Contractile properties and magnetic resonance imaging-assessed fat replacement of muscles in myotonia congenita.

BACKGROUND AND PURPOSE: Myotonia congenita (MC) is a muscle channelopathy in which pathogenic variants in a key sarcolemmal chloride channel Gene (CLCN1) cause myotonia. This study used muscle magnetic resonance imaging (MRI) to quantify contractile properties and fat replacement of muscles in a Danish cohort of MC patients. METHODS: Individuals with the Thomsen (dominant) and Becker (recessive) variants of MC were studied. Isometric muscle strength, whole-body MRI, and clinical data were collected. The degree of muscle fat replacement of thigh, calf, and forearm muscles was quantitively calculated on Dixon MRI as fat fractions (FFs). Contractility was evaluated as the muscle strength per contractile muscle cross-sectional area (PT/CCSA). Muscle contractility was compared with clinical data. RESULTS: Intramuscular FF was increased and contractility reduced in calf and in forearm muscles compared with controls (FF = 7.0-14.3% vs. 5.3-9.6%, PT/CCSA = 1.1-4.9 Nm/cm2 vs. 1.9-5.8 Nm/cm2 [p < 0.05]). Becker individuals also showed increased intramuscular FF and reduced contractility of thigh muscles (FF = 11.9% vs. 9.2%, PT/CCSA = 1.9 Nm/cm2 vs. 3.2 Nm/cm2 [p < 0.05]). Individual muscle analysis showed that increased FF was limited to seven of 18 examined muscles (p < 0.05). There was a weak correlation between reduced contractility and severity of symptoms. CONCLUSIONS: Individuals with MC have increased fat replacement and reduced contractile properties of muscles. Nonetheless, changes were small and likely did not impact clinically on their myotonic symptoms.

Repeated oral sucrose dosing after the second wind is unnecessary in patients with McArdle disease: Results from a randomized, placebo-controlled, double-blind, cross-over study.

It is well-established that oral sucrose ingested shortly before exercise improves early exercise tolerance in individuals with McArdle disease. This is by supplying blood-borne glucose for muscle metabolism to compensate for the blocked glycogenolysis. The present study investigated if individuals with McArdle disease could benefit further from repeated sucrose ingestion during prolonged exercise. In this double-blind, placebo-controlled, cross-over study, the participants were randomized to ingest either sucrose or placebo first and subsequently the opposite on two separate days. The participants ingested the drink 10 min before and thrice (after 10, 25, and 40 min) during a 60-min submaximal exercise test on a cycle ergometer. The primary outcome was exercise capacity as indicated by heart rate (HR) and perceived exertion (PE) responses to exercise. Secondary outcomes included changes in blood metabolites, insulin and carbohydrate, and fatty acid oxidation rates during exercise. Nine participants with McArdle disease were included in the study. We confirmed improvement of exercise capacity with oral sucrose vs. placebo during early exercise (pre-second wind) indicated by lower peak HR and PE (p < 0.02). We found no further beneficial effect with repeated sucrose versus placebo ingestion during prolonged exercise, as indicated by no difference in HR or PE post-second wind (p > 0.05). Glucose, lactate, insulin, and carbohydrate oxidation rates increased, and fatty acid oxidation decreased with sucrose versus placebo (p ≤ 0.0002). We can conclude that repeated sucrose ingestion is not recommended during prolonged exercise. This finding can prevent excessive caloric intake and reduce the risk of obesity and insulin resistance.

Axial muscle involvement in patients with limb girdle muscular dystrophy type R9.

INTRODUCTION/AIMS: Limb girdle muscular dystrophy type R9 (LGMDR9) is characterized by progressive weakness of the shoulder and hip girdles. Involvement of proximal extremity muscles is well-described whereas information about axial muscle involvement is lacking. It is important to recognize the involvement of axial muscles to understand functional challenges for the patients. The aim of this study was to investigate the involvement of axial and leg muscles in patients with LGMDR9. METHODS: This observational, cross-sectional study investigated fat replacement of axial and leg muscles in 14 patients with LGMDR9 and 13 matched, healthy controls using quantitative MRI (Dixon technique). We investigated paraspinal muscles at three levels, psoas major at the lumbar level, and leg muscles in the thigh and calf. Trunk strength was assessed with stationary dynamometry and manual muscle tests. RESULTS: Patients with LGMDR9 had significantly increased fat replacement of all investigated axial muscles compared with healthy controls (P < .05). Trunk extension and flexion strength were significantly reduced in patients. Extension strength correlated negatively with mean fat fraction of paraspinal muscles. Fat fractions of all investigated leg muscles were significantly increased versus controls, with the posterior thigh muscles being the most severely affected. DISCUSSION: Patients with LGMDR9 have severe involvement of their axial muscles and correspondingly have reduced trunk extension and flexion strength. Our findings define the axial muscles as some of the most severely involved muscle groups in LGMDR9, which should be considered in the clinical management of the disorder and monitoring of disease progression.

No effect of oral ketone ester supplementation on exercise capacity in patients with McArdle disease and healthy controls: A randomized placebo-controlled cross-over study.

Patients with glycogen storage disease type V (GSDV), also known as McArdle disease, have blocked glycogen breakdown due to myophosphorylase deficiency, leading to exercise intolerance, muscle pain, and risk of muscle damage. Blood-derived ketone bodies (KBs) constitute an alternative energy source that could fuel the muscle independent of glycogenolysis. However, except for long-time fasting or ketogenic dieting, KBs are present in low quantities. This led us to explore the effects of a drink containing exogenously produced KBs in the form of D-ß-hydroxybutyrate esters (KE) on exercise capacity and metabolism in patients with GSDV. Eight GSDV patients and four healthy controls (HC) were included in this placebo-controlled, cross-over study where subjects were randomized to receive a KE drink with 395 mgKE/kg or placebo drink on two separate days 25 min before a submaximal cycle exercise test. The primary outcome was exercise capacity as indicated by heart rate response (HR) to exercise. Secondary outcomes included perceived exertion (PE) and measures of KB, carbohydrate, and fat metabolism during exercise. In GSDV, the KE drink vs. placebo increased plasma KBs and KB oxidation (p ≤ 0.0001) but did not improve exercise capacity as judged from HR (p = 0.120) and PE (p = 0.109). In addition, the KE drink lowered plasma glucose, free fatty acids, and lowered lipolytic rate and glucose rate of appearance compared with placebo. Similar results were found in the HC group. The present study indicates that an increase in KB oxidation by oral KE supplementation does not improve exercise capacity in GSDV possibly because of KB-induced inhibition of lipolysis and liver glucose output. Thus, oral KE supplementation alone cannot be recommended as a treatment option for patients with GSDV.

No effect of resveratrol on fatty acid oxidation or exercise capacity in patients with fatty acid oxidation disorders: A randomized clinical cross-over trial.

The objective was to investigate whether resveratrol (RSV) can improve exercise capacity in patients with fatty acid oxidation (FAO) disorders. The study was a randomized, double-blind, cross-over trial. Nine patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency or carnitine palmitoyl transferase (CPT) II deficiency were randomized to receive either 8 weeks of 1000 mg day-1 RSV or placebo (P) followed by a 4-weeks wash-out period and subsequently 8 weeks of the opposite treatment. Primary outcome measures were heart rate and FAO as measured via stable isotope technique during constant workload exercise. Secondary outcome measures included fat and glucose metabolism; perceived exertion; as well as subjective measures of energy expenditure, fatigue, and daily function. Eight participants completed the trial. Heart rate did not differ at the end of exercise after treatment with RSV vs placebo (P = .063). Rate of oxidation of palmitate at end of exercise was not different with 1.5 ± 0.8 (RSV) vs 1.3 ± 0.6 (P) µmol kg-1  min-1 (P = .109). Secondary outcomes did not change except for increased plasma glycerol and decreased plasma glucose levels at the end of exercise after treatment with RSV vs placebo. A daily dose of 1000 mg resveratrol does not improve exercise capacity or FAO during exercise in patients with CPTII or VLCAD deficiencies.

European Neuromuscular Centre consensus statement on anaesthesia in patients with neuromuscular disorders.

BACKGROUND AND PURPOSE: Patients with neuromuscular conditions are at increased risk of suffering perioperative complications related to anaesthesia. There is currently little specific anaesthetic guidance concerning these patients. Here, we present the European Neuromuscular Centre (ENMC) consensus statement on anaesthesia in patients with neuromuscular disorders as formulated during the 259th ENMC Workshop on Anaesthesia in Neuromuscular Disorders. METHODS: International experts in the field of (paediatric) anaesthesia, neurology, and genetics were invited to participate in the ENMC workshop. A literature search was conducted in PubMed and Embase, the main findings of which were disseminated to the participants and presented during the workshop. Depending on specific expertise, participants presented the existing evidence and their expert opinion concerning anaesthetic management in six specific groups of myopathies and neuromuscular junction disorders. The consensus statement was prepared according to the AGREE II (Appraisal of Guidelines for Research & Evaluation) reporting checklist. The level of evidence has been adapted according to the SIGN (Scottish Intercollegiate Guidelines Network) grading system. The final consensus statement was subjected to a modified Delphi process. RESULTS: A set of general recommendations valid for the anaesthetic management of patients with neuromuscular disorders in general have been formulated. Specific recommendations were formulated for (i) neuromuscular junction disorders, (ii) muscle channelopathies (nondystrophic myotonia and periodic paralysis), (iii) myotonic dystrophy (types 1 and 2), (iv) muscular dystrophies, (v) congenital myopathies and congenital dystrophies, and (vi) mitochondrial and metabolic myopathies. CONCLUSIONS: This ENMC consensus statement summarizes the most important considerations for planning and performing anaesthesia in patients with neuromuscular disorders.

No effect of resveratrol in patients with mitochondrial myopathy: A cross-over randomized controlled trial.

Mitochondrial myopathies (MM) are caused by mutations that typically affect genes involved in oxidative phosphorylation. Main symptoms are exercise intolerance and fatigue. Currently, there is no specific treatment for MM. Resveratrol (RSV) is a nutritional supplement that in preclinical studies has been shown to stimulate mitochondrial function. We hypothesized that RSV could improve exercise capacity in patients with MM. The study design was randomized, double-blind, cross-over and placebo-controlled. Eleven patients with genetically verified MM were randomized to receive either 1000 mg/day RSV or placebo (P) for 8 weeks followed by a 4-week washout and then the opposite treatment. Primary outcomes were changes in heart rate (HR) during submaximal cycling exercise and peak oxygen utilization (VO2 max) during maximal exercise. Secondary outcomes included reduction in perceived exertion, changes in lactate concentrations, self-rated function (SF-36) and fatigue scores (FSS), activities of electron transport chain complexes I and IV in mononuclear cells and mitochondrial biomarkers in muscle tissue among others. There were no significant differences in primary and secondary outcomes between treatments. Mean HR changes were -0.3 ± 4.3 (RSV) vs 1.8 ± 5.0 bpm (P), P = .241. Mean VO2 max changes were 0.7 ± 1.4 (RSV) vs -0.2 ± 2.3 mL/min/kg (P), P = .203. The study provides evidence that 1000 mg RSV daily is ineffective in improving exercise capacity in adults with MM. These findings indicate that previous in vitro studies suggesting a therapeutic potential for RSV in MM, do not translate into clinically meaningful effects in vivo.

New genotype-phenotype correlations in a large European cohort of patients with sarcoglycanopathy.

Sarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. In 2016, several clinicians involved in the diagnosis, management and care of patients with LGMDR3-6 created a European Sarcoglycanopathy Consortium. The aim of the present study was to determine the clinical and genetic spectrum of a large cohort of patients with sarcoglycanopathy in Europe. This was an observational retrospective study. A total of 33 neuromuscular centres from 13 different European countries collected data of the genetically confirmed patients with sarcoglycanopathy followed-up at their centres. Demographic, genetic and clinical data were collected for this study. Data from 439 patients from 13 different countries were collected. Forty-three patients were not included in the analysis because of insufficient clinical information available. A total of 159 patients had a confirmed diagnosis of LGMDR3, 73 of LGMDR4, 157 of LGMDR5 and seven of LGMDR6. Patients with LGMDR3 had a later onset and slower progression of the disease. Cardiac involvement was most frequent in LGMDR4. Sixty per cent of LGMDR3 patients carried one of the following mutations, either in a homozygous or heterozygous state: c.229C>T, c.739G>A or c.850C>T. Similarly, the most common mutations in LMGDR5 patients were c.525delT or c.848G>A. In LGMDR4 patients the most frequent mutation was c.341C>T. We identified onset of symptoms before 10 years of age and residual protein expression lower than 30% as independent risk factors for losing ambulation before 18 years of age, in LGMDR3, LGMDR4 and LGMDR5 patients. This study reports clinical, genetic and protein data of a large European cohort of patients with sarcoglycanopathy. Improving our knowledge about these extremely rare autosomal recessive forms of LGMD was helped by a collaborative effort of neuromuscular centres across Europe. Our study provides important data on the genotype-phenotype correlation that is relevant for the design of natural history studies and upcoming interventional trials in sarcoglycanopathies.

Prolonged fasting-induced hyperketosis, hypoglycaemia and impaired fat oxidation in child and adult patients with spinal muscular atrophy type II.

AIM: This study explored hypoglycaemia and metabolic crises, including hyperketosis, in patients with spinal muscular atrophy (SMA). METHODS: The study comprised four adolescents aged 15-17 and six adults aged 19-37 with SMA type II and eight adult controls aged 21-41, who were recruited by the Rigshospitalet, Denmark, from May 1st to October 30th 2017. We used stable isotope technique and indirect calorimetry to investigate fat and glucose metabolism during a 24-h fast or until hypoglycaemia occurred. RESULTS: All patients with SMA II developed moderate to severe hyperketosis and 60% had symptoms of hypoglycaemia or blood glucose levels below 3 mmol/L. None of the controls developed hyperketosis or hypoglycaemia. Plasma bicarbonate decreased, in line with increased ketone bodies, indicating the start of metabolic acidosis in patients with SMA II. Increased fat production and utilisation were seen in healthy controls during the fasting period, but were absent in patients with SMA II, indicating blunted fat oxidation. CONCLUSION: Low skeletal muscle mass was the best explanation for why patients with SMA II had an increased risk of hypoglycaemia, hyperketosis, metabolic acidosis and disturbed fat and glucose metabolism during fasting. These risks have implications for children facing surgery and those with severe illnesses.

POPDC3 Gene Variants Associate with a New Form of Limb Girdle Muscular Dystrophy.

OBJECTIVE: The Popeye domain containing 3 (POPDC3) gene encodes a membrane protein involved in cyclic adenosine monophosphate (cAMP) signaling. Besides gastric cancer, no disease association has been described. We describe a new muscular dystrophy associated with this gene. METHODS: We screened 1,500 patients with unclassified limb girdle weakness or hyperCKemia for pathogenic POPDC3 variants. Five patients carrying POPDC3 variants were examined by muscle magnetic resonance imaging (MRI), muscle biopsy, and cardiac examination. We performed functional analyses in a zebrafish popdc3 knockdown model and heterologous expression of the mutant proteins in Xenopus laevis oocytes to measure TREK-1 current. RESULTS: We identified homozygous POPDC3 missense variants (p.Leu155His, p.Leu217Phe, and p.Arg261Gln) in 5 patients from 3 ethnically distinct families. Variants affected highly conserved residues in the Popeye (p.Leu155 and p.Leu217) and carboxy-terminal (p.Arg261) domains. The variants were almost absent from control populations. Probands' muscle biopsies were dystrophic, and serum creatine kinase levels were 1,050 to 9,200U/l. Muscle weakness was proximal with adulthood onset in most patients and affected lower earlier than upper limbs. Muscle MRI revealed fat replacement of paraspinal and proximal leg muscles; cardiac investigations were unremarkable. Knockdown of popdc3 in zebrafish, using 2 different splice-site blocking morpholinos, resulted in larvae with tail curling and dystrophic muscle features. All 3 mutants cloned in Xenopus oocytes caused an aberrant modulation of the mechano-gated potassium channel, TREK-1. INTERPRETATION: Our findings point to an important role of POPDC3 for skeletal muscle function and suggest that pathogenic variants in POPDC3 are responsible for a novel type of autosomal recessive limb girdle muscular dystrophy. ANN NEUROL 2019;86:832-843.