Metabolic myopathies: update 2009

Cardiac phenotype in adolescents and young adults with long-chain 3-hydroxyacyl CoA dehydrogenase (LCHAD) deficiency

PURPOSE

Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency (LCHADD) is a rare fatty acid oxidation disorder characterized by recurrent episodes of metabolic decompensation and rhabdomyolysis, as well as retinopathy, peripheral neuropathy, and cardiac involvement, such as infantile dilated cardiomyopathy. Because LCHADD patients are surviving longer, we sought to characterize LCHADD-associated major cardiac involvement in adolescence and young adulthood.

METHODS

A retrospective cohort of 16 adolescent and young adult participants with LCHADD was reviewed for cardiac phenotype.

RESULTS

Major cardiac involvement occurred in 9 of 16 participants, including sudden death, out-of-hospital cardiac arrest, acute cardiac decompensations with heart failure and/or in-hospital cardiac arrest, end-stage dilated cardiomyopathy, and moderate restrictive cardiomyopathy. Sudden cardiac arrest was more common in males and those with a history of infant cardiomyopathy.

CONCLUSION

The cardiac manifestations of LCHADD in adolescence and early adulthood are complex and distinct from the phenotype seen in infancy. Life-threatening arrhythmia occurs at substantial rates in LCHADD, often in the absence of metabolic decompensation or rhabdomyolysis. The potential risk factors identified here-male sex and history of infant cardiomyopathy-may hint at strategies for risk stratification and possibly the prevention of these events.

ACTA1 H40Y mutant iPSC-derived skeletal myocytes display mitochondrial defects in an in vitro model of nemaline myopathy

Nemaline myopathies (NM) are a group of congenital myopathies that lead to muscle weakness and dysfunction. While 13 genes have been identified to cause NM, over 50% of these genetic defects are due to mutations in nebulin (NEB) and skeletal muscle actin (ACTA1), which are genes required for normal assembly and function of the thin filament. NM can be distinguished on muscle biopsies due to the presence of nemaline rods, which are thought to be aggregates of the dysfunctional protein. Mutations in ACTA1 have been associated with more severe clinical disease and muscle weakness. However, the cellular pathogenesis linking ACTA1 gene mutations to muscle weakness are unclear To evaluate cellular disease phenotypes, iPSC-derived skeletal myocytes (iSkM) harboring an ACTA1 H40Y point mutation were used to model NM in skeletal muscle. These were generated by Crispr-Cas9, and include one non-affected healthy control (C) and 2 NM iPSC clone lines, therefore representing isogenic controls. Fully differentiated iSkM were characterized to confirm myogenic status and subject to assays to evaluate nemaline rod formation, mitochondrial membrane potential, mitochondrial permeability transition pore (mPTP) formation, superoxide production, ATP/ADP/phosphate levels and lactate dehydrogenase release. C- and NM-iSkM demonstrated myogenic commitment as evidenced by mRNA expression of Pax3, Pax7, MyoD, Myf5 and Myogenin; and protein expression of Pax4, Pax7, MyoD and MF20. No nemaline rods were observed with immunofluorescent staining of NM-iSkM for ACTA1 or ACTN2, and these mRNA transcript and protein levels were comparable to C-iSkM. Mitochondrial function was altered in NM, as evidenced by decreased cellular ATP levels and altered mitochondrial membrane potential. Oxidative stress induction revealed the mitochondrial phenotype, as evidenced by collapsed mitochondrial membrane potential, early formation of the mPTP and increased superoxide production. Early mPTP formation was rescued with the addition of ATP to media. Together, these findings suggest that mitochondrial dysfunction and oxidative stress are disease phenotypes in the in vitro model of ACTA1 nemaline myopathy, and that modulation of ATP levels was sufficient to protect NM-iSkM mitochondria from stress-induced injury. Importantly, the nemaline rod phenotype was absent in our in vitro model of NM. We conclude that this in vitro model has the potential to recapitulate human NM disease phenotypes, and warrants further study.

Elderly onset of MELAS in a male: A case report

BACKGROUND

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) is one of the most common maternally inherited mitochondrial diseases which rarely affects elderly people.

CASE PRESENTATION

We reported the case of a 61-year-old male patient with MELAS. He was experiencing acute migraine-like headaches as the first symptoms. Laboratory data showed elevated lactate and creatine kinase levels. Brain magnetic resonance imaging (MRI) found a high signal intensity lesion in the left occipital-temporal-parietal lobe on diffusion-weighted imaging (DWI). Magnetic resonance angiography (MRA) revealed reversible vasoconstriction of the middle cerebral arteries and superficial temporal arteries. A muscle biopsy suggested minor muscle damage. A genetic study revealed a mitochondrial DNA A3243G mutation.

CONCLUSION

Elderly onset of MELAS is rare and easily misdiagnosed as an ischemic stroke. MELAS with the onset of stroke-like episodes should be considered in adult or elderly patients with imaging findings that are atypical for cerebral infarction. The use of multimodal MRI in the clinical diagnosis of MELAS could be extremely beneficial.

Neuropsychological Features of Children and Adolescents With Mitochondrial Disorders: A Descriptive Case Series

BACKGROUND

Mitochondrial disorders (MD) are metabolic diseases related to genetic mutations in mitochondrial DNA and nuclear DNA that cause dysfunction of the mitochondrial respiratory chain. Cognitive impairment and psychiatric symptoms are frequently associated with MD in the adult population. The aim of this study is to describe the neuropsychological profile in children and adolescents with MD.

METHODS

We prospectively recruited a sample of 12 children and adolescents between February 2019 and February 2020 in the Reference Center for Mitochondrial Disorders of Angers (France). Participants and their parents completed an anamnestic form describing socio-demographic data and completed the WISC-V (Wechsler Intelligence Scale for Children, 5th edition) and the Parent and Teacher forms of the BRIEF (Behavior Rating Inventory of Executive Function).

RESULTS

In our sample, the mean IQ (Intellectual Quotient) score was 87.3 ± 25.3. The score ranged from 52 to 120. Concerning executive functions, a significant global clinical complaint was found for parents (six times more than normal) and to a lesser extent, for teachers (among 3 to 4 times more). Levels of intelligence and executive functioning were globally linked in our cohort but dissociation remains a possibility.

CONCLUSION

The results of this study show that MD can be associated to neuropsychological disorders in children and adolescents, especially regarding the intelligence quotient and the executive function. Our study also highlights the need for regular neuropsychological assessments in individuals with MD and developing brains, such as children and adolescents.

[Chronic Fatigue: When to Suspect an Inherited Metabolic Disease?]

Chronic Fatigue: When to Suspect an Inherited Metabolic Disease? Abstract. Chronic fatigue is a non-specific symptom, frequent in outpatient adults' consultations. Persistent physical fatigue of unknown etiology should prompt the search for rare diseases including inherited metabolic disorder (IMD) after elimination of common causes. The main characteristic of chronic fatigue in IMD is its dynamic nature, worsened by circumstances leading to an increased metabolism such as physical exertion, cold, fasting or infection. IMD leading to chronic fatigue are metabolic myopathies, in particular glycogen storage disease affecting muscle, fatty acid oxidation disorders and mitochondrial diseases. The diagnosis is confirmed by specific biochemical and/or molecular analyzes with multidisciplinary management.

[Chronic Fatigue: When to Suspect an Inherited Metabolic Disease?]

Chronic Fatigue: When to Suspect an Inherited Metabolic Disease? Abstract. Chronic fatigue is a non-specific symptom, frequent in outpatient adults' consultations. Persistent physical fatigue of unknown etiology should prompt the search for rare diseases including inherited metabolic disorder (IMD) after elimination of common causes. The main characteristic of chronic fatigue in IMD is its dynamic nature, worsened by circumstances leading to an increased metabolism such as physical exertion, cold, fasting or infection. IMD leading to chronic fatigue are metabolic myopathies, in particular glycogen storage disease affecting muscle, fatty acid oxidation disorders and mitochondrial diseases. The diagnosis is confirmed by specific biochemical and/or molecular analyzes with multidisciplinary management.

Diaphragmatic dysfunction in neuromuscular disease, an MRI study

The aim of this exploratory study was to evaluate diaphragmatic function across various neuromuscular diseases using spirometry-controlled MRI. We measured motion of the diaphragm relative to that of the thoracic wall (cranial-caudal ratio vs. anterior posterior ratio; CC-AP ratio), and changes in the diaphragmatic curvature (diaphragm height and area ratio) during inspiration in 12 adults with a neuromuscular disease having signs of respiratory muscle weakness, 18 healthy controls, and 35 adult Pompe patients - a group with prominent diaphragmatic weakness. CC-AP ratio was lower in patients with myopathies (n=7, 1.25±0.30) and motor neuron diseases (n=5, 1.30±0.10) than in healthy controls (1.37±0.14; p=0.001 and p=0.008), but not as abnormal as in Pompe patients (1.12±0.18; p=0.011 and p=0.024). The mean diaphragm height ratio was 1.17±0.33 in patients with myopathies, pointing at an insufficient diaphragmatic contraction. This was also seen in patients with Pompe disease (1.28±0.36), but not in healthy controls (0.82±0.33) or patients with motor neuron disease (0.82±0.24). We conclude that spirometry-controlled MRI enables us to investigate respiratory dysfunction across neuromuscular diseases, suggesting that the diaphragm is affected in a different way in myopathies and motor neuron diseases. Whether MRI can also be used to evaluate progression of diaphragmatic dysfunction requires additional studies.

Glycogen storage disease type XII; an ultra rare cause of hemolytic anemia and rhabdomyolysis: one new case report

OBJECTIVES

Aldolase A deficiency also known as glycogen storage disease (GSD) XII, is an ultra rare autosomal recessively inherited GSD, associated with hemolytic anemia and rhabdomyolysis.

CASE PRESENTATION

Here, we first report a patient with dermatological findings, hemodialysis requirement for rhabdomyolysis, and a novel likely pathogenic c.971C>T (p.A324V) mutation in the ALDOA gene.

CONCLUSIONS

Episodes of rhabdomyolysis can be triggered by febrile illnesses and catabolic processes. Diagnosis should be confirmed by the mutation analysis of ALDOA gene. Treatment includes management of hemolytic anemia and administration of antipyretics during febrile episodes to avoid hemolysis and rhabdomyolysis.

Diagnosis of primary mitochondrial disorders -Emphasis on myopathological aspects

Mitochondrial disorders are one of the most common neurometabolic disorders affecting all age groups. The phenotype-genotype heterogeneity in these disorders can be attributed to the dual genetic control on mitochondrial functions, posing a challenge for diagnosis. Though the advancement in the high-throughput sequencing and other omics platforms resulted in a "genetics-first" approach, the muscle biopsy remains the benchmark in most of the mitochondrial disorders. This review focuses on the myopathological aspects of primary mitochondrial disorders. The utility of muscle biopsy is not limited to analyse the structural abnormalities; rather it also proves to be a potential tool to understand the deranged sub-cellular functions.

Psychiatric Symptoms of Children and Adolescents With Mitochondrial Disorders: A Descriptive Case Series

Background: Mitochondrial disorders (MD) are a group of clinically heterogeneous genetic disorders resulting from dysfunction of the mitochondrial respiratory chain. Cognitive impairment is a common feature in adults with MD and psychiatric symptoms are associated with MD in up to 70% of the adult population. The aim of this study is to describe the psychiatric profile in children and adolescents with MD by focusing on the description of psychiatric symptoms. Methods: A cohort of 12 children and adolescents was prospectively recruited between February 2019 and February 2020 in the Reference Center for Mitochondrial Disorders of Angers (France). Participants and their parents completed an anamnestic form to provide socio-demographic data and completed the Global Assessment of Functioning scale, the Brief Psychiatric Rating Scale, the Child Depression Inventory, the Revised Children's Manifest Anxiety Scale, and the Conner's Rating Scale to evaluate the inattention/hyperactivity symptoms as well as the Quality of Life scale. Results: Four children (33.3%) were diagnosed with depressive symptoms. With regarding to anxiety, 6 children (50%) reported anxiety issues during the psychiatric interview and 3 children (25%) were suffering from anxiety according to the RCMAS scale. Compared to other children with chronic illnesses, the individuals in our cohort reported a lower overall quality of life score and lower scores in physical and social subscales. Conclusion: Our study shows that MD can lead to psychiatric disorders in children and adolescents, in particular anxiety and depression, as well as poor quality of life. This highlights the need for regular psychiatric assessments in individuals with developing brains, such as children and adolescents. We do not, however, have data regarding the neuropsychological profile of this population.

Bezafibrate activation of PPAR drives disturbances in mitochondrial redox bioenergetics and decreases the viability of cells from patients with VLCAD deficiency

Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency is the most common inborn long-chain fatty acid oxidation (FAO) disorder. VLCAD deficiency is characterized by distinct phenotypes. The severe phenotypes are potentially life-threatening and affect the heart or liver, with a comparatively milder phenotype characterized by myopathic symptoms. There is an unmet clinical need for effective treatment options for the myopathic phenotype. The molecular mechanisms driving the gradual decrease in mitochondrial function and associated alterations of muscle fibers are unclear. The peroxisome proliferator-activated receptor (PPAR) pan-agonist bezafibrate is a potent modulator of FAO and multiple other mitochondrial functions and has been proposed as a potential medication for myopathic cases of long-chain FAO disorders. In vitro experiments have demonstrated the ability of bezafibrate to increase VLCAD expression and activity. However, the outcome of small-scale clinical trials has been controversial. We found VLCAD deficient patient fibroblasts to have an increased oxidative stress burden and deranged mitochondrial bioenergetic capacity, compared to controls. Applying heat stress under fasting conditions to bezafibrate pretreated patient cells, caused a marked further increase of mitochondrial superoxide levels. Patient cells failed to maintain levels of the essential thiol peptide antioxidant glutathione and experienced a decrease in cellular viability. Our findings indicate that chronic PPAR activation is a plausible initiator of long-term pathogenesis in VLCAD deficiency. Our findings further implicate disruption of redox homeostasis as a key pathogenic mechanism in VLCAD deficiency and support the notion that a deranged thiol metabolism might be an important pathogenic factor in VLCAD deficiency.

Neuropsychological and Psychiatric Features of Children and Adolescents Affected With Mitochondrial Diseases: A Systematic Review

Mitochondrial diseases (MDs) are a group of clinically heterogeneous genetic disorders that arise as the result of dysfunctional mitochondria. Only few medical articles deal with neuropsychological or psychiatric aspects of MDs.

AIM

The present article aims to provide a systematic review of neuropsychological and psychiatric aspects of MDs.

METHODS

In order to identify all studies dealing with psychiatric and neuropsychological aspects of MDs in children and adolescents, we performed a search in the medical literature between April 2009 and April 2019 using PubMed, Cochrane, and Web of Science and we defined inclusion and exclusion criteria.

RESULTS

We found only seven studies that satisfy the inclusion requirements and criteria. The main psychiatric aspects reported in MDs were depressive and behavioral disorders. With regard to the neuropsychological aspects of MDs, developmental analyses showed an overall deterioration and developmental delay.

INTERPRETATION

Children and adolescents with MDs may present psychiatric symptoms and neuropsychological impairment. A more systematic investigation of psychiatric and neuropsychological features of MDs is needed to foster a better understanding of the phenotype of these diseases and their links with the genotype, which may have significant implications for the developmental trajectories of patients.

Disorders of the Diaphragm

Pathologic processes that involve the central nervous system, phrenic nerve, neuromuscular junction, and skeletal muscle can impair diaphragm function. When these processes are of sufficient severity to cause diaphragm dysfunction, respiratory failure may be a consequence. This article reviews basic diaphragm anatomy and physiology and then discusses diagnostic and therapeutic approaches to disorders that result in unilateral or bilateral diaphragm dysfunction. This discussion provides a context in which disorders of the diaphragm and their implications on respiratory function can be better appreciated.

Conserving wildlife in a changing world: Understanding capture myopathy-a malignant outcome of stress during capture and translocation

The number of species that merit conservation interventions is increasing daily with ongoing habitat destruction, increased fragmentation and loss of population connectivity. Desertification and climate change reduce suitable conservation areas. Physiological stress is an inevitable part of the capture and translocation process of wild animals. Globally, capture myopathy-a malignant outcome of stress during capture operations-accounts for the highest number of deaths associated with wildlife translocation. These deaths may not only have considerable impacts on conservation efforts but also have direct and indirect financial implications. Such deaths usually are indicative of how well animal welfare was considered and addressed during a translocation exercise. Importantly, devastating consequences on the continued existence of threatened and endangered species succumbing to this known risk during capture and movement may result. Since first recorded in 1964 in Kenya, many cases of capture myopathy have been described, but the exact causes, pathophysiological mechanisms and treatment for this condition remain to be adequately studied and fully elucidated. Capture myopathy is a condition with marked morbidity and mortality that occur predominantly in wild animals around the globe. It arises from inflicted stress and physical exertion that would typically occur with prolonged or short intense pursuit, capture, restraint or transportation of wild animals. The condition carries a grave prognosis, and despite intensive extended and largely non-specific supportive treatment, the success rate is poor. Although not as common as in wildlife, domestic animals and humans are also affected by conditions with similar pathophysiology. This review aims to highlight the current state of knowledge related to the clinical and pathophysiological presentation, potential treatments, preventative measures and, importantly, the hypothetical causes and proposed pathomechanisms by comparing conditions found in domestic animals and humans. Future comparative strategies and research directions are proposed to help better understand the pathophysiology of capture myopathy.

Perspectives on Exertional Rhabdomyolysis

Exertional (exercise-induced) rhabdomyolysis is a potentially life threatening condition that has been the subject of research, intense discussion, and media attention. The causes of rhabdomyolysis are numerous and can include direct muscle injury, unaccustomed exercise, ischemia, extreme temperatures, electrolyte abnormalities, endocrinologic conditions, genetic disorders, autoimmune disorders, infections, drugs, toxins, and venoms. The objective of this article is to review the literature on exertional rhabdomyolysis, identify precipitating factors, and examine the role of the dietary supplement creatine monohydrate. PubMed and SPORTDiscus databases were searched using the terms rhabdomyolysis, muscle damage, creatine, creatine supplementation, creatine monohydrate, and phosphocreatine. Additionally, the references of papers identified through this search were examined for relevant studies. A meta-analysis was not performed. Although the prevalence of rhabdomyolysis is low, instances still occur where exercise is improperly prescribed or used as punishment, or incomplete medical history is taken, and exertional rhabdomyolysis occurs. Creatine monohydrate does not appear to be a precipitating factor for exertional rhabdomyolysis. Healthcare professionals should be able to recognize the basic signs of exertional rhabdomyolysis so prompt treatment can be administered. For the risk of rhabdomyolysis to remain low, exercise testing and prescription must be properly conducted based on professional standards.

Metabolic myopathies: a practical approach

Metabolic myopathies are a diverse group of rare genetic disorders and their associated muscle symptoms may be subtle. Patients may present with indolent myopathic features, exercise intolerance or recurrent rhabdomyolysis. Diagnostic delays are common and clinicians need a high index of suspicion to recognise and differentiate metabolic myopathies from other conditions that present in a similar fashion. Standard laboratory tests may be normal or non-specific, particularly between symptomatic episodes. Targeted enzyme activity measurement and next-generation genetic sequencing are increasingly used. There are now specific enzyme replacement therapies available, and other metabolic strategies and gene therapies are undergoing clinical trials. Here, we discuss our approach to the adult patient with suspected metabolic myopathy. We outline key features in the history and examination and discuss some mimics of metabolic myopathies. We highlight some disorders of glycogen and fatty acid utilisation that present in adulthood and outline current recommendations on management.

AMPD3 is associated with the malignant characteristics of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors of the gastrointestinal tract. It is well known that activating mutations in the receptor tyrosine kinases KIT and platelet-derived growth factor receptor-α have essential roles in the pathogenesis of GISTs. The activation of these receptor protein kinases triggers multiple signaling pathways that promote cell proliferation and survival; however, the exact mechanism by which the activation of these kinases promotes the progression of GISTs remains uncertain. The aim of the present was to search for genes that are associated with the progression of GIST. The present study used reverse transcription-quantitative polymerase chain reaction to demonstrate that adenosine monophosphate deaminase 3 (AMPD3) was highly expressed in GISTs. Furthermore, transfection of GIST-T1 cells with KIT-specific small interfering RNA (siRNA) demonstrated that the expression of AMPD3 was dependent on KIT expression, while the depletion of AMPD3 in human GIST-T1 cells using AMPD3-specific siRNA resulted in the suppression of cell migration and invasion. In addition, AMPD3 depletion sensitized GIST-T1 cells to the tyrosine kinase inhibitor imatinib. The results of the present suggested that the combined inhibition of tyrosine kinases and AMPD3 may be effective for the treatment of GISTs.

Progress in Diagnosing Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like Episodes

Objective:

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a progressive, multisystem affected mitochondrial disease associated with a number of disease-related defective genes. MELAS has unpredictable presentations and clinical course, and it can be commonly misdiagnosed as encephalitis, cerebral infarction, or brain neoplasms. This review aimed to update the diagnosis progress in MELAS, which may provide better understanding of the disease nature and help make the right diagnosis as well.

Data Sources:

The data used in this review came from published peer review articles from October 1984 to October 2014, which were obtained from PubMed. The search term is “MELAS”.

Study Selection:

Information selected from those reported studies is mainly based on the progress on clinical features, blood biochemistry, neuroimaging, muscle biopsy, and genetics in diagnosing MELAS.

Results:

MELAS has a wide heterogeneity in genetics and clinical manifestations. The relationship between mutations and phenotypes remains unclear. Advanced serial functional magnetic resonance imaging (MRI) can provide directional information on this disease. Muscle biopsy has meaningful value in diagnosing MELAS, which shows the presence of ragged red fibers and mosaic appearance of cytochrome oxidase negative fibers. Genetic studies have reported that approximately 80% of MELAS cases are caused by the mutation m.3243A>G of the mitochondrial transfer RNA (Leu (UUR)) gene (MT-TL1).

Conclusions:

MELAS involves multiple systems with variable clinical symptoms and recurrent episodes. The prognosis of MELAS patients depends on timely diagnosis. Therefore, overall diagnosis of MELAS should be based on the maternal inheritance family history, clinical manifestation, and findings from serial MRI, muscle biopsy, and genetics.

Proteome Profiling and Ultrastructural Characterization of the Human RCMH Cell Line: Myoblastic Properties and Suitability for Myopathological Studies

Studying (neuro)muscular disorders is a major topic in biomedicine with a demand for suitable model systems. Continuous cell culture (in vitro) systems have several technical advantages over in vivo systems and became widely used tools for discovering physiological/pathophysiological mechanisms in muscle. In particular, myoblast cell lines are suitable model systems to study complex biochemical adaptations occurring in skeletal muscle and cellular responses to altered genetic/environmental conditions. Whereas most in vitro studies use extensively characterized murine C2C12 cells, a comprehensive description of an equivalent human cell line, not genetically manipulated for immortalization, is lacking. Therefore, we characterized human immortal myoblastic RCMH cells using scanning (SEM) and transmission electron microscopy (TEM) and proteomics. Among more than 6200 identified proteins we confirm the known expression of proteins important for muscle function. Comparing the RCMH proteome with two well-defined nonskeletal muscle cells lines (HeLa, U2OS) revealed a considerable enrichment of proteins important for muscle function. SEM/TEM confirmed the presence of agglomerates of cytoskeletal components/intermediate filaments and a prominent rough ER. In conclusion, our results indicate RMCH as a suitable in vitro model for investigating muscle function-related processes such as mechanical stress burden and mechanotransduction, EC coupling, cytoskeleton, muscle cell metabolism and development, and (ER-associated) myopathic disorders.

Muscle Ultrasound in Patients with Glycogen Storage Disease Types I and III

In glycogen storage diseases (GSDs), improved longevity has resulted in the need for neuromuscular surveillance. In 12 children and 14 adults with the "hepatic" (GSD-I) and "myopathic" (GSD-III) phenotypes, we cross-sectionally assessed muscle ultrasound density (MUD) and muscle force. Children with both "hepatic" and "myopathic" GSD phenotypes had elevated MUD values (MUD Z-scores: GSD-I > 2.5 SD vs. GSD-III > 1 SD, p < 0.05) and muscle weakness (GSD-I muscle force; p < 0.05) of myopathic distribution. In "hepatic" GSD-I adults, MUD stabilized (GSD-I adults vs. GSD-I children, not significant), concurring with moderate muscle weakness (GSD-I adults vs. healthy matched pairs, p < 0.05). In "myopathic" GSD-III adults, MUD increased with age (MUD-GSD III vs. age: r = 0.71-0.83, GSD-III adults > GSD-III children, p < 0.05), concurring with pronounced muscle weakness (GSD-III adults vs. GSD-I adults, p < 0.05) of myopathic distribution. Children with "hepatic" and "myopathic" GSD phenotypes were both found to have myopathy. Myopathy stabilizes in "hepatic" GSD-I adults, whereas it progresses in "myopathic" GSD-III adults. Muscle ultrasonography provides an excellent, non-invasive tool for neuromuscular surveillance per GSD phenotype.

Feeding and Swallowing Disorders in Pediatric Neuromuscular Diseases: An Overview

Feeding and swallowing problems in infants and children have a great impact on health and wellbeing. The aim of this study was to provide an overview of recognized feeding and swallowing problems in different groups of children with neuromuscular diseases, based on relevant literature and expert opinion, and to propose recommendations for the assessment and treatment of these problems. Almost all pediatric neuromuscular diseases are accompanied by feeding and swallowing problems during the different phases of deglutition, problems that give rise to a wide variety of signs and symptoms, which emphasizes the importance of a comprehensive feeding and swallowing assessment by a speech and language therapist.

A diagnostic approach to recurrent myalgia and rhabdomyolysis in children

Episodic myalgia is a common complaint in children and young adults. While many cases remain idiopathic even after extensive investigation, myalgia can be the first symptom of an underlying serious neuromuscular condition, and can be associated with an increased risk of such serious complications as rhabdomyolysis and malignant hyperthermia. We review and highlight the metabolic myopathies and other increasingly recognised muscle disorders that may present to paediatricians with episodic myalgia or isolated episodes of rhabdomyolysis, and propose a diagnostic algorithm for investigation of these complaints.

Lactate and Energy Metabolism During Exercise in Patients With Blocked Glycogenolysis (McArdle Disease)

CONTEXT

Patients with blocked muscle glycogen breakdown (McArdle disease) have severely reduced exercise capacity compared to healthy individuals and are not assumed to produce lactate during exercise.

OBJECTIVES

The objectives were: 1) to quantify systemic and muscle lactate kinetics and oxidation rates and muscle energy utilization during exercise in patients with McArdle disease; and 2) to elucidate the role of lactate formation in muscle energy production.

DESIGN AND SETTING

This was a single trial in a hospital.

PARTICIPANTS

Participants were four patients with McArdle disease and seven healthy subjects.

INTERVENTION

Patients and healthy controls were studied at rest, which was followed by 40 minutes of cycle-ergometer exercise at 60% of the patients' maximal oxygen uptake (∼35 W).

MAIN OUTCOME MEASURES

Main outcome measures were systemic and leg skeletal muscle lactate, alanine, fatty acid, and glucose kinetics.

RESULTS

McArdle patients had a marked decrease in plasma lactate concentration at the onset of exercise, and the concentration remained suppressed during exercise. A substantial leg net lactate uptake and subsequent oxidation occurred over the entire exercise period in patients, in contrast to a net lactate release or no exchange in the healthy controls. Despite a net lactate uptake by the active leg, a simultaneous unidirectional lactate release was observed in McArdle patients at rates that were similar to the healthy controls.

CONCLUSION

Lactate is an important energy source for contracting skeletal muscle in patients with myophosphorylase deficiency. Although McArdle patients had leg net lactate consumption, a simultaneous release of lactate was observed at rates similar to that found in healthy individuals exercising at the same very low workload, suggesting that lactate formation is mandatory for muscle energy generation during exercise.

Acute rhabdomyolysis and inflammation

Rhabdomyolysis results from the rapid breakdown of skeletal muscle fibers, which leads to leakage of potentially toxic cellular content into the systemic circulation. Acquired causes by direct injury to the sarcolemma are most frequent. The inherited causes are: i) metabolic with failure of energy production, including mitochondrial fatty acid ß-oxidation defects, LPIN1 mutations, inborn errors of glycogenolysis and glycolysis, more rarely mitochondrial respiratory chain deficiency, purine defects and peroxysomal α-methyl-acyl-CoA-racemase defect (AMACR), ii) structural causes with muscle dystrophies and myopathies, iii) calcium pump disorder with RYR1 gene mutations, iv) inflammatory causes with myositis. Irrespective of the cause of rhabdomyolysis, the pathology follows a common pathway, either by the direct injury to sarcolemma by increased intracellular calcium concentration (acquired causes) or by the failure of energy production (inherited causes), which leads to fiber necrosis. Rhabdomyolysis are frequently precipitated by febrile illness or exercise. These conditions are associated with two events, elevated temperature and high circulating levels of pro-inflammatory mediators such as cytokines and chemokines. To illustrate these points in the context of energy metabolism, protein thermolability and the potential benefits of arginine therapy, we focus on a rare cause of rhabdomyolysis, aldolase A deficiency. In addition, our studies on lipin-1 (LPIN1) deficiency raise the possibility that several diseases involved in rhabdomyolysis implicate pro-inflammatory cytokines and may even represent primarily pro-inflammatory diseases. Thus, not only thermolability of mutant proteins critical for muscle function, but also pro-inflammatory cytokines per se, may lead to metabolic decompensation and rhabdomyolysis.

Induction of Neuron-Specific Degradation of Coenzyme A Models Pantothenate Kinase-Associated Neurodegeneration by Reducing Motor Coordination in Mice

BACKGROUND

Pantothenate kinase-associated neurodegeneration, PKAN, is an inherited disorder characterized by progressive impairment in motor coordination and caused by mutations in PANK2, a human gene that encodes one of four pantothenate kinase (PanK) isoforms. PanK initiates the synthesis of coenzyme A (CoA), an essential cofactor that plays a key role in energy metabolism and lipid synthesis. Most of the mutations in PANK2 reduce or abolish the activity of the enzyme. This evidence has led to the hypothesis that lower CoA might be the underlying cause of the neurodegeneration in PKAN patients; however, no mouse model of the disease is currently available to investigate the connection between neuronal CoA levels and neurodegeneration. Indeed, genetic and/or dietary manipulations aimed at reducing whole-body CoA synthesis have not produced a desirable PKAN model, and this has greatly hindered the discovery of a treatment for the disease.

OBJECTIVE, METHODS, RESULTS AND CONCLUSIONS

Cellular CoA levels are tightly regulated by a balance between synthesis and degradation. CoA degradation is catalyzed by two peroxisomal nudix hydrolases, Nudt7 and Nudt19. In this study we sought to reduce neuronal CoA in mice through the alternative approach of increasing Nudt7-mediated CoA degradation. This was achieved by combining the use of an adeno-associated virus-based expression system with the synapsin (Syn) promoter. We show that mice with neuronal overexpression of a cytosolic version of Nudt7 (scAAV9-Syn-Nudt7cyt) exhibit a significant decrease in brain CoA levels in conjunction with a reduction in motor coordination. These results strongly support the existence of a link between CoA levels and neuronal function and show that scAAV9-Syn-Nudt7cyt mice can be used to model PKAN.

The investigation and management of metabolic myopathies

Metabolic myopathies (MM) are rare inherited primary muscle disorders that are mainly due to abnormalities of muscle energy metabolism resulting in skeletal muscle dysfunction. These diseases include disorders of fatty acid oxidation, glyco(geno)lytic muscle disorders and mitochondrial respiratory chain (MRC) disease. Clinically these disorders present with a range of symptoms including infantile hypotonia, myalgia/exercise tolerance, chronic or acute muscle weakness, cramps/spasms/stiffness or episodic acute rhabdomyolysis. The precipitant may be fasting, infection, general anaesthesia, heat/cold or most commonly, exercise. However, the differential diagnosis includes a wide range of both acquired and inherited conditions and these include exposure to drugs/toxins, inflammatory myopathies, dystrophies and channelopathies. Streamlining of existing diagnostic protocols has now become a realistic prospect given the availability of second-generation sequencing. A diagnostic pathway using a ‘rhabdomyolysis’ gene panel at an early stage of the diagnostic process is proposed. Following detailed clinical evaluation and first-line investigations, some patients will be identified as candidates for McArdle disease/glycogen storage disease type V or MRC disease and these will be referred directly to the specialised services. However, for the majority of patients, second-line investigation is best undertaken through next-generation sequencing using a ‘rhabdomyolysis’ gene panel. Following molecular analysis and careful evaluation of the findings, some patients will receive a clear diagnosis. Further functional or specific targeted testing may be required in other patients to evaluate the significance of uncertain/equivocal findings. For patients with no clear diagnosis, further investigations will be required through a specialist centre.

McArdle disease does not affect skeletal muscle fibre type profiles in humans

Patients suffering from glycogen storage disease V (McArdle disease) were shown to have higher surface electrical activity in their skeletal muscles when exercising at the same intensity as their healthy counterparts, indicating more muscle fibre recruitment. To explain this phenomenon, this study investigated whether muscle fibre type is shifted towards a predominance in type I fibres as a consequence of the disease. Muscle biopsies from the Biceps brachii (BB) (n = 9) or Vastus lateralis (VL) (n = 8) were collected over a 13-year period from male and female patients diagnosed with McArdle disease, analysed for myosin heavy chain (MHC) isoform content using SDS-PAGE, and compared to healthy controls (BB: n = 3; VL: n = 10). All three isoforms were expressed and no difference in isoform expression in VL was found between the McArdle patients and healthy controls (MHC I: 33±19% vs. 43±7%; MHC IIa: 52±9% vs. 40±7%; MHC IIx: 15±18% vs. 17±9%). Similarly, the BB isoform content was also not different between the two groups (MHC I: 33±14% vs. 30±11%; MHC IIa: 46±17% vs. 39±5%; MHC IIx: 21±13% vs. 31±14%). In conclusion, fibre type distribution does not seem to explain the higher surface EMG in McArdle patients. Future studies need to investigate muscle fibre size and contractility of McArdle patients.

A thermolabile aldolase A mutant causes fever-induced recurrent rhabdomyolysis without hemolytic anemia

Aldolase A deficiency has been reported as a rare cause of hemolytic anemia occasionally associated with myopathy. We identified a deleterious homozygous mutation in the ALDOA gene in 3 siblings with episodic rhabdomyolysis without hemolytic anemia. Myoglobinuria was always triggered by febrile illnesses. We show that the underlying mechanism involves an exacerbation of aldolase A deficiency at high temperatures that affected myoblasts but not erythrocytes. The aldolase A deficiency was rescued by arginine supplementation in vitro but not by glycerol, betaine or benzylhydantoin, three other known chaperones, suggesting that arginine-mediated rescue operated by a mechanism other than protein chaperoning. Lipid droplets accumulated in patient myoblasts relative to control and this was increased by cytokines, and reduced by dexamethasone. Our results expand the clinical spectrum of aldolase A deficiency to isolated temperature-dependent rhabdomyolysis, and suggest that thermolability may be tissue specific. We also propose a treatment for this severe disease.

Presumed mitochondrial disease manifesting with recurrent syncopes

OBJECTIVES

Loss of consciousness may be due to neurological or cardiac involvement in mitochondrial disease, and is often difficult to attribute to either cause, as in the following case.

CASE REPORT

A 67-year-old man with hypertension, diabetes, elevated serum creatine kinase, glaucoma, optic atrophy, and vertigo had experienced recurrent losses of consciousness since 63 years of age. Diagnostic work-up revealed paroxysmal supraventricular arrhythmias, hyperlipidemia, steatosis hepatis, renal insufficiency, polyneuropathy, first-degree atrio-ventricular block, orthostasis, and cataract. From the age of 66 years, he developed tonic-clonic seizures. Electrocardiography loop recording showed some losses of consciousness as associated with supraventricular tachycardias and others with epileptic activity or arterial hypotension. Neurological investigations and muscle biopsy were indicative of mitochondrial disease with multisystem involvement. Losses of consciousness disappeared after catheter ablation and treatment with levetiracetam.

CONCLUSION

Recurrent loss of consciousness in mitochondrial disease may not only be due to arrhythmias but also seizure activity, or autonomic neuropathy. Arrhythmias, seizures, and polyneuropathy may have a common underlying cause affecting various tissues.

Metabolic myopathies

PURPOSE OF REVIEW

The metabolic myopathies result from inborn errors of metabolism affecting intracellular energy production due to defects in glycogen, lipid, adenine nucleotides, and mitochondrial metabolism. This article provides an overview of the most common metabolic myopathies.

RECENT FINDINGS

Our knowledge of metabolic myopathies has expanded rapidly in recent years, providing us with major advances in the detection of genetic and biochemical defects. New and improved diagnostic tools are now available for some of these disorders, and targeted therapies for specific biochemical deficits have been developed (ie, enzyme replacement therapy for acid maltase deficiency).

SUMMARY

The diagnostic approach for patients with suspected metabolic myopathy should start with the recognition of a static or dynamic pattern (fixed versus exercise-induced weakness). Individual presentations vary according to age of onset and the severity of each particular biochemical dysfunction. Additional clinical clues include the presence of multisystem disease, family history, and laboratory characteristics. Appropriate investigations, timely treatment, and genetic counseling are discussed for the most common conditions.

Clinical and biological features at diagnosis in mitochondrial fatty acid beta-oxidation defects: a French pediatric study of 187 patients

INTRODUCTION

Mitochondrial fatty acid β-oxidation defects (FAODs) are a group of severe inherited metabolic diseases, most of which can be treated with favorable prognosis following diagnosis. A description of the broad range of phenotypes resulting from these defects remains incomplete, and for this study, we sought to investigate the semiology at diagnosis in a country without a newborn screening program for FAODs.

METHODS

Using a retrospective French multicentre study, we analyzed 187 children aged <6 years at diagnosis with FAOD confirmed by enzymatic and/or molecular analyses. Clinical and biological parameters at diagnosis were assessed to screen liver, heart, neurological, and muscle symptoms. Information concerning the long-term prognosis was also collected.

RESULTS

Predominant hepatic symptoms were observed in 89 % of patients regardless of the underlying defect. The most frequent symptoms observed were hepatomegaly (92 %), increased blood alanine aminotransferase (ALAT) level (82 %), and steatosis (88 %). Other frequent features included Reye syndrome (49 %), increased gamma-glutamyltranspeptidase (GGT) (37 %), and liver failure (27 %). Extrahepatic features were often associated in the foreground. Hypoglycemia (75 %), neurological (64 %), muscle (61 %), or cardiac features (55 %) [as either cardiomyopathy (47 %) or arrhythmias (31 %)] were frequently documented. Hemodynamic events (41 %) were represented by shock (31 %) or sudden death (35 %). Hyperammonemia (73 %) and hyperlactacidemia (57 %) were the two main biochemical features. Total, very-long-chain acyl-CoA dehydrogenase (VLCADD), long-chain 3-hydroxyacylCoA dehydrogenase (LCHADD), and medium-chain acyl-CoA dehydrogenase (MCADD) deficiency mortality rates were 48 %, 60 %, 63 %, and 20 % respectively.

CONCLUSION

This study presents clinical features of a large cohort of patients with FAODs in a country without neonatal screening for FAODs. Our results highlight liver as the main organ involved at diagnosis regardless of age at diagnosis, classical phenotype (i.e., cardiac, hepatic, or muscular), or enzyme deficiency. Although steatosis may be observed in various inherited metabolic defects, it is a reliable indicator of FAOD and should prompt systematic screening when the diagnosis is suspected. The poor long-term prognoses reported are a strong argument for inclusion of FAODs in newborn screening programs.

Carnitine palmitoyltransferase 1C deficiency causes motor impairment and hypoactivity

Carnitine palmitoyltransferase 1c (CPT1C), a brain-specific protein localized in the endoplasmic reticulum of neurons, is expressed in almost all brain regions, but its only known functions to date are involved in the hypothalamic control of energy homeostasis and in hippocampus-dependent spatial learning. To identify other physiological and behavioral functions of this protein, we performed a battery of neurological tests on Cpt1c-deficient mice. The animals showed intact autonomic and sensory systems, but some motor disturbances were observed. A more detailed study of motor function revealed impaired coordination and gait, severe muscle weakness, and reduced daily locomotor activity. Analysis of motor function in these mice at ages of 6-24 weeks showed that motor disorders were already present in young animals and that impairment increased progressively with age. Analysis of CPT1C expression in different motor brain areas during development revealed that CPT1C levels were low from birth to postnatal day 10 and then rapidly increased peaking at postnatal day 21, which suggests that CPT1C plays a relevant role in motor function during and after weaning. As CPT1C is known to regulate ceramide levels, we measured these biolipids in different motor areas in adult mice. Cerebellar, striatum, and motor cortex extracts from Cpt1c knockout mice showed reduced levels of ceramide and its derivative sphingosine when compared to wild-type animals. Our results indicate that altered ceramide metabolism in motor brain areas induced by Cpt1c deficiency causes progressive motor dysfunction from a young age.

Peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1)- and estrogen-related receptor (ERR)-induced regulator in muscle 1 (Perm1) is a tissue-specific regulator of oxidative capacity in skeletal muscle cells

Mitochondrial oxidative metabolism and energy transduction pathways are critical for skeletal and cardiac muscle function. The expression of genes important for mitochondrial biogenesis and oxidative metabolism are under the control of members of the peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1) family of transcriptional coactivators and the estrogen-related receptor (ERR) subfamily of nuclear receptors. Perturbations in PGC-1 and/or ERR activities have been associated with alterations in capacity for endurance exercise, rates of muscle atrophy, and cardiac function. The mechanism(s) by which PGC-1 and ERR proteins regulate muscle-specific transcriptional programs is not fully understood. We show here that PGC-1α and ERRs induce the expression of a so far uncharacterized muscle-specific protein, PGC-1- and ERR-induced regulator in muscle 1 (Perm1), which regulates the expression of selective PGC-1/ERR target genes. Perm1 is required for the basal as well as PGC-1α-enhanced expression of genes with roles in glucose and lipid metabolism, energy transfer, and contractile function. Silencing of Perm1 in cultured myotubes compromises respiratory capacity and diminishes PGC-1α-induced mitochondrial biogenesis. Our findings support a role for Perm1 acting downstream of PGC-1α and ERRs to regulate muscle-specific pathways important for energy metabolism and contractile function. Elucidating the function of Perm1 may enable novel approaches for the treatment of disorders with compromised skeletal muscle bioenergetics, such as mitochondrial myopathies and age-related/disease-associated muscle atrophies.

Fatty Acid oxidation disorders in a chinese population in taiwan

BACKGROUND

Fatty acid oxidation (FAO) disorders are a heterogeneous group of inborn errors in the transportation and oxidation of fatty acids. FAO disorders were thought to be very rare in the Chinese population. Newborn screening for FAO disorders beginning in 2002 in Taiwan may have increased the diagnosis of this group of diseases.

MATERIALS AND METHODS

Till 2012, the National Taiwan University Hospital Newborn Screening Center screened more than 800,000 newborns for FAO disorders. Both patients diagnosed through screening and patients detected after clinical manifestations were included in this study.

RESULTS

A total of 48 patients with FAO disorders were identified during the study period. The disorders included carnitine palmitoyltransferase I deficiency, carnitine acylcarnitine translocase deficiency, carnitine palmitoyltransferase II deficiency, very long-chain acyl-CoA dehydrogenase deficiency, medium-chain acyl-CoA dehydrogenase deficiency, multiple acyl-CoA dehydrogenase deficiency, short-chain defects, and carnitine uptake defect. Thirty-nine patients were diagnosed through newborn screening. Five false-negative newborn screening cases were noted during this period, and four patients who were not screened were diagnosed based on clinical manifestations. The ages of all patients ranged from 6 months to 22.9 years (mean age 6.6 years). Except for one case of postmortem diagnosis, there were no other mortalities.

CONCLUSIONS

The combined incidence of FAO disorders estimated by newborn screening in the Chinese population in Taiwan is 1 in 20,271 live births. Newborn screening also increases the awareness of FAO disorders and triggers clinical diagnoses of these diseases.

Genetic polymorphisms associated with exertional rhabdomyolysis

Exertional rhabdomyolysis (ER) occurs in young, otherwise healthy, individuals principally during strenuous exercise, athletic, and military training. Although many risk factors have been offered, it is unclear why some individuals develop ER when participating in comparable levels of physical exertion under identical environmental conditions and others do not. This study investigated possible genetic polymorphisms that might help explain ER. DNA samples derived from a laboratory-based study of persons who had never experienced an episode of ER (controls) and clinical ER cases referred for testing over the past several years were analyzed for single nucleotide polymorphisms (SNPs) in candidate genes. These included angiotensin I converting enzyme (ACE), α-actinin-3 (ACTN3), creatine kinase muscle isoform (CKMM), heat shock protein A1B (HSPA1B), interleukin 6 (IL6), myosin light chain kinase (MYLK), adenosine monophosphate deaminase 1 (AMPD1), and sickle cell trait (HbS). Population included 134 controls and 47 ER cases. The majority of ER cases were men (n = 42/47, 89.4 %); the five women with ER were Caucasian. Eighteen African Americans (56.3 %) were ER cases. Three SNPs were associated with ER: CKMM Ncol, ACTN3 R577X, and MYLK C37885A. ER cases were 3.1 times more likely to have the GG genotype of CKMM (odds ratio/OR = 3.1, confidence interval/CI 1.33-7.10), 3.0 times for the XX genotype of ACTN3 SNP (OR = 2.97, CI 1.30-3.37), and 5.7 times for an A allele of MYLK (OR = 21.35, CI 2.60-12.30). All persons with HbS were also ER cases. Three distinct polymorphisms were associated with ER. Further work will be required to replicate these findings and determine the mechanism(s) whereby these variants might confer susceptibility.

Noninflammatory myopathies

The noninflammatory myopathies are a diverse group of diseases, some of which may mimic the autoimmune-mediated idiopathic inflammatory myopathies in their clinical presentation. They include certain metabolic, toxic, and infectious myopathies, as well as muscular dystrophies. In addition to muscle weakness, these forms of myopathy may present with exercise intolerance and muscle pain. Special testing techniques are often required to establish the diagnosis. This review focuses on those noninflammatory myopathies that should be included in the differential diagnosis of idiopathic inflammatory myopathy.

Metabolite measurements in the caudate nucleus, anterior cingulate cortex and hippocampus among patients with mitochondrial disorders: a case-control study using proton magnetic resonance spectroscopy

BACKGROUND

Mitochondrial disorders are clinical syndromes associated with mutations in the mitochondrial or nuclear genome that result in impaired oxidative phosphorylation and deficient energy production. Metabolic abnormalities in brain areas associated with cognitive functions could give rise to neuropsychiatric symptomatology. The aim of this study was to use single-voxel proton magnetic resonance spectroscopy to identify metabolic abnormalities in regions implicated in neuropsychiatric symptoms in patients with mitochondrial disorders.

METHODS

N-acetyl-aspartate and creatine levels were measured in the caudate nucleus, anterior cingulate cortex and hippocampus in 15 patients with mitochondrial disorders compared with 15 healthy controls matched for age and sex.

RESULTS

N-acetyl-aspartate levels were significantly lower in the caudate nucleus among patients with mitochondrial disorders (mean 7.04 ± 1.19 standard deviation [SD] institutional units) compared with healthy controls (mean 8.19 ± 1.18 SD institutional units; p = 0.02). Creatine levels were lower in the caudate nucleus among patients compared with controls (patients: mean 6.84 ± 1.42 SD institutional units; controls: mean 7.52 ± 0.76 SD institutional units; p = 0.03), but the results were no longer significant after correction for multiple comparisons. There were no significant differences in metabolite measurements between patients and controls in the anterior cingulate cortex and the hippocampus.

INTERPRETATION

Metabolic abnormalities were identified exclusively in the caudate nucleus, with significantly lower N-acetyl-aspartate levels among patients compared with controls. These results suggest that the corpus striatum may be highly susceptible to mitochondrial oxidative phosphorylation defects and resultant cell loss. Given the role of the caudate nucleus in cognitive and executive functions, our findings raise the possibility that metabolic abnormalities in the caudate nucleus may contribute to cognitive impairment and neuropsychiatric symptoms in patients with mitochondrial disorders, which could be investigated in future studies.

Psychiatric symptoms correlate with metabolic indices in the hippocampus and cingulate in patients with mitochondrial disorders

There is increasing recognition that mitochondrial dysfunction may have a critical role in the pathophysiology of major psychiatric illnesses. Patients with mitochondrial disorders offer a unique window through which we can begin to understand the association between psychiatric symptoms and mitochondrial dysfunction in vivo. Using proton magnetic resonance spectroscopy ((1)H-MRS), we investigated metabolic indices in mitochondrial patients in regions of the brain that have been implicated in psychiatric illness: the caudate, cingulate cortex and hippocampus. In all, 15 patients with mitochondrial disorders and 15 age- and sex-matched controls underwent a comprehensive psychiatric assessment, including the administration of standardized psychiatric rating scales, followed by single voxel (1)H-MRS of the caudate, cingulate cortex and hippocampus to measure N-acetyl aspartate (NAA), creatine (Cr), glycerophosphocholine (GPC), myoinositol and glutamate+glutamine (Glx). Pearson's correlation coefficients were used to determine correlations between metabolites and the psychiatric rating scales. Anxiety symptoms in these patients correlated with higher GPC, Glx, myoinositol and Cr in the hippocampus. Impaired level of function as a result of psychiatric symptoms correlated with higher Glx and GPC in the cingulate cortex. In summary, we found remarkably consistent, and statistically significant, correlations between anxiety and metabolic indices in the hippocampus in patients with mitochondrial disorders, while overall impairment of functioning due to psychiatric symptoms correlated with metabolic markers in the cingulate cortex. These findings lend support to the notion that mitochondrial dysfunction in specific brain regions can give rise to psychiatric symptoms. In particular, they suggest that metabolic processes in the hippocampus may have an important role in the neurobiology of anxiety.

Study of LPIN1, LPIN2 and LPIN3 in rhabdomyolysis and exercise-induced myalgia

BACKGROUND

Recessive LPIN1 mutations were identified as a cause of severe rhabdomyolysis in pediatric patients. The human lipin family includes two other closely related members, lipin-2 and 3, which share strong homology and similar activity. The study aimed to determine the involvement of the LPIN family genes in a cohort of pediatric and adult patients (n = 171) presenting with muscular symptoms, ranging from severe (CK >10 000 UI/L) or moderate (CK <10 000 UI/L) rhabdomyolysis (n = 141) to exercise-induced myalgia (n = 30), and to report the clinical findings in patients harboring mutations.

METHODS

Coding regions of LPIN1, LPIN2 and LPIN3 genes were sequenced using genomic or complementary DNAs.

RESULTS

Eighteen patients harbored two LPIN1 mutations, including a frequent intragenic deletion. All presented with severe episodes of rhabdomyolysis, starting before age 6 years except two (8 and 42 years). Few patients also suffered from permanent muscle symptoms, including the eldest ones (≥ 40 years). Around 3/4 of muscle biopsies showed accumulation of lipid droplets. At least 40% of heterozygous relatives presented muscular myalgia. Nine heterozygous SNPs in LPIN family genes were identified in milder phenotypes (mild rhabdomyolysis or myalgia). These variants were non-functional in yeast complementation assay based on respiratory activity, except the LPIN3-P24L variant.

CONCLUSION

LPIN1-related myolysis constitutes a major cause of early-onset rhabdomyolysis and occasionally in adults. Heterozygous LPIN1 mutations may cause mild muscular symptoms. No major defects of LPIN2 or LPIN3 genes were associated with muscular manifestations.

Exercise testing in metabolic myopathies

Metabolic myopathies are a group of genetic disorders specifically affecting glucose/glycogen, lipid, and mitochondrial metabolism. The main metabolic myopathies that are evaluated in this article are the mitochondrial myopathies, fatty acid oxidation defects, and glycogen storage disease. This article focuses on the usefulness of exercise in the evaluation of genetic metabolic myopathies.

Multidisciplinary management of an obstetric patient with glycogen storage disease type 3

A 22-year-old primiparous woman with known glycogen storage disease type 3a presented to our hospital during her 12th week of pregnancy. Glycogen storage disease type 3 is a rare inherited disorder resulting from a deficiency of the glycogen debranching enzyme, causing the accumulation of abnormal short-chain glycogen in liver, blood cells, myocardium and striated muscle. Symptoms improve after puberty but the increased metabolism of pregnancy predisposes to hypoglycaemia, ketosis and lactic acidosis. Cardiomyopathy, distal weakness and peripheral neuropathy may present after the third decade. The patient was managed antenatally with regular cornflour feeds and was scheduled for elective caesarean delivery. She presented in early labour at 38 weeks and delivered a healthy neonate by urgent caesarean delivery under spinal anaesthesia. Intravenous dextrose infusion and regular blood glucose monitoring were used during the perinatal period to prevent hypoglycaemia. An arterial line was inserted in the operating room for frequent blood sampling and to avoid muscle cramps which could be induced by the intermittent inflation of the automated blood pressure cuff. Obstetric, anaesthetic and neonatal outcomes were uneventful.

Six novel mutations in the myophosphorylase gene in patients with McArdle disease and a family with pseudo-dominant inheritance pattern

McArdle disease is an autosomal recessive glycogenosis due to deficiency of the enzyme myophosphorylase. It results from homozygous or compound heterozygous mutations in the gene for this enzyme, PYGM. We report six novel mutations in the PYGM gene based upon sequencing data including three missense mutations (p.D51G, p.P398L, and p.N648Y), one nonsense mutation (p.Y75X), one frame-shift mutation (p.Y114SfsX181), and one amino acid deletion (p.Y53del) in six patients with McArdle disease. We also report on a Caucasian family that appeared to transmit McArdle disease in an autosomal dominant manner. In order to evaluate the potential pathogenicity of the sequence variants, we performed in silico analysis using PolyPhen-2 and SIFT BLink, along with species conservation analysis using UCSC Genome Browser. The above mutations were all predicted to be disease associated with high probability and with at least the same level of certainty as several confirmed mutations. The current data add to the list of pathogenic mutations in the PYGM gene associated with McArdle disease.

Potassium-aggravated muscle stiffness in 12 cats

CASE DESCRIPTION

12 European shorthair cats (6 males and 6 females; age range, 2 months to 3 years) from 1 household were evaluated for clinical signs of recurrent and progressive muscle spasticity. Genetic relationships among the cats were suspected but were not known.

CLINICAL FINDINGS

Physical examination of all cats revealed a thin to mildly emaciated body condition and signs of suppurative rhinitis. Results of neurologic evaluations revealed no abnormalities in any cats at rest, but exercise- and stress-induced episodes of muscle spasticity were observed. Results of hematologic (7/12 cats) and CSF (4) analysis, diagnostic imaging (including radiography [7] and magnetic resonance imaging [4]), electromyography (4), motor nerve conduction tests (4), screening for metabolic storage diseases (4), provocation tests via exercise in a cold (4°C [39.2°F]) environment (7), and gross pathological and histologic examination (5) revealed no abnormalities that could potentially explain the clinical signs. However, consumption of a potassium-enriched diet resulted in severe aggravation of clinical signs in 7 of 7 cats, leading to a diagnosis of potassium-aggravated muscle stiffness.

TREATMENT AND OUTCOME

5 cats were euthanized after initial examination because of poor physical condition and severe clinical signs. Spasticity in the 7 remaining cats was improved during a 6-week follow-up period as they reduced their own activity. Further investigation and treatment were declined.

CLINICAL RELEVANCE

Channelopathies are rarely recognized diseases in domestic animals. In addition to conventional diagnostic evaluation methods, provocation tests in a clinical environment can be used in the assessment of channelopathies.

Essential muscle pathology for the rheumatologist

This review introduces/refreshes some basic histopathologic methods and findings of skeletal muscle biopsies with emphasis on those diseases commonly encountered in a rheumatologist's practice. The 3 general areas of myopathology discussed are metabolic myopathies, toxic myopathies, and inflammatory myopathies. The authors, neuropathologists, hope to provide in this article what they think are some commonalities and disease-specific methods in their pathologic workup as well as a practical approach to the collaboration that pathologists undertake with their rheumatology colleagues to come to a working diagnosis.

Creatine as a therapeutic strategy for myopathies

Myopathies are genetic or acquired disorders of skeletal muscle that lead to varying degrees of weakness, atrophy, and exercise intolerance. In theory, creatine supplementation could have a number of beneficial effects that could enhance function in myopathy patients, including muscle mass, strength and endurance enhancement, lower calcium levels, anti-oxidant effects, and reduced apoptosis. Patients with muscular dystrophy respond to several months of creatine monohydrate supplementation (~0.075-0.1 g/kg/day) with greater strength (~9%) and fat-free mass (~0.63 kg). Patients with myotonic dystrophy do not show as consistent an effect, possibly due to creatine transport issues. Creatine monohydrate supplementation shows modest benefits only at lower doses and possibly negative effects (cramping) at higher doses in McArdle's disease patients. Patients with MELAS syndrome show some evidence of benefit from creatine supplementation in exercise capacity, with the effects in patients with CPEO being less robust, again, possibly due to limited muscle creatine uptake. The evidence for side effects or negative impact upon serological metrics from creatine supplementation in all groups of myopathy patients is almost non-existent and pale in comparison to the very substantial and well-known side effects from our current chemotherapeutic interventions for some myopathies (i.e., corticosteroids).