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.

Design and baseline characteristics of the Biomarkers Of Risk In Colorectal Cancer (BORICC) Follow-Up study: A 12+ years follow-up.

BACKGROUND: Colorectal cancer (CRC) is the third most common cancer worldwide. Age is the strongest non-modifiable risk factor but it is estimated that over half of CRC cases are linked with lifestyle factors such as diet. The Biomarkers Of RIsk of Colorectal Cancer (BORICC) Study recruited 363 participants in 2005 to investigate the effects of lifestyle factors on biomarkers of CRC risk. AIM: In the present BORICC Follow-Up (BFU) Study, we are using a longitudinal study design to investigate the effects of ageing (12+ years) and lifestyle factors on biomarkers of CRC risk and on healthy ageing. METHODS: BFU Study participants attended a study visit at North Tyneside General Hospital (UK) for collection of biological samples, including blood and rectal biopsies, and information collected included anthropometric measurements, a Health & Medications Questionnaire, physical activity and sedentary behaviour, and habitual diet. Furthermore, musculoskeletal function was assessed by heel bone densitometry, timed up and go and hand grip strength as markers of healthy ageing. The BFU Study outcomes will be similar to those measured at baseline in the BORICC Study, such as DNA methylation and mitochondrial function, with additional measurements including the gut microbiome, faecal short-chain fatty acid concentrations and expression of genes associated with CRC. RESULTS: Participants' recruitment to BFU Study and all sample and data collection have been completed. Forty-seven of the original BORICC participants were re-recruited to the BFU Study (mean age 67 years, 51% female). The recruits included 37 initially healthy participants and 10 participants who had adenomatous polyps at baseline. Approximately 70% of participants were over-weight or obese. CONCLUSION: Ultimately, identifying lifestyle factors that can reduce CRC risk, and understanding the underlying mechanisms for the effects of lifestyle and ageing on CRC risk, could lead to early prevention strategies.

Effects of obesity and weight loss on mitochondrial structure and function and implications for colorectal cancer risk.

Colorectal cancer (CRC) is the third most common cancer globally. CRC risk is increased by obesity, and by its lifestyle determinants notably physical inactivity and poor nutrition. Obesity results in increased inflammation and oxidative stress which cause genomic damage and contribute to mitochondrial dysregulation and CRC risk. The mitochondrial dysfunction associated with obesity includes abnormal mitochondrial size, morphology and reduced autophagy, mitochondrial biogenesis and expression of key mitochondrial regulators. Although there is strong evidence that increased adiposity increases CRC risk, evidence for the effects of intentional weight loss on CRC risk is much more limited. In model systems, energy depletion leads to enhanced mitochondrial integrity, capacity, function and biogenesis but the effects of obesity and weight loss on mitochondria in the human colon are not known. We are using weight loss following bariatric surgery to investigate the effects of altered adiposity on mitochondrial structure and function in human colonocytes. In summary, there is strong and consistent evidence in model systems and more limited evidence in human subjects that over-feeding and/or obesity result in mitochondrial dysfunction and that weight loss might mitigate or reverse some of these effects.

A case-comparison study of pregnant women with mitochondrial disease - what to expect?

OBJECTIVE: Mitochondrial disease is a disorder of energy metabolism that affects 1 in 4300 adults in the UK. Pregnancy is associated with physiological demands that have implications for energy metabolism. We were interested to know how pregnancy was affected in women with mitochondrial disease, particularly those with the most common pathogenic mutation m.3243A>G. DESIGN: Retrospective case-comparison study. POPULATION/SETTING: Sixty-seven women with genetically confirmed mitochondrial disease from the UK Mitochondrial Diseases Cohort and 69 unaffected women participated. METHODS: Participants answered questionnaires regarding each of their pregnancies. Patients were divided into two groups according to genetic mutation, with those harbouring m.3243A>G comprising a single group. MAIN OUTCOME MEASURES: Pregnancy-related complications, mode of delivery, gestational age and birthweight of newborns. RESULTS: Of 139 live births in the comparison group, 62 were in the m.3243A>G group and 87 were in the 'all other mutations' group. Pregnancies of women with the m.3243A>G mutation had significantly more gestational diabetes (odds ratio [OR] = 8.2, 95% CI 1.3-50.1), breathing difficulties (OR = 7.8, 95% CI 1.0-59.1) and hypertension (OR = 8.2, 95% CI 3.1-21.5) than the comparison group. Only half of the pregnancies in the m.3243A>G group had normal vaginal delivery, with emergency caesarean section accounting for 24.2% of deliveries. Babies were born significantly earlier to mothers harbouring m.3243A>G with 53.3% of them preterm (<37 weeks). These babies were also more likely to require resuscitation and admission. CONCLUSION: Women who carried the m.3243A>G mutation appeared to be at higher risk of complications during pregnancies, caesarean section and preterm delivery than the unaffected women or those with other forms of mitochondrial disease. TWEETABLE ABSTRACT: Pregnant women with mitochondrial disease - m.3243A>G mutation - are at greatly increased risk of complications and preterm delivery.

Mitochondrial respiratory chain function and content are preserved in the skeletal muscle of active very old men and women.

INTRODUCTION: The loss of mitochondrial function and content have been implicated in sarcopenia although they have been little studied in the very old, the group in which sarcopenia is most common. In this pilot study, our aim was to determine if mitochondrial respiratory chain function and content are preserved among healthy 85-year-olds. METHODS: We recruited 19 participants (11 female) through their general practitioner and assessed their medical history, functional status and self-reported physical activity. We identified sarcopenia using grip strength, Timed Up-and-Go and bioimpedance analysis. We assessed mitochondrial respiratory chain function using phosphorous magnetic resonance spectroscopy, estimating τ1/2 PCr, the recovery half-time of phosphocreatine in the calf muscles following a bout of aerobic exercise. We performed a biopsy of the vastus lateralis muscle and assessed mitochondrial respiratory chain content by measuring levels of subunits of complex I and IV of the respiratory chain, expressed as Z-scores relative to that in young controls. RESULTS: Participants had a median (IQR) of 2 (1,3) long-term conditions, reported regular aerobic physical activity, and one participant (5.3%) had sarcopenia. Sixteen participants completed the magnetic resonance protocol and the mean (SD) τ1/2 PCr of 35.6 (11.3) seconds was in keeping with preserved mitochondrial function. Seven participants underwent muscle biopsy and the mean fibre Z-scores were -0.7 (0.7) and -0.2 (0.4) for complexes I and IV, respectively, suggesting preserved content of mitochondrial respiratory chain enzymes. CONCLUSION: Muscle mitochondrial respiratory chain function and content are preserved in a sample of active, well-functioning 85-year-olds, among whom sarcopenia was uncommon. The results from this study will help inform future work examining the association between muscle mitochondrial deficiency and sarcopenia.

Review: Central nervous system involvement in mitochondrial disease.

Mitochondrial respiratory chain defects are an important cause of inherited disorders affecting approximately 1 in 5000 people in the UK population. Collectively these disorders are termed 'mitochondrial diseases' and they result from either mitochondrial DNA mutations or defects in nuclear DNA. Although they are frequently multisystem disorders, neurological deficits are particularly common, wide-ranging and disabling for patients. This review details the manifold neurological impairments associated with mitochondrial disease, and describes the efforts to understand how they arise and progressively worsen in patients with mitochondrial disease. We describe advances in our understanding of disease pathogenesis through detailed neuropathological studies and how this has spurred the development of cellular and animal models of disease. We underscore the importance of continued clinical, molecular genetic, neuropathological and animal model studies to fully characterize mitochondrial diseases and understand mechanisms of neurodegeneration. These studies are instrumental for the next phase of mitochondrial research that has a particular emphasis on finding novel ways to treat mitochondrial disease to improve patient care and quality of life.

Potential compounds for the treatment of mitochondrial disease.

INTRODUCTION: Mitochondrial diseases are a group of heterogeneous disorders for which no curative therapy is currently available. Several drugs are currently being pursued as candidates to correct the underlying biochemistry that causes mitochondrial dysfunction. SOURCES OF DATA: A systematic review of pharmacological therapeutics tested using in vitro, in vivo models and clinical trials. Results presented from database searches undertaken to ascertain compounds currently being pioneered to treat mitochondrial disease. AREAS OF AGREEMENT: Previous clinical research has been hindered by poorly designed trials that have shown some evidence in enhancing mitochondrial function but without significant results. AREAS OF CONTROVERSY: Several compounds under investigation display poor pharmacokinetic profiles or numerous off target effects. GROWING POINTS: Drug development teams should continue to screen existing and novel compound libraries for therapeutics that can enhance mitochondrial function. Therapies for mitochondrial disorders could hold potential cures for a myriad of other ailments associated with mitochondrial dysfunction such as neurodegenerative diseases.

Aggregated α-synuclein and complex I deficiency: exploration of their relationship in differentiated neurons.

α-Synuclein becomes misfolded and aggregated upon damage by various factors, for example, by reactive oxygen species. These aggregated forms have been proposed to have differential toxicities and their interaction with mitochondria may cause dysfunction within this organelle that contributes to the pathogenesis of Parkinson's disease (PD). In particular, the association of α-synuclein with mitochondria occurs through interaction with mitochondrial complex I and importantly defects of this protein have been linked to the pathogenesis of PD. Therefore, we investigated the relationship between aggregated α-synuclein and mitochondrial dysfunction, and the consequences of this interaction on cell survival. To do this, we studied the effects of α-synuclein on cybrid cell lines harbouring mutations in either mitochondrial complex I or IV. We found that aggregated α-synuclein inhibited mitochondrial complex I in control and complex IV-deficient cells. However, when aggregated α-synuclein was applied to complex I-deficient cells, there was no additional inhibition of mitochondrial function or increase in cell death. This would suggest that as complex I-deficient cells have already adapted to their mitochondrial defect, the subsequent toxic effects of α-synuclein are reduced.

Initial development and validation of a mitochondrial disease quality of life scale.

Mitochondrial diseases are a clinically diverse group of genetic disorders that often present to neurologists. Health related quality of life (HRQOL) is increasingly recognised as a fundamental patient based outcome measure in both clinical intervention and research. Generic outcome measures have been extensively validated to assess HRQOL across populations and different disease states. However, due to their inclusive construct, it is acknowledged that not all relevant aspects of a specific illness may be captured. Hence there is a need to develop disease specific HRQOL measures that centre on symptoms characteristic of a specific disease or condition and their impact. This study presents the initial conceptualisation, development and preliminary psychometric assessment (validity and reliability) of a mitochondrial disease specific HRQOL measure (Newcastle Mitochondrial Quality of life measure (NMQ)). NMQ is a valuable assessment tool and consists of 63 items within 16 unidimensional domains, each demonstrating good internal reliability (Cronbach's α≥0.83) and construct validity.

Mitochondrial DNA deletions and depletion within paraspinal muscles.

AIMS: Although mitochondrial abnormalities have been reported within paraspinal muscles in patients with axial weakness and neuromuscular disease as well as with ageing, the basis of respiratory deficiency in paraspinal muscles is not known. This study aimed to determine the extent and basis of respiratory deficiency in paraspinal muscles from cases undergoing surgery for degenerative spinal disease and post mortem cases without a history of spinal disease, where age-related histopathological changes were previously reported. METHODS: Cervical and lumbar paraspinal muscles were obtained peri-operatively from 13 patients and from six post mortem control cases (age range 18-82 years) without a neurological disease. Sequential COX/SDH (mitochondrial respiratory chain complex IV/complex II) histochemistry was performed to identify respiratory-deficient muscle fibres (lacking complex IV with intact complex II activity). Real-time polymerase chain reaction, long-range polymerase chain reaction and sequencing were used to identify and characterize mitochondrial DNA (mtDNA) deletions and determine mtDNA copy number status. Mitochondrial respiratory chain complex subunits were detected by immunohistochemistry. RESULTS: The density of respiratory-deficient fibres increased with age. On average, 3.96% of fibres in paraspinal muscles were respiratory-deficient (range 0-10.26). Respiratory deficiency in 36.8% of paraspinal muscle fibres was due to clonally expanded mtDNA deletions. MtDNA depletion accounted for further 13.5% of respiratory deficiency. The profile of immunohistochemically detected subunits of complexes was similar in respiratory-deficient fibres with and without mtDNA deletions or mtDNA depletion. CONCLUSIONS: Paraspinal muscles appeared to be particularly susceptible to age-related mitochondrial respiratory chain defects. Clonally expanded mtDNA deletions and focal mtDNA depletion may contribute towards the development of age-related postural abnormalities.

Mitochondrial disease in pregnancy: a systematic review.

Mitochondrial diseases are heterogeneous in clinical presentation and genotype. The incidence of known pathogenic mitochondrial DNA mutations in the general population is 1 in 500. Little is known about the implications of pregnancy for women with mitochondrial disease. We undertook a systematic review of the literature on mitochondrial disease in pregnancy. Ten case reports were identified. The most common complications were threatened preterm labour (5 women) and preeclampsia (4 women). Two women experienced magnesium sulphate toxicity. Pregnancy had a varied effect on mitochondrial disease with some women being asymptomatic; others developing mild symptoms such as exercise intolerance or muscle weakness which resolved postnatally; and others developed more serious, persistent symptoms such as symptomatic Wolff-Parkinson-White syndrome, persistent paraesthesia and focal segmental glomerulosclerosis. Women with mitochondrial disease appear to be at increased risk of complications during pregnancy and labour but further prospective cohort studies are needed.

The clinical, histochemical, and molecular spectrum of PEO1 (Twinkle)-linked adPEO.

BACKGROUND: Mutations in the Twinkle (PEO1) gene are a recognized cause of autosomal dominant progressive external ophthalmoplegia (adPEO), resulting in the accumulation of multiple mitochondrial DNA (mtDNA) deletions and cytochrome c oxidase (COX)-deficient fibers in skeletal muscle secondary to a disorder of mtDNA maintenance. Patients typically present with isolated extraocular muscle involvement, with little apparent evidence of the clinical heterogeneity documented in other mtDNA maintenance disorders, in particular POLG-related disease. METHODS: We reviewed the clinical, histochemical, and molecular genetics analysis of 33 unreported patients from 26 families together with all previous cases described in the literature to define the clinical phenotype associated with PEO1 mutations. RESULTS: Ptosis and ophthalmoparesis were almost universal clinical features among this cohort, with 52% (17/33) reporting fatigue and 33% (11/33) having mild proximal myopathy. Features consistent with CNS involvement were rarely described; however, in 24% (8/33) of the patients, cardiac abnormalities were reported. Mitochondrial histochemical changes observed in muscle showed remarkable variability, as did the secondary mtDNA deletions, which in some patients were only detected by PCR-based assays and not Southern blotting. Moreover, we report 7 novel PEO1 variants. CONCLUSIONS: Our data suggest a shared clinical phenotype with variable mild multiorgan involvement, and that the contribution of PEO1 mutations as a cause of adPEO may well be underestimated. Direct sequencing of the PEO1 gene should be considered in adPEO patients prior to muscle biopsy.

Multi-system neurological disease is common in patients with OPA1 mutations.

Additional neurological features have recently been described in seven families transmitting pathogenic mutations in OPA1, the most common cause of autosomal dominant optic atrophy. However, the frequency of these syndromal 'dominant optic atrophy plus' variants and the extent of neurological involvement have not been established. In this large multi-centre study of 104 patients from 45 independent families, including 60 new cases, we show that extra-ocular neurological complications are common in OPA1 disease, and affect up to 20% of all mutational carriers. Bilateral sensorineural deafness beginning in late childhood and early adulthood was a prominent manifestation, followed by a combination of ataxia, myopathy, peripheral neuropathy and progressive external ophthalmoplegia from the third decade of life onwards. We also identified novel clinical presentations with spastic paraparesis mimicking hereditary spastic paraplegia, and a multiple sclerosis-like illness. In contrast to initial reports, multi-system neurological disease was associated with all mutational subtypes, although there was an increased risk with missense mutations [odds ratio = 3.06, 95% confidence interval = 1.44-6.49; P = 0.0027], and mutations located within the guanosine triphosphate-ase region (odds ratio = 2.29, 95% confidence interval = 1.08-4.82; P = 0.0271). Histochemical and molecular characterization of skeletal muscle biopsies revealed the presence of cytochrome c oxidase-deficient fibres and multiple mitochondrial DNA deletions in the majority of patients harbouring OPA1 mutations, even in those with isolated optic nerve involvement. However, the cytochrome c oxidase-deficient load was over four times higher in the dominant optic atrophy + group compared to the pure optic neuropathy group, implicating a causal role for these secondary mitochondrial DNA defects in disease pathophysiology. Individuals with dominant optic atrophy plus phenotypes also had significantly worse visual outcomes, and careful surveillance is therefore mandatory to optimize the detection and management of neurological disability in a group of patients who already have significant visual impairment.

Detection of cytochrome c oxidase activity and mitochondrial proteins in single cells.

Cytochrome c oxidase or mitochondrial respiratory chain complex IV is where over 90% of oxygen is consumed. The relationship between complex IV activity and mitochondrial proteins, which provides a guide to understanding the mechanisms in primary mitochondrial disorders, has been determined by histochemistry (activity) and immunohistochemistry in serial sections. In the central nervous system (CNS), mitochondrial activity and immunoreactivity have been determined in populations of cells in serial sections as capturing cells in more than one section is difficult. In this report we describe a method to determine complex IV activity in relation to mitochondrial proteins at a single cell level in the CNS. We performed complex IV histochemistry and immunohistochemistry consecutively in snap frozen sections. Although the product of complex IV histochemistry reduces the sensitivity of standard immunohistochemistry (secondary antibody and ABC method) the biotin-free Menapath polymer detection system (A. Menarini Diagnostics, Wokingham, UK) enables mitochondrial proteins to be detected following complex IV histochemistry. The co-occurring chromogens may then be separately visualised and analysed using multi-spectral imaging (Nuance system CRi, Woburn, MA). Our technique is applicable for exploring mitochondrial defects within single cells in a variety of CNS disorders and animal models of those diseases.

Transmitochondrial embryonic stem cells containing pathogenic mtDNA mutations are compromised in neuronal differentiation.

OBJECTIVES: Defects of the mitochondrial genome (mtDNA) cause a series of rare, mainly neurological disorders. In addition, they have been implicated in more common forms of movement disorders, dementia and the ageing process. In order to try to model neuronal dysfunction associated with mitochondrial disease, we have attempted to establish a series of transmitochondrial mouse embryonic stem cells harbouring pathogenic mtDNA mutations. MATERIALS AND METHODS: Transmitochondrial embryonic stem cell cybrids were generated by fusion of cytoplasts carrying a variety of mtDNA mutations, into embryonic stem cells that had been pretreated with rhodamine 6G, to prevent transmission of endogenous mtDNA. Cybrids were differentiated into neurons and assessed for efficiency of differentiation and electrophysiological function. RESULTS: Neuronal differentiation could occur, as indicated by expression of neuronal markers. Differentiation was impaired in embryonic stem cells carrying mtDNA mutations that caused severe biochemical deficiency. Electrophysiological tests showed evidence of synaptic activity in differentiated neurons carrying non-pathogenic mtDNA mutations or in those that caused a mild defect of respiratory activity. Again, however, neurons carrying mtDNA mutations that resulted in severe biochemical deficiency had marked reduction in post-synaptic events. CONCLUSIONS: Differentiated neurons carrying severely pathogenic mtDNA defects can provide a useful model for understanding how such mutations can cause neuronal dysfunction.

Novel POLG1 mutations associated with neuromuscular and liver phenotypes in adults and children.

BACKGROUND: The POLG1 gene encodes the catalytic subunit of DNA polymerase gamma, essential for mitochondrial DNA replication and repair. Mutations in POLG1 have been linked to a spectrum of clinical phenotypes, and may account for up to 25% of all adult presentations of mitochondrial disease. METHODS AND RESULTS: We present 14 patients, with characteristic features of mitochondrial disease including progressive external ophthalmoplegia (PEO) and Alpers-Huttenlocher syndrome and laboratory findings indicative of mitochondrial dysfunction, including cytochrome c oxidase (COX) deficiency and multiple deletions or depletion of the mitochondrial DNA. Four novel POLG1 missense substitutions (p.R597W, p.L605R, p.G746S, p.A862T), are described, together with the first adult patient with a recently described polymerase domain mutation (p.R1047W). All novel changes were rare in a control population and affected highly conserved amino acids. CONCLUSION: The addition of these substitutions-including the first report of a dinucleotide mutation (c.1814_1815TT>GC)-to the growing list of defects further confirms the importance of POLG1 mutations as the underlying abnormality in a range of neurological presentations.