Simplifying the clinical classification of polymerase gamma (POLG) disease based on age of onset; studies using a cohort of 155 cases.

BACKGROUND: Variants in POLG are one of the most common causes of inherited mitochondrial disease. Phenotypic classification of POLG disease has evolved haphazardly making it complicated and difficult to implement in everyday clinical practise. The aim of our study was to simplify the classification and facilitate better clinical recognition. METHODS: A multinational, retrospective study using data from 155 patients with POLG variants recruited from seven European countries. RESULTS: We describe the spectrum of clinical features associated with POLG variants in the largest known cohort of patients. While clinical features clearly form a continuum, stratifying patients simply according to age of onset-onset prior to age 12 years; onset between 12 and 40 years and onset after the age of 40 years, permitted us to identify clear phenotypic and prognostic differences. Prior to 12 years of age, liver involvement (87%), seizures (84%), and feeding difficulties (84%) were the major features. For those with onset between 12 and 40 years, ataxia (90%), peripheral neuropathy (84%), and seizures (71%) predominated, while for those with onset over 40 years, ptosis (95%), progressive external ophthalmoplegia (89%), and ataxia (58%) were the major clinical features. The earlier the onset the worse the prognosis. Patients with epilepsy and those with compound heterozygous variants carried significantly worse prognosis. CONCLUSION: Based on our data, we propose a simplified POLG disease classification, which can be used to guide diagnostic investigations and predict disease course.

Monogenic Diabetes: Genetics and Relevance on Diabetes Mellitus Personalized Medicine.

BACKGROUND: Diabetes mellitus (DM) is a complex disease with significant impression in today's world. Aside from the most common types recognized over the years, such as type 1 diabetes (T1DM) and type 2 diabetes (T2DM), recent studies have emphasized the crucial role of genetics in DM, allowing the distinction of monogenic diabetes. METHODS: Authors did a literature search with the purpose of highlighting and clarifying the subtypes of monogenic diabetes, as well as the accredited genetic entities responsible for such phenotypes. RESULTS: The following subtypes were included in this literature review: maturity-onset diabetes of the young (MODY), neonatal diabetes mellitus (NDM) and maternally inherited diabetes and deafness (MIDD). So far, 14 subtypes of MODY have been identified, while three subtypes have been identified in NDM - transient, permanent, and syndromic. DISCUSSION: Despite being estimated to affect approximately 2% of all the T2DM patients in Europe, the exact prevalence of MODY is still unknown, accentuating the need for research focused on biomarkers. Consequently, due to its impact in the course of treatment, follow-up of associated complications, and genetic implications for siblings and offspring of affected individuals, it is imperative to diagnose the monogenic forms of DM accurately. CONCLUSION: Currently, advances in the genetics field allowed the recognition of new DM subtypes, which until now, were considered slight variations of the typical forms. Thus, it is imperative to act in the close interaction between genetics and clinical manifestations, to facilitate diagnosis and individualize treatment.

[Mitochondrial DNA depletion syndrome-13: a case with an unusual onset]. / Síndrome de depleción de ADN mitocondrial tipo 13: un caso con un inicio poco común.

TITLE: Síndrome de depleción de ADN mitocondrial tipo 13: un caso con un inicio poco común.

FBXL4 defects are common in patients with congenital lactic acidemia and encephalomyopathic mitochondrial DNA depletion syndrome.

Mutations in FBXL4 have recently been recognized to cause a mitochondrial disorder, with clinical features including early onset lactic acidosis, hypotonia, and developmental delay. FBXL4 sequence analysis was performed in 808 subjects suspected to have a mitochondrial disorder. In addition, 28 samples from patients with early onset of lactic acidosis, but without identifiable mutations in 192 genes known to cause mitochondrial diseases, were examined for FBXL4 mutations. Definitive diagnosis was made in 10 new subjects with a total of 7 novel deleterious variants; 5 null and 2 missense substitutions. All patients exhibited congenital lactic acidemia, most of them with severe encephalopathic presentation, and global developmental delay. Overall, FBXL4 defects account for at least 0.7% (6 out of 808) of subjects suspected to have a mitochondrial disorder, and as high as 14.3% (4 out of 28) in young children with congenital lactic acidosis and clinical features of mitochondrial disease. Including FBLX4 in the mitochondrial diseases panel should be particularly important for patients with congenital lactic acidosis.

Degree of glutathione deficiency and redox imbalance depend on subtype of mitochondrial disease and clinical status.

Mitochondrial disorders are associated with decreased energy production and redox imbalance. Glutathione plays a central role in redox signaling and protecting cells from oxidative damage. In order to understand the consequences of mitochondrial dysfunction on in vivo redox status, and to determine how this varies by mitochondrial disease subtype and clinical severity, we used a sensitive tandem mass spectrometry assay to precisely quantify whole blood reduced (GSH) and oxidized (GSSG) glutathione levels in a large cohort of mitochondrial disorder patients. Glutathione redox potential was calculated using the Nernst equation. Compared to healthy controls (n = 59), mitochondrial disease patients (n = 58) as a group showed significant redox imbalance (redox potential -251 mV ± 9.7, p<0.0001) with an increased level of oxidation by ∼ 9 mV compared to controls (-260 mV ± 6.4). Underlying this abnormality were significantly lower whole blood GSH levels (p = 0.0008) and GSH/GSSG ratio (p = 0.0002), and significantly higher GSSG levels (p<0.0001) in mitochondrial disease patients compared to controls. Redox potential was significantly more oxidized in all mitochondrial disease subgroups including Leigh syndrome (n = 15), electron transport chain abnormalities (n = 10), mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (n = 8), mtDNA deletion syndrome (n = 7), mtDNA depletion syndrome (n = 7), and miscellaneous other mitochondrial disorders (n = 11). Patients hospitalized in metabolic crisis (n = 7) showed the greatest degree of redox imbalance at -242 mV ± 7. Peripheral whole blood GSH and GSSG levels are promising biomarkers of mitochondrial dysfunction, and may give insights into the contribution of oxidative stress to the pathophysiology of the various mitochondrial disorders. In particular, evaluation of redox potential may be useful in monitoring of clinical status or response to redox-modulating therapies in clinical trials.

A mitochondrial implication in a Tunisian patient with Friedreich's ataxia-like.

Genes encoding the DNA helicase TWINKLE (C10orf2) or the two subunits of mtDNA polymerase γ (POLγ) (POLG1 and POLG2) have a direct effect on the mitochondrial DNA replication machinery and were reported in many mitochondrial disorders. Friedreich's ataxia (FRDA) is the common cause of ataxia often associated with the expansion of a GAA repeat in intron 1 of the frataxin gene (FXN). Mitochondrial DNA could be considered as a candidate modifier factor for FRDA disease, since mitochondrial oxidative stress is thought to be involved in the pathogenesis of this disease. We screened the FXN, POLG1 and C10orf2 genes in a Tunisian patient with clinical features of Friedreich's ataxia-like. The results showed the absence of the expansion of a GAA triplet repeat in intron 1 of the FXN gene. Besides, the sequencing of all the exons and their flanking regions of the FXN, POLG1 and C10orf2 genes revealed the presence of intronic polymorphisms. In addition, screening of the mtDNA revealed the presence of several mitochondrial known variations and the absence of mitochondrial deletions in this patient. The detected m.16187C>T and the m.16189T>C change the order of the homopolymeric tract of cytosines between 16184 and 16193 in the mitochondrial D-loop and could lead to a mitochondrial dysfunction by inhibiting replication and affecting protein involved in the replication process of the mtDNA which could be responsible for the clinical features of Friedreich ataxia observed in the studied patient.

Mitochondrial retinal dystrophy associated with the m.3243A>G mutation.

OBJECTIVE: To describe the spectrum of retinal abnormalities associated with the m.3243A>G mutation in the mitochondrial MTTL1 gene and to analyze putative correlations among the severity of retinal abnormalities, disease severity in other organ systems, and heteroplasmy levels. DESIGN: Observational, cohort-based, cross-sectional study. PARTICIPANTS: Twenty-nine patients carrying the m.3243A>G mutation. METHODS: Extensive clinical examinations, including visual acuity testing, indirect ophthalmoscopy, color fundus photography, fundus autofluorescence (FAF), high-resolution optical coherence tomography (OCT), and central visual field analysis. In selected patients, Goldmann perimetry, fluorescein angiography, full-field electroretinography (ERG) and electro-oculography (EOG), and color vision testing were performed. Heteroplasmy levels of the m.3243A>G mutation were measured in leukocytes, urinary epithelial cells (UECs), and buccal mucosa. The Newcastle Mitochondrial Disease Adult Scale (NMDAS) score was measured for all patients. MAIN OUTCOME MEASURES: Age at onset, visual acuity, fundus appearance, FAF, OCT findings, systemic disease features, heteroplasmy levels, and NMDAS scores. RESULTS: Twenty-five of the 29 mutation carriers (86%) had retinal abnormalities that could be classified into 4 grades. Six patients (21%) had grade 1 retinal dystrophy with fine pigment abnormalities that were clearly visible with FAF and fluorescein angiography. Eleven patients (38%) had grade 2 abnormalities that were characterized by yellowish or mildly pigmented deposits in the early stage; in advanced grade 2, these pigment changes encompassed the entire macula and often encircled the optic disc. Six patients (21%) had grade 3 disease in which profound chorioretinal atrophy was present outside the fovea. Two patients (7%) with retinal abnormalities had grade 4 disease, in which the fovea was affected by atrophy, with marked loss of visual acuity. The grade of mitochondrial retinal dystrophy correlated significantly with both age (r = -0.483, P = 0.008) and visual acuity (r = -0.614, P < 0.001), whereas no correlation was observed with heteroplasmy level or overall disease involvement. CONCLUSIONS: Mitochondrial retinal dystrophy associated with the m.3243A>G mutation has specific characteristics that can be classified into 4 grades based on the findings on ophthalmoscopy, FAF, and OCT. However, because the maternal inheritance pattern can be masked and the systemic disease associations can be variable or even absent, the disease may be misdiagnosed.

MitoLSDB: a comprehensive resource to study genotype to phenotype correlations in human mitochondrial DNA variations.

Human mitochondrial DNA (mtDNA) encodes a set of 37 genes which are essential structural and functional components of the electron transport chain. Variations in these genes have been implicated in a broad spectrum of diseases and are extensively reported in literature and various databases. In this study, we describe MitoLSDB, an integrated platform to catalogue disease association studies on mtDNA (http://mitolsdb.igib.res.in). The main goal of MitoLSDB is to provide a central platform for direct submissions of novel variants that can be curated by the Mitochondrial Research Community. MitoLSDB provides access to standardized and annotated data from literature and databases encompassing information from 5231 individuals, 675 populations and 27 phenotypes. This platform is developed using the Leiden Open (source) Variation Database (LOVD) software. MitoLSDB houses information on all 37 genes in each population amounting to 132397 variants, 5147 unique variants. For each variant its genomic location as per the Revised Cambridge Reference Sequence, codon and amino acid change for variations in protein-coding regions, frequency, disease/phenotype, population, reference and remarks are also listed. MitoLSDB curators have also reported errors documented in literature which includes 94 phantom mutations, 10 NUMTs, six documentation errors and one artefactual recombination. MitoLSDB is the largest repository of mtDNA variants systematically standardized and presented using the LOVD platform. We believe that this is a good starting resource to curate mtDNA variants and will facilitate direct submissions enhancing data coverage, annotation in context of pathogenesis and quality control by ensuring non-redundancy in reporting novel disease associated variants.

Mitochondrial disease in childhood: nuclear encoded.

Primary mitochondrial disorders are clinically and genetically heterogeneous, caused by an alteration(s) in either mitochondrial DNA or nuclear DNA, and affect the respiratory chain's ability to undergo oxidative phosphorylation, leading to decreased production of adenosine triphosphophate and subsequent energy failure. These disorders may present at any age, but children tend to have an acute onset of disease compared with subacute or slowly progressive presentation in adults. Varying organ involvement also contributes to the phenotypic spectrum seen in these disorders. The childhood presentation of primary mitochondrial disease is mainly due to nuclear DNA mutations, with mitochondrial DNA mutations being less frequent in childhood and more prominent in adulthood disease. The clinician should be aware of the pediatric presentation of mitochondrial disease and have an understanding of the myriad of nuclear genes responsible for these disorders. The nuclear genes can be best understood by utilizing a classification system of location and function within the mitochondria.

Espectro clínico de pacientes con hallazgos histopatológicos y/o moleculares compatibles con enfermedad mitochondrial / Clinical spectrum of patients with histopathological and/or molecular findings compatible with mitochondrial disease

Objetivo: Describir el espectro clínico de pacientes con diagnóstico definitivo de Enfermedad Mitocondrial, y su correlación con hallazgos bioquímicos, neuroimagenológicos, neuropatológicos, y moleculares. Método: Se revisaron las historias clínicas de pacientes con Enfermedad Mitocondrial evaluados durante el período 1990-2011. Resultados: Se incluyeron 41 pacientes, con una edad media inicial de 3,7 años. Identificamos cuatro grupos:1) Síndromes clásicos (65%): a) MELAS del inglés “Mitochondrial encephalomyopathy, lacticacidosis, and stroke-like episodes”, (diez), b) Síndrome de Leigh (diez) c) Síndrome de Kearns –Sayre (cinco), d) PEO del inglés “Progressive External Ophthalmoplegia” plus (OEP plus) (dos), 2) Miopatía: nueve (21,5%) 3) Encefalomiopatías inespecíficas: cinco (12%). Se realizó biopsia muscular en 37 pacientes. Un 70% evidenció fibras rojo rasgadas, cuatro (10,5%) fibras citocromo oxidasa negativas y ocho (14,7%) incremento de la actividad oxidativa subsarcolemal y en la microscopia electrónica alteraciones del tamaño y número de mitocondrias. En 14 se completaron estudios moleculares: Siete presentaron una mutación puntual A3243G en el ADN mitocondrial (MELAS), un paciente una mutación en el ADN mitocondrial A1351G (Síndrome de Leigh) y un paciente una deleción del ADN mitocondrial (OEP plus). Conclusiones: Se pudo corroborar la existencia en nuestro medio de síndromes asociados a patología mitocondrial tradicionalmente reconocidos. Un grupo de pacientes con encefalomiopatías denominadas inespecíficas presentaron un cuadro clínico variable, hallazgos de laboratorio y de imágenes poco orientadores y fue la sospecha de una enfermedad mitocondrial lo que nos llevó a realizar la biopsia que finalmente fue diagnóstica. Es posible que este grupo sea más numeroso y las limitaciones que implica realizar una biopsia muscular se facilite con los estudios moleculares.

Evaluation of a mitochondrial disease criteria scoring system on mitochondrial encephalomyopathy in Chinese patients.

Due to the complicated clinical features of mitochondrial encephalomyopathy, simplified mitochondrial disease criteria (MDC) have recently been established in Europe. This study evaluated the sensitivity and specificity of this scoring system in Chinese patients. Seventy-eight patients with suspected mitochondrial encephalomyopathy were recruited to be scored by the simplified MDC and were further classified into "possible" (2-4), "probable" (5-7), or "definite" categories (≥8). Significant differences were observed between the total scores in the mitochondrial encephalomyopathy group and the other myopathy group. In the mitochondrial encephalomyopathy group, 73.5% of patients had a score above 8, whereas in the other myopathy group, the "definite" percentage was only 3.2%, suggesting the proposed MDC scoring system has a high sensitivity for diagnosis of mitochondrial encephalomyopathy in China. Moreover, there were significant differences in the clinical scores and imaging portions of the MDC, suggesting that the simplified MDC may distinguish mitochondrial disorder from other multisystem disorders to aid in early diagnosis prior to a muscle biopsy.

[Diagnosis and therapy of mitochondrial diseases]. / Mitochondrialis betegségek diagnosztikája es terápiája.

Mitochondrial diseases are a significant part of neuromuscular diseases. Majority of them is multisystemic disorder. The diagnosis can be established in more and more cases. Beyond the routine neurological examination imaging methods (MRI and MR-spectroscopy) and electrophysiology (EMG, ENG, EEG, evoked potential tests) might be helpful in setting the diagnosis. Raised blood lactate level supports the diagnosis. Muscle biopsy demonstrates mitochondrial abnormalities in the majority of cases. The positivity of genetic tests is low, because the amount of mitochondrial DNA alterations is different in tissues. Therefore other tissue than blood (mainly muscle) is necessary for genetic tests. The other reason is that the respiratory chain is under double -mitochondrial and nuclear - genetic control, and testing the nuclear genes are available only in selected laboratories. The treatment is limited, mainly symptomatic.

Single deletions in mitochondrial DNA--molecular mechanisms and disease phenotypes in clinical practice.

Over 20 years ago single clonal deletions were the first mitochondrial DNA (mtDNA) genetic defects described in association with human disease. Since then very large numbers of children and adults harbouring such deletions have been described and it is clear they are an important cause of human mitochondrial disease. However, there still remain many important challenges in relation to our understanding of mechanisms leading to deletion formation and propagation and in relation to the factors determining the complex and varying relationship between genotype and clinical phenotype. Although multidisciplinary team care is essential and can improve quality of life and outcomes for patients, a definitive molecular treatment for single mtDNA deletions remains an important translational research goal. Patients with mtDNA deletions exhibit a very wide range of different clinical phenotypes with marked variation in age at onset and disease severity. Single mtDNA deletions may enter into the differential diagnosis of many different paediatric and adult presentations across a wide range of medical specialties, although neurological presentations are amongst the most common. In this review, we examine the molecular mechanisms underpinning mtDNA replication and we consider the hypotheses proposed to explain the formation and propagation of single large-scale mtDNA deletions. We also describe the range of clinical features associated with single mtDNA deletions, outline a molecular diagnostic approach and discuss current management including the role of aerobic and resistance exercise training programmes.

Mitochondrial medicine.

Mitochondrial diseases are extremely heterogeneous multisystem disorders predominantly affecting tissues or organs with high oxygen consumption like skeletal muscles, brain, endocrine glands, myocardium, eyes, ears, intestines, liver, kidneys, and bone marrow. Although various clinical syndromes have been described, they frequently overlap and there is no diagnostic gold standard to identify all. It is difficult to chart the future of an affected individual as also to predict the response to treatment which is mostly supportive and symptomatic. The rapidly increasing understanding of the pathophysiologic background of mitochondrial disorders may facilitate diagnostic approach and open perspectives to curative therapies. With the coming of age for mitochondrial medicine, it is now appropriate that physicians keep themselves well-acquainted with the recent developments in this expanding field of biomedical research.

Laminar cortical necrosis in mitochondrial disorders.

OBJECTIVES: Laminar cortical necrosis, defined as focal or diffuse necrosis of one or more cortical lamina, represents an increasingly recognized neuropathological endpoint of vascular, endocrine, immunologic, metabolic, or toxic conditions, of which mitochondrial disorders (MIDs) are the third most frequent after cerebral ischemia and hypoxia. AIMS: To investigate the prevalence of laminar cortical necrosis in MIDs, types of MIDs associated with laminar cortical necrosis, and the morphological characteristics on imaging and autopsy. METHODS: Medline literature review for the terms "laminar cortical necrosis", "cortical signal change", "mitochondrial" and all acronyms of syndromatic MIDs. RESULTS: Among 139 hits for "laminar cortical necrosis", 10 articles fulfilled the inclusion criteria (7%). Among the ten hits five were case series and the other five single case reports. The syndromic MID most frequently associated with laminar cortical necrosis is the MELAS syndrome, but was also described in a single patient each with Leigh syndrome, mitochondrial depletion syndrome, and mitochondrial spinocerebellar ataxia. The morphological and pathohistological features of laminar cortical necrosis in MIDs were not at variance from those in non-mitochondrial disorders. CONCLUSIONS: In MIDs laminar cortical necrosis represents the histopathological and imaging endpoint of a stroke-like lesion. Though laminar cortical necrosis may have a wide pathophysiological background the histological and imaging characteristics do not vary between the different underlying conditions.

Mitochondrial disorders, cognitive impairment and dementia.

The organ most frequently affected in mitochondrial disorders, particularly respiratory chain diseases (RCDs), in addition to the skeletal muscle, is the central nervous system (CNS). CNS manifestations of RCDs comprise stroke-like episodes, epilepsy, migraine, ataxia, spasticity, movement disorders, psychiatric disorders, cognitive decline, or even dementia (mitochondrial dementia). So far mitochondrial dementia has been reported in MELAS, MERRF, LHON, CPEO, KSS, MNGIE, NARP, Leigh syndrome, and Alpers-Huttenlocher disease. Mitochondrial dementia not only results from mutations in the mitochondrial genome but also from mutations in nuclear genes, such as POLG, thymidine kinase 2, or DDP1. Often mitochondrial dementia starts with specific cognitive deficits, particularly in visual construction, attention, abstraction, or flexibility but without a general intellectual deterioration. Cognitive impairment in RCDs is diagnosed upon neuropsychological testing, imaging studies, such as MRI, PET, or MR-spectroscopy, CSF-investigations, or electroencephalography. Therapy of mitochondrial dementia relies on symptomatic measures. Only single patients profit from cholinesterase inhibitors or memantine, antioxidants, vitamins, coenzyme-Q, or other substitutes. Overall, mitochondrial dementia is an important differential of dementias and should be considered in patients with multi-system disease.