The investigation and management of metabolic myopathies

Raised CK and acute kidney injury following intense exercise in three patients with a history of exercise intolerance due to homozygous mutations in SLC2A9

Acute rhabdomyolysis (AR) leading to acute kidney injury has many underlying etiologies, however, when the primary trigger is exercise, the most usual underlying cause is either a genetic muscle disorder or unaccustomed intense exercise in a healthy individual. Three adult men presented with a history of exercise intolerance and episodes of acute renal impairment following intense exercise, thought to be due to AR in the case of two, and dehydration in one. The baseline serum CK was mildly raised between attacks in all three patients and acutely raised during attacks in two of the three patients. Following referral to a specialized neuromuscular centre, further investigation identified very low serum urate (<12 umol/L). In all three men, genetic studies confirmed homozygous mutations in SLC2A9, which encodes for facilitated glucose transporter member 9 (GLUT9), a major regulator of urate homeostasis. Hereditary hypouricaemia should be considered in people presenting with acute kidney injury related to intense exercise. Serum urate evaluation is a useful screening test best undertaken after recovery.

CONVENTIONAL APPROACHES TO THE THERAPY OF HEREDITARY MYOPATHIES

The aim of the work was to analyze the available therapeutic options for the conventional therapy of hereditary myopathies.

Materials and methods. When searching for the material for writing a review article, such abstract databases as PubMed and Google Scholar were used. The search was carried out on the publications during the period from 1980 to September 2022. The following words and their combinations were selected as parameters for the literature selection: “myopathy”, “Duchenne”, “myodystrophy”, “metabolic”, “mitochondrial”, “congenital”, “symptoms”, “replacement”, “recombinant”, “corticosteroids”, “vitamins”, “tirasemtiv”, “therapy”, “treatment”, “evidence”, “clinical trials”, “patients”, “dichloracetate”.

Results. Congenital myopathies are a heterogeneous group of pathologies that are caused by atrophy and degeneration of muscle fibers due to mutations in genes. Based on a number of clinical and pathogenetic features, hereditary myopathies are divided into: 1) congenital myopathies; 2) muscular dystrophy; 3) mitochondrial and 4) metabolic myopathies. At the same time, treatment approaches vary significantly depending on the type of myopathy and can be based on 1) substitution of the mutant protein; 2) an increase in its expression; 3) stimulation of the internal compensatory pathways expression; 4) restoration of the compounds balance associated with the mutant protein function (for enzymes); 5) impact on the mitochondrial function (with metabolic and mitochondrial myopathies); 6) reduction of inflammation and fibrosis (with muscular dystrophies); as well as 7) an increase in muscle mass and strength. The current review presents current data on each of the listed approaches, as well as specific pharmacological agents with a description of their action mechanisms.

Conclusion. Currently, the following pharmacological groups are used or undergoing clinical trials for the treatment of various myopathies types: inotropic, anti-inflammatory and antifibrotic drugs, antimyostatin therapy and the drugs that promote translation through stop codons (applicable for nonsense mutations). In addition, metabolic drugs, metabolic enzyme cofactors, mitochondrial biogenesis stimulators, and antioxidants can be used to treat myopathies. Finally, the recombinant drugs alglucosidase and avalglucosidase have been clinically approved for the replacement therapy of metabolic myopathies (Pompe’s disease).

Using gene panels in the diagnosis of neuromuscular disorders: A mini-review

The diagnosis of inherited neuromuscular disorders is challenging due to their genetic and phenotypic variability. Traditionally, neurophysiology and histopathology were primarily used in the initial diagnostic approach to these conditions. Sanger sequencing for molecular diagnosis was less frequently utilized as its application was a time-consuming and cost-intensive process. The advent and accessibility of next-generation sequencing (NGS) has revolutionized the evaluation process of genetically heterogenous neuromuscular disorders. Current NGS diagnostic testing approaches include gene panels, whole exome sequencing (WES), and whole genome sequencing (WGS). Gene panels are often the most widely used, being more accessible due to availability and affordability. In this mini-review, we describe the benefits and risks of clinical genetic testing. We also discuss the utility, benefits, challenges, and limitations of using gene panels in the evaluation of neuromuscular disorders.

A novel HADHA variant associated with an atypical moderate and late-onset LCHAD deficiency

Background

Long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a rare inherited disease caused by pathogenic variants of HADHA gene. Along with signs common to fatty acid oxidation defects (FAOD), specific retina and heart alterations are observed. Because long-chain fatty acid oxidation is selectively affected, supplementations with short/medium-chain fats represent energetic sources bypassing the enzymatic blockade. Here, we report on an atypical presentation of the disease.

Methods

Clinical features were described with medical explorations including ophthalmic and cardiac examination. Biological underlying defects were investigated by measurements of biochemical metabolites and by fluxomic studies of mitochondrial β-oxidation. Whole exome sequencing and molecular validation of variants confirmed the diagnosis.

Results

The patient has developed at nine years an unlabeled maculopathy, and at 28 years, an acute cardiac decompensation without any premise. Blood individual acylcarnitine analysis showed a rise in hydroxylated long-chain fatty acids and fluxomic studies validated enzyme blockade consistent with LCHADD. Genetic analysis revealed the common p.(Glu510Gln) variant in HADHA, in trans with a novel variant c.1108G > A, p.(Gly370Arg) located in the NAD binding domain. Patient pathology was responsive to triheptanoin supplementation.

Conclusion

This atypical LCHADD form report should encourage the early assessment of biochemical and genetic testing as a specific management is recommended (combination with fast avoidance, low fat-high carbohydrate diet, medium-even-chain triglycerides or triheptanoin supplementation).

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Mild hyperpigmented macular dots could be the first and early symptom of moderate LCHAD.

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The novel HADHA c.1108G > A, p.(Gly370Arg) is hypomorphic and associated with moderate LCHAD.

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Atypical and late LCHAD can be deciphered by joint biochemical and genetical investigations.

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Acylcarnitines must be tested in unexplained macular dystrophy and/or dilated cardiomyopathy.

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Supplementation with the triglyceride triheptanoin is effective.

Pain Phenotypes in Rare Musculoskeletal and Neuromuscular Diseases

For patients diagnosed with a rare musculoskeletal or neuromuscular disease, pain may transition from acute to chronic; the latter yielding additional challenges for both patients and care providers. We assessed the present understanding of pain across a set of ten rare, noninfectious, noncancerous disorders; Osteogenesis Imperfecta, Ehlers-Danlos Syndrome, Achondroplasia, Fibrodysplasia Ossificans Progressiva, Fibrous Dysplasia/McCune-Albright Syndrome, Complex Regional Pain Syndrome, Duchenne Muscular Dystrophy, Infantile- and Late-Onset Pompe disease, Charcot-Marie-Tooth Disease, and Amyotrophic Lateral Sclerosis. Through the integration of natural history, cross-sectional, retrospective, clinical trials, & case studies we described pathologic and genetic factors, pain sources, phenotypes, and lastly, existing therapeutic approaches. We highlight that while rare diseases possess distinct core pathologic features, there are a number of shared pain phenotypes and mechanisms that may be prospectively examined and therapeutically targeted in a parallel manner. Finally, we describe clinical and research approaches that may facilitate more accurate diagnosis, monitoring, and treatment of pain as well as elucidation of the evolving nature of pain phenotypes in rare musculoskeletal or neuromuscular illnesses.

Severe rhabdomyolysis in homozygote carnitine palmitoyltransferase II deficiency

Carnitine palmitoyltransferase II (CPT II) deficiency represents an inherited defect in mitochondrial long-chain fatty acid oxidation. Rhabdomyolysis with necrosis of muscle is caused by the destruction of skeletal muscle and leads to systemic, multiorgan complications due to the release of intracellular muscle components. Severe rhabdomyolysis may be triggered by combination of a genetic predisposition, including CPT II deficiency, with additionally acting causes. Generally, patients with CPT II deficiency are rarely clinical recognized and reported. We describe a patient presenting severe rhabdomyolysis due to urosepsis, who, in genetic testing, demonstrated the homozygous CPT II deficiency (c.338C>T, p.Ser113Leu) mutation. The diagnosis of CPT II deficiency helped this patient to put the symptoms into context, and this reduced myopathy and the risk of recurring rhabdomyolysis. We report on this patient to increase awareness of diagnostic and medical management in CPT II deficiency.

Update Review about Metabolic Myopathies

The aim of this review is to summarize and discuss recent findings and new insights in the etiology and phenotype of metabolic myopathies. The review relies on a systematic literature review of recent publications. Metabolic myopathies are a heterogeneous group of disorders characterized by mostly inherited defects of enzymatic pathways involved in muscle cell metabolism. Metabolic myopathies present with either permanent (fixed) or episodic abnormalities, such as weakness, wasting, exercise-intolerance, myalgia, or an increase of muscle breakdown products (creatine-kinase, myoglobin) during exercise. Though limb and respiratory muscles are most frequently affected, facial, extra-ocular, and axial muscles may be occasionally also involved. Age at onset and prognosis vary considerably. There are multiple disease mechanisms and the pathophysiology is complex. Genes most recently related to metabolic myopathy include PGM1, GYG1, RBCK1, VMA21, MTO1, KARS, and ISCA2. The number of metabolic myopathies is steadily increasing. There is limited evidence from the literature that could guide diagnosis and treatment of metabolic myopathies. Treatment is limited to mainly non-invasive or invasive symptomatic measures. In conclusion, the field of metabolic myopathies is evolving with the more widespread availability and application of next generation sequencing technologies worldwide. This will broaden the knowledge about pathophysiology and putative therapeutic strategies for this group of neuromuscular disorders.

Update on diagnostics of metabolic myopathies

PURPOSE OF REVIEW

This review aims to highlight the most relevant clinical and laboratory findings, regarding acute and progressive metabolic myopathies, and to develop an algorithm addressing clinicians to clinical practice.

RECENT FINDINGS

Although diagnosis of metabolic myopathies remains still challenging, the recent identification of new disorders has increased the number of patients requiring specific investigations. Nowadays, a more detailed characterization of the clinical spectrum of metabolic myopathies improved awareness as well as a deeper knowledge on their natural history or multisystem involvement. Diagnostic procedures, as first-line screening tests are necessary for an earlier and more accurate diagnostic work up, not only in infantile cases, but also in adults with suspected metabolic myopathies. New generation diagnostic techniques such as NGS (Next Generation Sequencing) and whole exome/genome sequencing have emerged as innovative tools to extensively evaluate either known genes variants or new candidate genes as possible causes of metabolic myopathies.

SUMMARY

Diagnosis of metabolic myopathies is still challenging for clinicians because of rarity and clinical heterogeneity which is often overlapping with other neuromuscular disorders. Detailed algorithms supported by advanced laboratory investigations may be helpful to timely reach a diagnosis, so allowing an earlier therapeutic decision.

Carnitine Palmitoyltransferase II Deficiency (CPT II) Followed By Rhabdomyolysis and Acute Kidney Injury

BACKGROUND:

Carnitine palmitoyltransferase II deficiency (CPT II) is an autosomal recessive disorder and the most common inherited disorder of mitochondrial long-chain fatty acid oxidation, characterised by attacks of myalgia and myoglobinuria. The most common “classic” myopathic form occurs in young adults and is characterised by recurrent episodes of rhabdomyolysis triggered by prolonged exercise, fasting or febrile illness.

CASE PRESENTATION:

We present a case of a 22-year-old Caucasian male admitted to our hospital with fever, dyspnea, fatigue, myalgia and dark urine (brown-coloured). The symptoms appeared after viral infection followed by fever. Acute kidney injury (AKI) developed as a complication, and there was a need for treatment with hemodialysis. At the clinical presentation, the patient had plasma creatine kinase (pCK) level of 130.383 U/L and plasma myoglobin level over 5000 µg/L. Genetic testing (molecular analysis) confirmed the diagnosis of inherited rhabdomyolysis, a metabolic disorder of carnitine palmitoyltransferase II deficiency. A previous episode with the same symptoms, the patient had four years ago but did not ask for medical treatment. The patient was discontinued from hemodialysis because of the resolution of acute kidney injury. The patient was discharged from the hospital in good condition, with a recommendation about his future lifestyle in order to prevent similar episodes.

CONCLUSION:

Every patient presenting with myalgia, dark urine (brown-coloured), high level of pCK and development of AKI requiring hemodialysis, should be explored for inherited rhabdomyolysis induced by CPT II deficiency.

Recurrent rhabdomyolysis caused by carnitine palmitoyltransferase II deficiency, common but under-recognised: Lessons to be learnt

We discuss two adult siblings who presented with symptoms of myalgia and rhabdomyolysis following exercise with myoglobinuria; genetic testing confirmed carnitine palmitoyltransferase II deficiency and resulted in institution of appropriate crisis management and dietary advice. We explore the phenotypic variability of this commonest fatty oxidation defect that remains under-diagnosed in the adult population and provide clues for early recognition and diagnosis.

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CPT II deficiency should be considered as an important differential diagnosis in individuals presenting with recurrent or even single attacks of muscle weakness.

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If the clinical history includes ‘unexplained’ rhabdomyolysis, clinicians should have a low threshold to perform plasma acylcarnitine analysis as a first line investigation, especially in the context of elevated CK.

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Confirmatory diagnosis is by identification of disease-causing variants in CPT2 through targeted testing.

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It is important that these individuals have specialist dietary advice and annual monitoring.

Neuropathic and Myopathic Pain

The evaluation and management of childhood pain syndromes of neuromuscular origin have distinct challenges, as the patterns of disease presentation and the ability of a child to describe symptoms may differ from that of an adult. Advances in scientific and clinical knowledge are leading to significant progress in the care of affected children. The genetic origins of Fabry disease and the inherited form of erythromelalgia are better understood. The increasing interest in neuroimmunology among pediatric neurologists has led to more sophisticated diagnostic and therapeutic approaches. Treatment protocols for complex regional pain syndrome have become more standardized. In addition, investigations continue into potential new interventions for metabolic muscle diseases such as McArdle disease and carnitine palmitoyl transferase deficiency type II. In the years to come, children with pain of neuromuscular origin will have access to more precise diagnostic tools and novel therapies that would alleviate this particularly distressing category of disease.

Recurrent Muscle Weakness with Rhabdomyolysis, Metabolic Crises, and Cardiac Arrhythmia Due to Bi-allelic TANGO2 Mutations

The underlying genetic etiology of rhabdomyolysis remains elusive in a significant fraction of individuals presenting with recurrent metabolic crises and muscle weakness. Using exome sequencing, we identified bi-allelic mutations in TANGO2 encoding transport and Golgi organization 2 homolog (Drosophila) in 12 subjects with episodic rhabdomyolysis, hypoglycemia, hyperammonemia, and susceptibility to life-threatening cardiac tachyarrhythmias. A recurrent homozygous c.460G>A (p.Gly154Arg) mutation was found in four unrelated individuals of Hispanic/Latino origin, and a homozygous ∼34 kb deletion affecting exons 3-9 was observed in two families of European ancestry. One individual of mixed Hispanic/European descent was found to be compound heterozygous for c.460G>A (p.Gly154Arg) and the deletion of exons 3-9. Additionally, a homozygous exons 4-6 deletion was identified in a consanguineous Middle Eastern Arab family. No homozygotes have been reported for these changes in control databases. Fibroblasts derived from a subject with the recurrent c.460G>A (p.Gly154Arg) mutation showed evidence of increased endoplasmic reticulum stress and a reduction in Golgi volume density in comparison to control. Our results show that the c.460G>A (p.Gly154Arg) mutation and the exons 3-9 heterozygous deletion in TANGO2 are recurrent pathogenic alleles present in the Latino/Hispanic and European populations, respectively, causing considerable morbidity in the homozygotes in these populations.