Thus, it is critical to understand the mechanisms by which these pathways are distinguished to develop strategies that will lead to the prevention of cardiovascular disease. In this review, we describe recent evidence that supports the hypothesis that mitochondria have an important role in cell signaling, and so contribute to both the adaptation to oxidative stress and the development of vascular diseases.