Safety and efficacy of tenecteplase in patients with wake-up stroke assessed by non-contrast CT (TWIST): a multicentre, open-label, randomised controlled trial

BACKGROUND

Current evidence supports the use of intravenous thrombolysis with alteplase in patients with wake-up stroke selected with MRI or perfusion imaging and is recommended in clinical guidelines. However, access to advanced imaging techniques is often scarce. We aimed to determine whether thrombolytic treatment with intravenous tenecteplase given within 4·5 h of awakening improves functional outcome in patients with ischaemic wake-up stroke selected using non-contrast CT.

METHODS

TWIST was an investigator-initiated, multicentre, open-label, randomised controlled trial with blinded endpoint assessment, conducted at 77 hospitals in ten countries. We included patients aged 18 years or older with acute ischaemic stroke symptoms upon awakening, limb weakness, a National Institutes of Health Stroke Scale (NIHSS) score of 3 or higher or aphasia, a non-contrast CT examination of the head, and the ability to receive tenecteplase within 4·5 h of awakening. Patients were randomly assigned (1:1) to either a single intravenous bolus of tenecteplase 0·25 mg per kg of bodyweight (maximum 25 mg) or control (no thrombolysis) using a central, web-based, computer-generated randomisation schedule. Trained research personnel, who conducted telephone interviews at 90 days (follow-up), were masked to treatment allocation. Clinical assessments were performed on day 1 (at baseline) and day 7 of hospital admission (or at discharge, whichever occurred first). The primary outcome was functional outcome assessed by the modified Rankin Scale (mRS) at 90 days and analysed using ordinal logistic regression in the intention-to-treat population. This trial is registered with EudraCT (2014-000096-80), ClinicalTrials.gov (NCT03181360), and ISRCTN (10601890).

FINDINGS

From June 12, 2017, to Sept 30, 2021, 578 of the required 600 patients were enrolled (288 randomly assigned to the tenecteplase group and 290 to the control group [intention-to-treat population]). The median age of participants was 73·7 years (IQR 65·9-81·1). 332 (57%) of 578 participants were male and 246 (43%) were female. Treatment with tenecteplase was not associated with better functional outcome, according to mRS score at 90 days (adjusted OR 1·18, 95% CI 0·88-1·58; p=0·27). Mortality at 90 days did not significantly differ between treatment groups (28 [10%] patients in the tenecteplase group and 23 [8%] in the control group; adjusted HR 1·29, 95% CI 0·74-2·26; p=0·37). Symptomatic intracranial haemorrhage occurred in six (2%) patients in the tenecteplase group versus three (1%) in the control group (adjusted OR 2·17, 95% CI 0·53-8·87; p=0·28), whereas any intracranial haemorrhage occurred in 33 (11%) versus 30 (10%) patients (adjusted OR 1·14, 0·67-1·94; p=0·64).

INTERPRETATION

In patients with wake-up stroke selected with non-contrast CT, treatment with tenecteplase was not associated with better functional outcome at 90 days. The number of symptomatic haemorrhages and any intracranial haemorrhages in both treatment groups was similar to findings from previous trials of wake-up stroke patients selected using advanced imaging. Current evidence does not support treatment with tenecteplase in patients selected with non-contrast CT.

FUNDING

Norwegian Clinical Research Therapy in the Specialist Health Services Programme, the Swiss Heart Foundation, the British Heart Foundation, and the Norwegian National Association for Public Health.

Energy metabolism during exercise in patients with β-enolase deficiency (GSDXIII)

AIM

To investigate the in vivo skeletal muscle metabolism in patients with β-enolase deficiency (GSDXIII) during exercise, and the effect of glucose infusion.

METHODS

Three patients with GSDXIII and 10 healthy controls performed a nonischemic handgrip test as well as an incremental cycle ergometer test measuring maximal oxidative consumption (VO2max) and a 1-hour submaximal cycle test at an intensity of 65% to 75% of VO2max. The patients repeated the submaximal exercise after 2 days, where they received a 10% iv-glucose supplementation.

RESULTS

Patients had lower VO2max than healthy controls, and two of three patients had to stop prematurely during the intended 1-hour submaximal exercise test. During nonischemic forearm test, all patients were able to produce lactate in normal amounts. Glucose infusion had no effect on patients' exercise capacity.

CONCLUSIONS

Patients with GSDXIII experience exercise intolerance and episodes of myoglobinuria, even to the point of needing renal dialysis, but still retain an almost normal anaerobic metabolic response to submaximal intensity exercise. In accordance with this, glucose supplementation did not improve exercise capacity. The findings show that GSDXIII, although causing episodic rhabdomyolysis, is one of the mildest metabolic myopathies affecting glycolysis.

Impaired fat oxidation during exercise in multiple acyl-CoA dehydrogenase deficiency

We investigated the in vivo skeletal muscle metabolism in patients with multiple acyl-CoA dehydrogenase deficiency (MADD) during exercise, and the effect of a glucose infusion. Two adults with MADD on riboflavin and l-carnitine treatment and 10 healthy controls performed an incremental exercise test measuring maximal oxidative capacity (VO2max) and a submaximal exercise test (≤1 hour) on a cycle ergometer. During submaximal exercise, we studied fat and carbohydrate oxidation, using stable isotope tracer methodology and indirect calorimetry. On another day, the patients repeated the submaximal exercise receiving a 10% glucose infusion. The patients had a lower VO2max than controls and stopped the submaximal exercise test at 51 and 58 minutes due to muscle pain and exhaustion. The exercise-induced increase in total fatty acid oxidation was blunted in the patients (7.1 and 1.1 vs 12 ± 4 μmol × kg-1 × min-1 in the healthy controls), but total carbohydrate oxidation was higher (67 and 63 vs 25 ± 11 μmol × kg-1 × min-1 in controls). With glucose infusion, muscle pain decreased and average heart rate during exercise dropped in both patients from 124 to 119 bpm and 138 to 119 bpm. We demonstrate that exercise intolerance in MADD-patients relates to an inability to increase fat oxidation appropriately during exercise, which is compensated partially by an increase in carbohydrate metabolism.

L-Carnitine Improves Skeletal Muscle Fat Oxidation in Primary Carnitine Deficiency

CONTEXT

Primary carnitine deficiency (PCD) is an inborn error of fatty acid metabolism. Patients with PCD are risk for sudden heart failure upon fasting or illness if they are not treated with daily l-carnitine.

OBJECTIVE

To investigate energy metabolism during exercise in patients with PCD with and without l-carnitine treatment.

DESIGN

Interventional study.

SETTING

Hospital exercise laboratories and department of cardiology.

PARTICIPANTS

Eight adults with PCD who were homozygous for the c.95A>G (p.N32S) mutation and 10 healthy age- and sex-matched controls.

INTERVENTION

Four-day pause in l-carnitine treatment.

MAIN OUTCOME MEASURES

Total fatty acid and palmitate oxidation rates during 1-hour submaximal cycle ergometer exercise assessed with stable isotope method (U13C-palmitate and 2H2-d-glucose) and indirect calorimetry with and without l-carnitine.

RESULTS

Total fatty acid oxidation rate was higher in patients with l-carnitine treatment during exercise than without treatment [12.3 (SD, 3.7) vs 8.5 (SD, 4.6) µmol × kg-1 × min-1; P = 0.008]. However, the fatty acid oxidation rate was still lower in patients treated with l-carnitine than in the healthy controls [29.5 (SD, 10.1) µmol × kg-1 × min-1; P < 0.001] and in the l-carnitine group without treatment it was less than one third of that in the healthy controls (P < 0.001). In line with this, the palmitate oxidation rates during exercise were lower in the no-treatment period [144 (SD, 66) µmol × kg-1 × min-1] than during treatment [204 (SD, 84) µmol × kg-1 × min-1; P = 0.004) .

CONCLUSIONS

The results indicate that patients with PCD have limited fat oxidation during exercise. l-Carnitine treatment in asymptomatic patients with PCD may not only prevent cardiac complications but also boost skeletal muscle fat metabolism during exercise.

Screening for late-onset Pompe disease in western Denmark

OBJECTIVE

Late-onset Pompe disease (LOPD) is a rare autosomal recessively inherited metabolic myopathy caused by reduced activity of the lysosomal enzyme alpha-glucosidase. In a previous screening study at two large neuromuscular university clinics in Denmark, three patients with LOPD were identified out of 103 patients screened. No systematic screening has been performed at the other neurological departments in the western part of Denmark. Thus, patients with a diagnosis of unspecified myopathy were screened for LOPD.

MATERIALS AND METHODS

At seven neurological departments in the western part of Denmark, medical records were evaluated for all patients registered with myopathy diagnosis codes (ICD 10 codes: G 71.0-71.9 and G 72.0-72.9) during the period January 1, 2002, to December 31, 2012. If no specific diagnosis has been reached, patients were invited for screening. Dried blood spot (DBS) test was used to analyze the activity of the enzyme alpha-glucosidase.

RESULT

A total of 654 patients were identified. From the medical records, information was obtained concerning symptoms, family history, electromyography, muscle biopsy results and creatine kinase levels. Eighty-seven patients (13.3%) (males 61%) at a mean age of 53.3 years (SD 16.5) fulfilled the criteria for screening. A DBS test was performed in 47 (54%) patients. In all patients, the enzyme activity was within reference values.

CONCLUSION

None of the screened patients had a reduced activity of the enzyme alpha-glucosidase. Although the cohort studied was small, our findings do not suggest that LOPD is underdiagnosed in patients with unspecified myopathy in western Denmark.

Impaired glycogen breakdown and synthesis in phosphoglucomutase 1 deficiency

OBJECTIVE

We investigated metabolism and physiological responses to exercise in an 18-year-old woman with multiple congenital abnormalities and exertional muscle fatigue, tightness, and rhabdomyolysis.

METHODS

We studied biochemistry in muscle and fibroblasts, performed mutation analysis, assessed physiological responses to forearm and cycle-ergometer exercise combined with stable-isotope techniques and indirect calorimetry, and evaluated the effect of IV glucose infusion and oral sucrose ingestion on the exercise response.

RESULTS

Phosphoglucomutase type 1 (PGM1) activity in muscle and fibroblasts was severely deficient and PGM1 in muscle was undetectable by Western blot. The patient was compound heterozygous for missense (R422W) and nonsense (Q530X) mutations in PGM1. Forearm exercise elicited no increase in lactate, but an exaggerated increase in ammonia, and provoked a forearm contracture. Comparable to patients with McArdle disease, the patient developed a 'second wind' with a spontaneous fall in exercise heart rate and perceived exertion. Like in McArdle disease, this was attributable to an increase in muscle oxidative capacity. Carbohydrate oxidation was blocked during exercise, and the patient had exaggerated oxidation of fat to fuel exercise. Exercise heart rate and perceived exertion were lower after IV glucose and oral sucrose. Muscle glycogen level was low normal.

CONCLUSIONS

The second wind phenomenon has been considered to be pathognomonic for McArdle disease, but we demonstrate that it can also be present in PGM1 deficiency. We show that severe loss of PGM1 activity causes blocked muscle glycogenolysis that mimics McArdle disease, but may also limit glycogen synthesis, which broadens the phenotypic spectrum of this disorder.

Skeletal muscle metabolism during prolonged exercise in Pompe disease

OBJECTIVE

Pompe disease (glycogenosis type II) is caused by lysosomal alpha-glucosidase deficiency, which leads to a block in intra-lysosomal glycogen breakdown. In spite of enzyme replacement therapy, Pompe disease continues to be a progressive metabolic myopathy. Considering the health benefits of exercise, it is important in Pompe disease to acquire more information about muscle substrate use during exercise.

METHODS

Seven adults with Pompe disease were matched to a healthy control group (1:1). We determined (1) peak oxidative capacity (VO_2peak) and (2) carbohydrate and fatty acid metabolism during submaximal exercise (33 W) for 1 h, using cycle-ergometer exercise, indirect calorimetry and stable isotopes.

RESULTS

In the patients, VO_2peak was less than half of average control values; mean difference -1659 mL/min (CI: -2450 to -867, P = 0.001). However, the respiratory exchange ratio increased to >1.0 and lactate levels rose 5-fold in the patients, indicating significant glycolytic flux. In line with this, during submaximal exercise, the rates of oxidation (ROX) of carbohydrates and palmitate were similar between patients and controls (mean difference 0.226 g/min (CI: 0.611 to -0.078, P = 0.318) and mean difference 0.016 µmol/kg/min (CI: 1.287 to -1.255, P = 0.710), respectively).

CONCLUSION

Reflecting muscle weakness and wasting, Pompe disease is associated with markedly reduced maximal exercise capacity. However, glycogenolysis is not impaired in exercise. Unlike in other metabolic myopathies, skeletal muscle substrate use during exercise is normal in Pompe disease rendering exercise less complicated for e.g. medical or recreational purposes.

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.

Training improves oxidative capacity, but not function, in spinal muscular atrophy type III

INTRODUCTION

In this study we investigated the effect of 12 weeks of cycle ergometer training in patients with spinal muscular atrophy type III (SMA III), a hereditary motor neuron disease with progressive muscle weakness and atrophy.

METHODS

Six SMA III patients and 9 healthy subjects completed a 12-week training program, performing 42 30-minute sessions exercising at 65-70% of maximal oxygen uptake (VO2max ). VO2max , muscle strength, functional tests, and self-reported activities of daily living were assessed before and after the training.

RESULTS

Training induced a 27 ± 3% increase in VO2max (17 ± 2 to 21 ± 2 ml/kg/min, P < 0.001) in patients. However, fatigue was a major complaint and caused 1 patient to drop out, increased the need for sleep in 3 patients, and led to training modifications in 2 patients.

CONCLUSIONS

Cycle exercise improves VO2max in SMA III without causing muscle damage, but it also induces significant fatigue. This warrants study into alternative training methods to improve exercise capacity in SMA III patients.

Exercise in muscle glycogen storage diseases

Glycogen storage diseases (GSD) are inborn errors of glycogen or glucose metabolism. In the GSDs that affect muscle, the consequence of a block in skeletal muscle glycogen breakdown or glucose use, is an impairment of muscular performance and exercise intolerance, owing to 1) an increase in glycogen storage that disrupts contractile function and/or 2) a reduced substrate turnover below the block, which inhibits skeletal muscle ATP production. Immobility is associated with metabolic alterations in muscle leading to an increased dependence on glycogen use and a reduced capacity for fatty acid oxidation. Such changes may be detrimental for persons with GSD from a metabolic perspective. However, exercise may alter skeletal muscle substrate metabolism in ways that are beneficial for patients with GSD, such as improving exercise tolerance and increasing fatty acid oxidation. In addition, a regular exercise program has the potential to improve general health and fitness and improve quality of life, if executed properly. In this review, we describe skeletal muscle substrate use during exercise in GSDs, and how blocks in metabolic pathways affect exercise tolerance in GSDs. We review the studies that have examined the effect of regular exercise training in different types of GSD. Finally, we consider how oral substrate supplementation can improve exercise tolerance and we discuss the precautions that apply to persons with GSD that engage in exercise.

Skeletal muscle metabolism is impaired during exercise in glycogen storage disease type III

OBJECTIVE

Glycogen storage disease type IIIa (GSDIIIa) is classically regarded as a glycogenosis with fixed weakness, but we hypothesized that exercise intolerance in GSDIIIa is related to muscle energy failure and that oral fructose ingestion could improve exercise tolerance in this metabolic myopathy.

METHODS

We challenged metabolism with cycle-ergometer exercise and measured substrate turnover and oxidation rates using stable isotope methodology and indirect calorimetry in 3 patients and 6 age-matched controls on 1 day, and examined the effect of fructose ingestion on exercise tolerance in the patients on another day.

RESULTS

Total fatty acid oxidation rates during exercise were higher in patients than controls, 32.1 (SE 1.2) vs 20.7 (SE 0.5; range 15.8-29.3) μmol/kg/min (p = 0.048), and oxidation of carbohydrates was lower in patients, 1.0 (SE 5.4) vs 38.4 (SE 8.0; range 23.0-77.1) μmol/kg/min (p = 0.024). Fructose ingestion improved exercise tolerance in the patients.

CONCLUSION

Similar to patients with McArdle disease, in whom muscle glycogenolysis is also impaired, GSDIIIa is associated with a reduced skeletal muscle oxidation of carbohydrates and a compensatory increase in fatty acid oxidation, and fructose ingestion improves exercise tolerance. Our results indicate that GSDIIIa should not only be viewed as a glycogenosis with fixed skeletal muscle weakness, but should also be considered among the glycogenoses presenting with exercise-related dynamic symptoms caused by muscular energy deficiency.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that ingestion of fructose improves exercise tolerance in patients with GSDIIIa.

Protein-carbohydrate supplements improve muscle protein balance in muscular dystrophy patients after endurance exercise: a placebo-controlled crossover study

In healthy individuals, postexercise protein supplementation increases muscle protein anabolism. In patients with muscular dystrophies, aerobic exercise improves muscle function, but the effect of exercise on muscle protein balance is unknown. Therefore, we investigated 1) muscle protein balance before, during, and after exercise and 2) the effect of postexercise protein-carbohydrate supplementation on muscle protein balance in patients with muscular dystrophies. In 17 patients [7 women and 10 men, aged 33 ± 11 yr (18-52), body mass index: 22 ± 3 kg/m(2) (16-26)] and 8 healthy matched controls [3 women and 5 men, age 33 ± 13 years (19-54), body mass index: 23 ± 3 kg/m(2) (19-27)], muscle protein synthesis, breakdown, and fractional synthesis rates (FSR) were measured across the leg using tracer dilution methodology on two occasions, with and without oral postexercise protein-carbohydrate supplementation. In patients, muscle protein breakdown increased in the recovery period (11 ± 1 μmol phenylalanine/min) vs. rest (8 ± 1 μmol phenylalanine/min, P = 0.02), enhancing net muscle protein loss. In contrast, postexercise protein-carbohydrate supplementation reduced protein breakdown, abolished net muscle protein loss, and increased the muscle FSR in patients (0.04 to 0.06%/h; P = 0.03). In conclusion, postexercise protein-carbohydrate supplementation reduces skeletal mixed-muscle protein breakdown, enhances FSR, resulting in a reduced net muscle loss in patients with muscular dystrophies. The findings suggest that postexercise protein-carbohydrate supplementation could be an important add-on to exercise training therapy in muscular dystrophies, and long-term studies of postexercise protein-carbohydrate supplementation are warranted in these conditions.

Bezafibrate in skeletal muscle fatty acid oxidation disorders: a randomized clinical trial

OBJECTIVE

To assess whether bezafibrate increases fatty acid oxidation (FAO) and lowers heart rate (HR) during exercise in patients with carnitine palmitoyltransferase (CPT) II and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies.

METHODS

This was a 3-month, randomized, double-blind, crossover study of bezafibrate in patients with CPT II (n = 5) and VLCAD (n = 5) deficiencies. Primary outcome measures were changes in FAO, measured with stable-isotope methodology and indirect calorimetry, and changes in HR during exercise.

RESULTS

Bezafibrate lowered low-density lipoprotein, triglyceride, and free fatty acid concentrations; however, there were no changes in palmitate oxidation, FAO, or HR during exercise.

CONCLUSION

Bezafibrate does not improve clinical symptoms or FAO during exercise in patients with CPT II and VLCAD deficiencies. These findings indicate that previous in vitro studies suggesting a therapeutic potential for fibrates in disorders of FAO do not translate into clinically meaningful effects in vivo.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that bezafibrate 200 mg 3 times daily is ineffective in improving changes in FAO and HR during exercise in adults with CPT II and VLCAD deficiencies.

Late-onset Pompe disease is prevalent in unclassified limb-girdle muscular dystrophies

OBJECTIVE

Late-onset Pompe disease is a rare, but potentially treatable metabolic myopathy, and therefore should not be overlooked. However, it is not unusual that patients go undiagnosed for many years. We hypothesized that patients with late-onset Pompe disease may have been overlooked in a population of patients with unclassified neuromuscular disease.

METHODS

We used DBS (dried blood spots) to screen for Pompe disease in the two largest neuromuscular clinics and one of the main respiratory centers in Denmark. We selected patients with unclassified LGDM (limb-girdle muscular dystrophy), idiopathic elevation of creatine kinase, unexplained myopathy on muscle biopsy, unexplained restrictive respiratory insufficiency or unspecified myopathy for screening.

RESULTS

177 patients were found eligible for inclusion, and 103 (58.2%) patients accepted screening. Three patients with Pompe disease were identified with DBS, and subsequent genetic testing revealed known pathogenic mutations in the GAA gene. All three patients were found among 38 patients with unclassified LGMD (8%).

CONCLUSION

Our findings indicate that a DBS should be considered early in the diagnostic work-up of patients with an LGMD phenotype, to rule out Pompe disease. Retrospectively, all 3 patients presented with "red flags" more compatible with Pompe disease than LGMD, including; 1) mild non-dystrophic, myopathic features on muscle biopsy, 2) creatine kinase levels below 1000, and 3) disproportionate axial and respiratory muscle involvement in comparison with limb muscle involvement.

Fat and carbohydrate metabolism during exercise in phosphoglucomutase type 1 deficiency

CONTEXT

Phosphoglucomutase type 1 (PGM1) deficiency is a rare metabolic myopathy in which symptoms are provoked by exercise.

OBJECTIVE

Because the metabolic block is proximal to the entry of glucose into the glycolytic pathway, we hypothesized that iv glucose could improve the exercise intolerance experienced by the patient.

DESIGN

This was an experimental intervention study.

SETTING

The study was conducted in an exercise laboratory.

SUBJECTS

Subjects were a 37-year-old man with genetically and biochemically verified PGM1 deficiency and 6 healthy subjects.

INTERVENTIONS

Cycle ergometer, peak and submaximal exercise (70% of peak oxygen consumption), and exercise with an iv glucose infusion tests were performed.

MAIN OUTCOME MEASURES

Peak work capacity and substrate metabolism during submaximal exercise with and without an iv glucose infusion were measured.

RESULTS

Peak work capacity in the patient was normal, as were increases in plasma lactate during peak and submaximal exercise. However, the heart rate decreased 11 beats minute⁻¹, the peak work rate increased 12.5%, and exercise was rated as being easier with glucose infusion in the patient. These results were in contrast to those in the control group, in whom no improvements occurred. In addition, the patient tended to become hypoglycemic during submaximal exercise.

CONCLUSIONS

This report characterizes PGM1 deficiency as a mild metabolic myopathy that has dynamic exercise-related symptoms in common with McArdle disease but no second wind phenomenon, thus suggesting that the condition clinically resembles other partial enzymatic defects of glycolysis. However, with glucose infusion, the heart rate decreased 11 beats min⁻¹, the peak work rate increased 12.5%, and exercise was considered easier by the patient.

Exercise intolerance in Glycogen Storage Disease Type III: weakness or energy deficiency?

Myopathic symptoms in Glycogen Storage Disease Type IIIa (GSD IIIa) are generally ascribed to the muscle wasting that these patients suffer in adult life, but an inability to debranch glycogen likely also has an impact on muscle energy metabolism. We hypothesized that patients with GSD IIIa can experience exercise intolerance due to insufficient carbohydrate oxidation in skeletal muscle. Six patients aged 17-36-years were studied. We determined VO 2peak (peak oxygen consumption), the response to forearm exercise, and the metabolic and cardiovascular responses to cycle exercise at 70% of VO 2peak with either a saline or a glucose infusion. VO 2peak was below normal. Glucose improved the work capacity by lowering the heart rate, and increasing the peak work rate by 30% (108 W with glucose vs. 83 W with placebo, p=0.018). The block in muscle glycogenolytic capacity, combined with the liver involvement caused exercise intolerance with dynamic skeletal muscle symptoms (excessive fatigue and muscle pain), and hypoglycemia in 4 subjects. In this study we combined anaerobic and aerobic exercise to systematically study skeletal muscle metabolism and exercise tolerance in patients with GSD IIIa. Exercise capacity was significantly reduced, and our results indicate that this was due to a block in muscle glycogenolytic capacity. Our findings suggest that the general classification of GSD III as a glycogenosis characterized by fixed symptoms related to muscle wasting should be modified to include dynamic exercise-related symptoms of muscle fatigue. A proportion of the skeletal muscle symptoms in GSD IIIa, i.e. weakness and fatigue, may be related to insufficient energy production in muscle.

Patients with medium-chain acyl-coenzyme a dehydrogenase deficiency have impaired oxidation of fat during exercise but no effect of L-carnitine supplementation

BACKGROUND

It is not clear to what extent skeletal muscle is affected in patients with medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD). l-Carnitine is commonly used as a supplement in patients with MCADD, although its beneficial effect has not been verified.

DESIGN

We investigated (1) fuel utilization during prolonged low-intensity exercise in patients with MCADD and (2) the influence of 4 weeks of oral l-carnitine supplementation on fuel utilization during exercise.

METHODS

Four asymptomatic patients with MCADD and 11 untrained, healthy, age- and sex-matched control subjects were included. The subjects performed a 1-hour cycling test at a constant workload corresponding to 55% of Vo2max, while fat and carbohydrate metabolism was assessed, using the stable isotope technique and indirect calorimetry. The patients ingested 100 mg/kg/d of l-carnitine for 4 weeks, after which the cycling tests were repeated.

RESULTS

At rest, palmitate oxidation and total fatty acid oxidation (FAO) rates were similar in patients and healthy control subjects. During constant workload cycling, palmitate oxidation and FAO rates increased in both groups, but increased 2 times as much in healthy control subjects as in patients (P = .007). Palmitate oxidation and FAO rates were unchanged by the l-carnitine supplementation.

CONCLUSION

Our results indicate that patients with MCADD have an impaired ability to increase FAO during exercise but less so than that observed in patients with a number of other disorders of fat oxidation, which explains the milder skeletal muscle phenotype in MCADD. The use of carnitine supplementation in MCADD cannot be supported by the present findings.

Muscle phenotype in patients with myotonic dystrophy type 1

INTRODUCTION

The pathogenesis of muscle involvement in patients with myotonic dystrophy type 1 (DM1) is not well understood. In this study, we characterized the muscle phenotype in patients with confirmed DM1.

METHODS

In 38 patients, muscle strength was tested by hand-held dynamometry. Myotonia was evaluated by a handgrip test and by analyzing the decrement of the compound muscle action potential. Muscle biopsies were assessed for morphological changes and Na(+)-K(+) pump content.

RESULTS

Muscle strength correlated with a decline in Na(+)-K(+) pump content (r = 0.60, P < 0.001) and with CTG expansion. CTG expansion did not correlate with severity of myotonia, proximal histopathological changes, or Na(+)-K(+) pump content. Histopathologically, we found few centrally placed nuclei (range 0.2-6.9%).

CONCLUSIONS

The main findings of this study are that muscle weakness correlated inversely with CTG expansion and that central nuclei are not a prominent feature of proximal muscles in DM1.

Fat and carbohydrate metabolism during exercise in late-onset Pompe disease

Pompe disease is caused by absence of the lysosomal enzyme acid alpha-glucosidase. It is generally assumed that intra-lysosomal hydrolysis of glycogen does not contribute to skeletal muscle energy production during exercise. However, this hypothesis has never been tested in vivo during exercise. We examined the metabolic response to exercise in patients with late-onset Pompe disease, in order to determine if a defect in energy metabolism may play a role in the pathogenesis of Pompe disease. We studied six adult patients with Pompe disease and 10 healthy subjects. The participants underwent ischemic forearm exercise testing, and peak work capacity was determined. Fat and carbohydrate metabolism during cycle exercise was examined with a combination of indirect calorimetry and stable isotope methodology. Finally, the effects of an IV glucose infusion on heart rate, ratings of perceived exertion, and work capacity during exercise were determined. We found that peak oxidative capacity was reduced in the patients to 17.6 vs. 38.8 ml kg(-1) min(-1) in healthy subjects (p = 0.002). There were no differences in the rate of appearance and rate of oxidation of palmitate, or total fat and carbohydrate oxidation, between the patients and the healthy subjects. None of the subjects improved exercise tolerance by IV glucose infusion. In conclusion, peak oxidative capacity is reduced in Pompe disease. However, skeletal muscle fat and carbohydrate use during exercise was normal. The results indicate that a reduced exercise capacity is caused by muscle weakness and wasting, rather than by an impaired skeletal muscle glycogenolytic capacity. Thus, it appears that acid alpha-glucosidase does not play a significant role in the production of energy in skeletal muscle during exercise.

Muscle phosphorylase kinase deficiency: a neutral metabolic variant or a disease?

OBJECTIVE

To examine metabolism during exercise in 2 patients with muscle phosphorylase kinase (PHK) deficiency and to further define the phenotype of this rare glycogen storage disease (GSD).

METHODS

Patient 1 (39 years old) had mild exercise-induced forearm pain, and EMG showed a myopathic pattern. Patient 2 (69 years old) had raised levels of creatine kinase (CK) for more than 6 months after statin treatment. Both patients had increased glycogen levels in muscle and PHK activity <11% of normal. Two novel pathogenic nonsense mutations were found in the PHKA1 gene. The metabolic response to anaerobic forearm exercise and aerobic cycle exercise was studied in the patients and 5 healthy subjects.

RESULTS

Ischemic exercise showed a normal 5-fold increase in plasma lactate (peak 5.7 and 6.9 mmol/L) but an exaggerated 5-fold increase in ammonia (peak 197 and 171 μmol/L; control peak range 60-113 μmol/L). An incremental exercise test to exhaustion revealed a blunted lactate response (5.4 and 4.8 mmol/L) vs that for control subjects (9.6 mmol/L; range 7.1-14.3 mmol/L). Fat and carbohydrate oxidation rates at 70% of peak oxygen consumption were normal. None of the patients developed a second wind phenomenon or improved their work capacity with an IV glucose infusion.

CONCLUSION

Our findings demonstrate that muscle PHK deficiency may present as an almost asymptomatic condition, despite a mild impairment of muscle glycogenolysis, raised CK levels, and glycogen accumulation in muscle. The relative preservation of glycogenolysis is probably explained by an alternative activation of myophosphorylase by AMP and P(i) at high exercise intensities.

Effect of aerobic training in patients with spinal and bulbar muscular atrophy (Kennedy disease)

OBJECTIVE

We examined the effect of aerobic exercise in patients with spinal and bulbar muscular atrophy (SBMA). SBMA is caused by a defect androgen receptor. This defect causes motor neuron death, but considering the important function of androgens in muscle, it is possible that muscle damage in SBMA also occurs independently of motor neuron damage.

METHODS

Eight patients with SBMA engaged in regular cycling exercise for 12 weeks. Maximum oxygen uptake (Vo(2max)), maximal work capacity (W(max)), muscle morphology, citrate synthase (CS) activity, body composition, EMG, static strength measurements, lung function, plasma proteins, and hormones were evaluated before and after training. Evaluation of improvements in activities of daily living (ADL) was conducted after training.

RESULTS

W(max) increased by 18%, and CS activity increased by 35%. There was no significant change in Vo(2max) or any of the other variables examined before and after training, and the patients with SBMA did not feel improvements in ADL.

CONCLUSIONS

Frequent, moderate-intensity aerobic conditioning is of little beneficial effect in patients with spinal and bulbar muscular atrophy (SBMA). High levels of plasma creatine kinase and muscle regeneration indicate a primary myopathic affection, which, in parallel with the motor neuron deficiency, may attenuate the response to exercise training in patients with SBMA.