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1.
Clin Genet ; 2019 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-31600844

RESUMO

Autosomal dominant progressive external ophthalmoplegia (adPEO) is a late-onset, Mendelian mitochondrial disorder characterised by paresis of the extraocular muscles, ptosis and skeletal-muscle restricted multiple mitochondrial DNA (mtDNA) deletions. While dominantly-inherited, pathogenic variants in POLG, TWNK and RRM2B are among the most common genetic defects of adPEO, identification of novel candidate genes and the underlying pathomechanisms remain challenging. We report the clinical, genetic and molecular investigations of a patient who presented in the seventh decade of life with PEO. Oxidative histochemistry revealed cytochrome c oxidase deficient fibres and occasional ragged red fibres showing subsarcolemmal mitochondrial accumulation in skeletal muscle, while molecular studies identified the presence of multiple mtDNA deletions. Negative candidate screening of known nuclear genes associated with PEO prompted diagnostic exome sequencing, leading to the prioritisation of a novel heterozygous c.547G > C variant in GMPR (NM_006877.3) encoding guanosine monophosphate reductase, a cytosolic enzyme required for maintaining the cellular balance of adenine and guanine nucleotides. We show that the novel c.547G > C variant causes aberrant splicing, decreased GMPR protein levels in patient skeletal muscle, proliferating and quiescent cells and is associated with subtle changes in nucleotide homeostasis protein levels and evidence of disturbed mtDNA maintenance in skeletal muscle. Despite confirmation of GMPR deficiency, demonstrating marked defects of mtDNA replication or nucleotide homeostasis in patient cells proved challenging. Our study proposes that GMPR is the nineteenth (19th) locus for PEO and highlights the complexities of uncovering disease mechanisms in late-onset PEO phenotypes. This article is protected by copyright. All rights reserved.

2.
Ann Clin Transl Neurol ; 6(8): 1487-1497, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31402614

RESUMO

OBJECTIVES: Defining clinically relevant outcome measures for myotonic dystrophy type 1 (DM1) that can be valid and feasible for different phenotypes has proven problematic. The Outcome Measures for Myotonic Dystrophy (OMMYD) group proposed a battery of functional outcomes: 6-minute walk test, 30 seconds sit and stand test, timed 10 m walk test, timed 10 m walk/run test, and nine-hole peg test. This, however, required a large-scale investigation, METHODS: A cohort of 213 patients enrolled in the natural history study, PhenoDM1, was analyzed in cross-sectional analysis and subsequently 98 patients were followed for longitudinal analysis. We aimed to assess: (1) feasibility and best practice; (2) intra-session reliability; (3) validity; and (4) behavior over time, of these tests. RESULTS: OMMYD outcomes proved feasible as 96% of the participants completed at least one trial for all tests and more than half (n = 113) performed all three trials of each test. Body mass index and disease severity associate with functional capacity. There was a significant difference between the first and second trials of each test. There was a moderate to strong correlation between these functional outcomes and muscle strength, disease severity and patient-reported outcomes. All outcomes after 1 year detected a change in functional capacity except the nine-hole peg test. CONCLUSIONS: These tests can be used as a battery of outcomes or independently based on the shown overlapping psychometric features and strong cross-correlations. Due to the large and heterogeneous sample of this study, these results can serve as reference values for future studies.

3.
Ann Neurol ; 86(2): 310-315, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31187502

RESUMO

Distinct clinical syndromes have been associated with pathogenic MT-ATP6 variants. In this cohort study, we identified 125 individuals (60 families) including 88 clinically affected individuals and 37 asymptomatic carriers. Thirty-one individuals presented with Leigh syndrome and 7 with neuropathy ataxia retinitis pigmentosa. The remaining 50 patients presented with variable nonsyndromic features including ataxia, neuropathy, and learning disability. We confirmed maternal inheritance in 39 families and demonstrated that tissue segregation patterns and phenotypic threshold are variant dependent. Our findings suggest that MT-ATP6-related mitochondrial DNA disease is best conceptualized as a mitochondrial disease spectrum disorder and should be routinely included in genetic ataxia and neuropathy gene panels. ANN NEUROL 2019;86:310-315.

4.
Ann Clin Transl Neurol ; 6(5): 826-836, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31139680

RESUMO

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.

6.
Ann Clin Transl Neurol ; 6(3): 515-524, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30911575

RESUMO

Objectives: Mitochondrial methionyl-tRNA formyltransferase (MTFMT) is required for the initiation of translation and elongation of mitochondrial protein synthesis. Pathogenic variants in MTFMT have been associated with Leigh syndrome (LS) and mitochondrial multiple respiratory chain deficiencies. We sought to elucidate the spectrum of clinical, neuroradiological and molecular genetic findings of patients with bi-allelic pathogenic variants in MTFMT. Methods: Retrospective cohort study combining new cases and previously published cases. Results: Thirty-eight patients with pathogenic variants in MTFMT were identified, including eight new cases. The median age of presentation was 14 months (range: birth to 17 years, interquartile range [IQR] 4.5 years), with developmental delay and motor symptoms being the most frequent initial manifestation. Twenty-nine percent of the patients survived into adulthood. MRI headings in MTFMT pathogenic variants included symmetrical basal ganglia changes (62%), periventricular and subcortical white matter abnormalities (55%), and brainstem lesions (48%). Isolated complex I and combined respiratory chain deficiencies were identified in 31% and 59% of the cases, respectively. Reduction of the mitochondrial complex I and complex IV subunits was identified in the fibroblasts (13/13). Sixteen pathogenic variants were identified, of which c.626C>T was the most common. Seventy-four percent of the patients were alive at their last clinical review (median 6.8 years, range: 14 months to 31 years, IQR 14.5 years). Interpretation: Patients that harbour pathogenic variants in MTFMT have a milder clinical phenotype and disease progression compared to LS caused by other nuclear defects. Fibroblasts may preclude the need for muscle biopsy, to prove causality of any novel variant.

7.
Artigo em Inglês | MEDLINE | ID: mdl-30423112

RESUMO

Context: Abnormal growth and short stature are observed in patients with mitochondrial disease but it is unclear whether there is a relationship between final adult height, and disease severity. Objective: To determine whether patients with genetically confirmed mitochondrial disease are shorter than their peers and whether stature is related to disease severity. Design: Analysis of final adult height in relation to disease severity determined by the Newcastle Mitochondrial Disease Adult Scale (NMDAS). Setting: United Kingdom (UK) Mitochondrial Disease Patient Cohort. Patients: 575 patients were identified with recorded height, weight and molecular genetic diagnosis of mitochondrial disease within the UK Mitochondrial Disease Patient Cohort. Main Outcome Measures: Adult Height, BMI and their association with genetic subgroup and disease severity. Results: Adults with mitochondrial disease were short with a mean height of -0.49 standard deviations (SD) (95% CI; -0.58 to -0.39, n=575) compared to UK reference data. Patients were overweight with a BMI SD 0.52 (95% CI; 0.37 to 0.67, n=472). The most common genetic subgroup (m.3243A>G mutation) had a height SD of -0.70 (95% CI; -0.85 to -0.54, n=234) and BMI SD of 0.12 (95% CI; -0.10 to 0.34, n=212). NMDAS scores were negatively correlated with height SD (r= -0.25, 95% CI; -0.33 to -0.17, p<0.001, n=533).Rate of disease progression also correlated negatively with adult height (p<0.001). Conclusion: Final height in mitochondrial disease reflects disease severity and rate of disease progression. Mitochondrial dysfunction and associated subclinical comorbidities affect growth plate physiology.

9.
Hum Mol Genet ; 2018 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-30285085

RESUMO

Recessively-inherited variants in AARS2 (NM_020745.2) encoding mitochondrial alanyl-tRNA synthetase (mt-AlaRS) were first described in patients presenting with fatal infantile cardiomyopathy and multiple oxidative phosphorylation defects. To date, all described patients with AARS2-related fatal infantile cardiomyopathy are united by either a homozygous or compound heterozygous c.1774C>T (p.Arg592Trp) missense founder mutation that is absent in patients with other AARS2-related phenotypes. We describe the clinical, biochemical and molecular investigations of two unrelated boys presenting with fatal infantile cardiomyopathy, lactic acidosis and respiratory failure. Oxidative histochemistry showed cytochrome c oxidase (COX)-deficient fibres in skeletal and cardiac muscle. Biochemical studies showed markedly decreased activities of mitochondrial respiratory chain complexes I and IV with a mild decrease of complex III activity in skeletal and cardiac muscle. Using next-generation sequencing, we identified a c.1738C>T (p.Arg580Trp) AARS2 variant shared by both patients that was in trans with a loss-of-function heterozygous AARS2 variant; a c.1008dupT (p.Asp337*) nonsense variant or an intragenic deletion encompassing AARS2 exons 5-7. Interestingly, our patients did not harbour the p.Arg592Trp AARS2 founder mutation. In silico modelling of the p.Arg580Trp substitution suggested a deleterious impact on protein stability and folding. We confirmed markedly decreased mt-AlaRS protein levels in patient fibroblasts, skeletal and cardiac muscle, although mitochondrial protein synthesis defects were confined to skeletal and cardiac muscle. In vitro data showed that the p.Arg580Trp variant had a minimal effect on activation, aminoacylation or misaminoacylation activities relative to wild-type mt-AlaRS, demonstrating that instability of mt-AlaRS is the biological mechanism underlying the fatal cardiomyopathy phenotype in our patients.

11.
Am J Hum Genet ; 103(2): 221-231, 2018 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-30057030

RESUMO

Bloom syndrome, caused by biallelic mutations in BLM, is characterized by prenatal-onset growth deficiency, short stature, an erythematous photosensitive malar rash, and increased cancer predisposition. Diagnostically, a hallmark feature is the presence of increased sister chromatid exchanges (SCEs) on cytogenetic testing. Here, we describe biallelic mutations in TOP3A in ten individuals with prenatal-onset growth restriction and microcephaly. TOP3A encodes topoisomerase III alpha (TopIIIα), which binds to BLM as part of the BTRR complex, and promotes dissolution of double Holliday junctions arising during homologous recombination. We also identify a homozygous truncating variant in RMI1, which encodes another component of the BTRR complex, in two individuals with microcephalic dwarfism. The TOP3A mutations substantially reduce cellular levels of TopIIIα, and consequently subjects' cells demonstrate elevated rates of SCE. Unresolved DNA recombination and/or replication intermediates persist into mitosis, leading to chromosome segregation defects and genome instability that most likely explain the growth restriction seen in these subjects and in Bloom syndrome. Clinical features of mitochondrial dysfunction are evident in several individuals with biallelic TOP3A mutations, consistent with the recently reported additional function of TopIIIα in mitochondrial DNA decatenation. In summary, our findings establish TOP3A mutations as an additional cause of prenatal-onset short stature with increased cytogenetic SCEs and implicate the decatenation activity of the BTRR complex in their pathogenesis.

13.
Neurology ; 90(21): e1842-e1848, 2018 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-29720545

RESUMO

OBJECTIVE: To describe a patient with a multifocal demyelinating motor neuropathy with onset in childhood and a mutation in phosphatase and tensin homolog (PTEN), a tumor suppressor gene associated with inherited tumor susceptibility conditions, macrocephaly, autism, ataxia, tremor, and epilepsy. Functional implications of this protein have been investigated in Parkinson and Alzheimer diseases. METHODS: We performed whole-exome sequencing in the patient's genomic DNA validated by Sanger sequencing. Immunoblotting, in vitro enzymatic assay, and label-free shotgun proteomic profiling were performed in the patient's fibroblasts. RESULTS: The predominant clinical presentation of the patient was a childhood onset, asymmetric progressive multifocal motor neuropathy. In addition, he presented with macrocephaly, autism spectrum disorder, and skin hamartomas, considered as clinical criteria for PTEN-related hamartoma tumor syndrome. Extensive tumor screening did not detect any malignancies. We detected a novel de novo heterozygous c.269T>C, p.(Phe90Ser) PTEN variant, which was absent in both parents. The pathogenicity of the variant is supported by altered expression of several PTEN-associated proteins involved in tumorigenesis. Moreover, fibroblasts showed a defect in catalytic activity of PTEN against the secondary substrate, phosphatidylinositol 3,4-trisphosphate. In support of our findings, focal hypermyelination leading to peripheral neuropathy has been reported in PTEN-deficient mice. CONCLUSION: We describe a novel phenotype, PTEN-associated multifocal demyelinating motor neuropathy with a skin hamartoma syndrome. A similar mechanism may potentially underlie other forms of Charcot-Marie-Tooth disease with involvement of the phosphatidylinositol pathway.

14.
EMBO Mol Med ; 10(6)2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29735722

RESUMO

Mitochondrial disease associated with the pathogenic m.3243A>G variant is a common, clinically heterogeneous, neurogenetic disorder. Using multiple linear regression and linear mixed modelling, we evaluated which commonly assayed tissue (blood N = 231, urine N = 235, skeletal muscle N = 77) represents the m.3243A>G mutation load and mitochondrial DNA (mtDNA) copy number most strongly associated with disease burden and progression. m.3243A>G levels are correlated in blood, muscle and urine (R2 = 0.61-0.73). Blood heteroplasmy declines by ~2.3%/year; we have extended previously published methodology to adjust for age. In urine, males have higher mtDNA copy number and ~20% higher m.3243A>G mutation load; we present formulas to adjust for this. Blood is the most highly correlated mutation measure for disease burden and progression in m.3243A>G-harbouring individuals; increasing age and heteroplasmy contribute (R2 = 0.27, P < 0.001). In muscle, heteroplasmy, age and mtDNA copy number explain a higher proportion of variability in disease burden (R2 = 0.40, P < 0.001), although activity level and disease severity are likely to affect copy number. Whilst our data indicate that age-corrected blood m.3243A>G heteroplasmy is the most convenient and reliable measure for routine clinical assessment, additional factors such as mtDNA copy number may also influence disease severity.

15.
Pulm Circ ; 8(2): 2045894018768290, 2018 Apr-Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29799315

RESUMO

Mitochondrial dysfunction within the pulmonary vessels has been shown to contribute to the pathology of idiopathic pulmonary arterial hypertension (IPAH). We investigated the hypothesis of whether impaired exercise capacity observed in IPAH patients is in part due to primary mitochondrial oxidative phosphorylation (OXPHOS) dysfunction in skeletal muscle. This could lead to potentially new avenues of treatment beyond targeting the pulmonary vessels. Nine clinically stable participants with IPAH underwent cardiopulmonary exercise testing, in vivo and in vitro assessment of mitochondrial function by 31P-magnetic resonance spectroscopy (31P-MRS) and laboratory muscle biopsy analysis. 31P-MRS showed abnormal skeletal muscle bioenergetics with prolonged recovery times of phosphocreatine and abnormal muscle pH handling. Histochemistry and quadruple immunofluorescence performed on muscle biopsies showed normal function and subunit protein abundance of the complexes within the OXPHOS system. Our findings suggest that there is no primary mitochondrial OXPHOS dysfunction but raises the possibility of impaired oxygen delivery to the mitochondria affecting skeletal muscle bioenergetics during exercise.

16.
J Med Genet ; 55(8): 515-521, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-29602790

RESUMO

BACKGROUND: Thymine kinase 2 (TK2) is a mitochondrial matrix protein encoded in nuclear DNA and phosphorylates the pyrimidine nucleosides: thymidine and deoxycytidine. Autosomal recessive TK2 mutations cause a spectrum of disease from infantile onset to adult onset manifesting primarily as myopathy. OBJECTIVE: To perform a retrospective natural history study of a large cohort of patients with TK2 deficiency. METHODS: The study was conducted by 42 investigators across 31 academic medical centres. RESULTS: We identified 92 patients with genetically confirmed diagnoses of TK2 deficiency: 67 from literature review and 25 unreported cases. Based on clinical and molecular genetics findings, we recognised three phenotypes with divergent survival: (1) infantile-onset myopathy (42.4%) with severe mitochondrial DNA (mtDNA) depletion, frequent neurological involvement and rapid progression to early mortality (median post-onset survival (POS) 1.00, CI 0.58 to 2.33 years); (2) childhood-onset myopathy (40.2%) with mtDNA depletion, moderate-to-severe progression of generalised weakness and median POS at least 13 years; and (3) late-onset myopathy (17.4%) with mild limb weakness at onset and slow progression to respiratory insufficiency with median POS of 23 years. Ophthalmoparesis and facial weakness are frequent in adults. Muscle biopsies show multiple mtDNA deletions often with mtDNA depletion. CONCLUSIONS: In TK2 deficiency, age at onset, rate of weakness progression and POS are important variables that define three clinical subtypes. Nervous system involvement often complicates the clinical course of the infantile-onset form while extraocular muscle and facial involvement are characteristic of the late-onset form. Our observations provide essential information for planning future clinical trials in this disorder.

17.
Ann Clin Transl Neurol ; 5(3): 333-345, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29560378

RESUMO

Objective: The pathogenic mitochondrial DNA m.3243A>G mutation is associated with a wide range of clinical features, making disease prognosis extremely difficult to predict. We aimed to understand the cause of this heterogeneity. Methods: We examined the phenotypic profile of 238 adult m.3243A>G carriers (patients and asymptomatic carriers) from the UK MRC Mitochondrial Disease Patient Cohort using the Newcastle Mitochondrial Disease Adult Scale. We modeled the role of risk factors for the development of specific phenotypes using proportional odds logistic regression. As mitochondria are under the dual control of their own and the nuclear genome, we examined the role of additive nuclear genetic factors in the development of these phenotypes within 46 pedigrees from the cohort. Results: Seizures and stroke-like episodes affect 25% and 17% of patients, respectively; more common features include hearing impairment, gastrointestinal disturbance, psychiatric involvement, and ataxia. Age, age-adjusted blood heteroplasmy levels, and sex are poor predictors of phenotypic severity. Hearing impairment, diabetes, and encephalopathy show the strongest associations, but pseudo-R2 values are low (0.14-0.17). We found a high heritability estimate for psychiatric involvement (h2=0.76, P = 0.0003) and moderate estimates for cognition (h2=0.46, P = 0.0021), ataxia (h2 = 0.45, P = 0.0011), migraine (h2 = 0.41, P = 0.0138), and hearing impairment (h2 = 0.40, P = 0.0050). Interpretation: Our results provide good evidence for the presence of nuclear genetic factors influencing clinical outcomes in m.3234A>G-related disease, paving the way for future work identifying these through large-scale genetic linkage and association studies, increasing our understanding of the pathogenicity of m.3243A>G and providing improved estimates of prognosis.

18.
EBioMedicine ; 30: 86-93, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29506874

RESUMO

Mutations in the m.13094T>C MT-ND5 gene have been previously described in three cases of Leigh Syndrome (LS). In this retrospective, international cohort study we identified 20 clinically affected individuals (13 families) and four asymptomatic carriers. Ten patients were deceased at the time of analysis (median age of death was 10years (range: 5·4months-37years, IQR=17·9years). Nine patients manifested with LS, one with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), and one with Leber hereditary optic neuropathy. The remaining nine patients presented with either overlapping syndromes or isolated neurological symptoms. Mitochondrial respiratory chain activity analysis was normal in five out of ten muscle biopsies. We confirmed maternal inheritance in six families, and demonstrated marked variability in tissue segregation, and phenotypic expression at relatively low blood mutant loads. Neuropathological studies of two patients manifesting with LS/MELAS showed prominent capillary proliferation, microvacuolation and severe neuronal cell loss in the brainstem and cerebellum, with conspicuous absence of basal ganglia involvement. These findings suggest that whole mtDNA genome sequencing should be considered in patients with suspected mitochondrial disease presenting with complex neurological manifestations, which would identify over 300 known pathogenic variants including the m.13094T>C.


Assuntos
Encéfalo/patologia , Complexo I de Transporte de Elétrons/genética , Proteínas Mitocondriais/genética , Mutação/genética , Adolescente , Adulto , Encéfalo/diagnóstico por imagem , Criança , Estudos de Coortes , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Síndrome , Adulto Jovem
19.
Epilepsia Open ; 3(1): 103-108, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29588995

RESUMO

Focal status epilepticus in POLG-related mitochondrial disease is highly refractory to pharmacological agents, including general anesthesia. We report the challenges in managing a previously healthy teenager who presented with de novo epilepsia partialis continua and metabolic stroke resulting from the homozygous p.Ala467Thr POLG mutation, the most common pathogenic variant identified in the Caucasian population. We applied transcranial direct current stimulation (tDCS; 2 mA; 20 min) daily as an adjunctive therapy because her focal seizures failed to respond to five antiepileptic drugs at maximal doses. The electrical and clinical seizures stopped after 3 days of tDCS. The second course of tDCS was administered for 14 days when the focal seizures re-emerged a month later. The patient tolerated the procedure well. Following 4 months of hospitalization and prolonged community rehabilitation, our patient has now returned to full-time education with support, and there is no report of cognitive deficit. We have demonstrated the safety and efficacy of tDCS in treating refractory focal motor seizures caused by mitochondrial disease.

20.
New Bioeth ; 24(1): 57-73, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29529980

RESUMO

The development of any novel reproductive technology involving manipulation of human embryos is almost inevitably going to be controversial and evoke sincerely held, but diametrically opposing views. The plethora of scientific, ethical and legal issues that surround the clinical use of such techniques fuels this divergence of opinion. During the policy change that was required to allow the use of mitochondrial donation in the UK, many of these issues were intensely scrutinised by a variety of people and in multiple contexts. This extensive process resulted in the publication of several reports that informed the recommendations made to government. We have been intrinsically involved in the development of mitochondrial donation, from refining the basic technique for use in human embryos through to clinical service delivery, and have taken the opportunity in this article to offer our own perspective on the issues it raises.


Assuntos
Temas Bioéticos , Doenças Mitocondriais/terapia , Terapia de Substituição Mitocondrial , Pesquisa , Dissidências e Disputas , Humanos , Mitocôndrias , Política Pública , Serviços de Saúde Reprodutiva , Técnicas Reprodutivas/ética , Reino Unido
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