Mette Cathrine Ørngreen

Aerobic training improves exercise performance in facioscapulohumeral muscular dystrophy

Exercise programs have been shown to increase strength and endurance in patients with myopathic disorders. The authors investigated the effect of aerobic training in patients with facioscapulohumeral dystrophy (FSHD). Twelve weeks of low-intense aerobic exercise improved maximal oxygen uptake and workload with no signs of muscle damage. The authors conclude that aerobic training is a safe method to increase exercise performance in patients with FSHD.

Aerobic training in patients with myotonic dystrophy type 1

The effect of 12 weeks of aerobic training on a cycle ergometer was studied in 12 patients with myotonic dystrophy. Efficacy was evaluated by cycle testing and muscle morphology before and after training. Patients increased their maximal oxygen uptake by 14%, the maximal workload by 11%, muscle fiber diameter increased significantly, and creatine kinase did not increase with training. The study indicates that aerobic training is safe and can improve fitness effectively in patients with myotonic dystrophy. Ann Neurol 2005;57:754–757

Muscle glycogenosis due to phosphoglucomutase 1 deficiency.

To the Editor: Muscle glycogen storage diseases are rare inborn diseases caused by errors of metabolism associated with either dynamic, exercise-related symptoms or permanent muscle weakness. The m...

Fuel utilization in subjects with carnitine palmitoyltransferase 2 gene mutations.

Patients with the myopathic form of carnitine palmitoyltransferase II (CPT II) deficiency typically experience muscle pain, cramps, and myoglobinuria during prolonged exercise. It has been suggested that carriers of CPT2 gene mutations also may have milder clinical symptoms, but fatty acid oxidation (FAO) has never been investigated in vivo in this group. We studied fuel utilization by indirect calorimetry and stable isotope methodology in four patients with CPT II deficiency, three subjects who carried one CPT2 gene mutation, and five healthy control subjects. Cycle exercise at a constant workload of 50% of maximal oxygen uptake capacity was used to facilitate FAO. We found that in vivo oxidation of long‐chain fatty acids was normal at rest but severely impaired during prolonged, low‐intensity exercise in patients with CPT II deficiency, and that two of the single CPT2 gene mutation carriers, who displayed symptoms of CPT II deficiency, had an FAO comparable with the patients. These results indicate that residual CPT II activity is sufficient to maintain long‐chain FAO at rest in CPT II deficiency but not to increase FAO during exercise. The findings also suggest that single CPT2 gene mutations may exert a dominant‐negative effect on the tetrameric CPT II protein. Ann Neurol 2005;57:60–66

Effect of diet on exercise tolerance in carnitine palmitoyltransferase II deficiency

It is generally believed that a diet high in carbohydrate improves exercise tolerance in patients with carnitine palmitoyltransferase II (CPT II) deficiency, but it has never been systematically investigated. The authors investigated the effect of a high- vs low-carbohydrate diet on exercise tolerance in four patients with CPT II, who cycled at a constant workload of 50% of Vo2max. Exercise tolerance, assessed by exercise duration and perceived exertion, improved on the carbohydrate-rich diet.

Fuel utilization in patients with very long-chain acyl-coa dehydrogenase deficiency.

Fuel utilization in two adult patients with the myopathic form of very long‐chain acyl‐CoA dehydrogenase (VLCAD) deficiency and five healthy subjects was investigated with stable isotopes during exercise at 50% of VO2max. The findings indicate that residual VLCAD activity in the patients is sufficient to maintain normal oxidation of fat at rest, but that fat oxidation rate cannot increase above basal levels during exercise. This can cause an energy deficit and intramuscular accumulation of fat intermediates that may induce the exercise‐induced symptoms.

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.

Exercise tolerance in carnitine palmitoyltransferase II deficiency with IV and oral glucose

Background Patients with carnitine palmitoyltransferase II (CPT II) deficiency often experience muscle pain and myoglobinuria during prolonged exercise because of impaired oxidation of long-chain fatty acids. Objective To investigate whether IV or oral glucose can improve exercise tolerance in CPT II deficiency. Methods Five patients with CPT II deficiency and healthy matched volunteers were investigated on a cycle ergometer at a constant workload of 60% of Vo2max. Perceived exertion, heart rate, and venous plasma glucose and insulin levels were monitored. The study was randomized, placebo controlled, single blind, and crossover. Glucose and placebo were administered both orally and IV in patients and IV in healthy subjects. Results In patients with CPT II, exercise duration was prolonged by 28 ± 8% (p = 0.02), and perceived exertion (p = 0.05) and heart rate (p = 0.09) were lowered by glucose infusion. In contrast, IV glucose resulted in higher heart rate during exercise in healthy subjects. Oral glucose and placebo resulted in the same exercise duration, perceived exertion, and heart rate in patients. Plasma glucose and insulin were consistently elevated during exercise by oral and IV glucose vs placebo, but plasma glucose was higher and insulin lower in IV vs oral glucose studies in patients (p = 0.02). Conclusion Exercise tolerance is markedly improved by a glucose infusion in patients with CPT II deficiency, but because of lower glucose availability and higher insulin levels that inhibit muscle glycogenolysis, the patients cannot achieve this effect themselves by oral glucose ingestion.

Fat metabolism during exercise in patients with McArdle disease

Objective: It is known that muscle phosphorylase deficiency restricts carbohydrate utilization, but the implications for muscle fat metabolism have not been studied. We questioned whether patients with McArdle disease can compensate for the blocked muscle glycogen breakdown by enhancing fat oxidation during exercise. Methods: We studied total fat oxidation by indirect calorimetry and palmitate turnover by stable isotope methodology in 11 patients with McArdle disease and 11 healthy controls. Cycle exercise at a constant workload of 50% to 60% of maximal oxygen uptake capacity was used to evaluate fatty acid oxidation (FAO) in the patients. Healthy controls were exercised at the same absolute workload. Results: We found that palmitate oxidation and disposal, total fat oxidation, and plasma levels of palmitate and total free fatty acids (FFAs) were significantly higher, whereas total carbohydrate oxidation was lower, during exercise in patients with McArdle disease vs healthy controls. We found augmented fat oxidation with the onset of a second wind, but further increases in FFA availability, as exercise continued, did not result in further increases in FAO. Conclusion: These results indicate that patients with McArdle disease have exaggerated fat oxidation during prolonged, low-intensity exercise and that increased fat oxidation may be an important mechanism of the spontaneous second wind. The fact that increasing availability of free fatty acids with more prolonged exercise did not increase fatty acid oxidation suggests that blocked glycogenolysis may limit the capacity of fat oxidation to compensate for the energy deficit in McArdle disease. BMI = body mass index; bpm = beats per minute; CHO = carbohydrate oxidation; FAO = fatty acid oxidation; FFA = free fatty acid; Ra = rate of appearance; Rd = rate of disappearance; RER = respiratory exchange rate; Rox = rate of oxidation; TAG = triacylglycerol; TCA = tricarboxylic acid; VO2= oxygen consumption; VO2max = maximal oxygen uptake capacity.

Endocrine function in 97 patients with myotonic dystrophy type 1.

The aim of this study was to investigate the endocrine function and its association to number of CTG repeats in patients with myotonic dystrophy type 1 (DM1). Concentration of various hormones and metabolites in venous blood was used to assess the endocrine function in 97 patients with DM1. Correlation with CTGn expansion size was investigated with the Pearson correlation test. Eighteen percent of the DM1 patients had hyperparathyroidism with increased PTH compared with 0.5% in the background population. Of these, 16% had normocalcemia and 2% had hypercalcemia. An additional 3% had hypercalcemia without elevation of PTH; 7% had abnormal TSH values (2% subnormal and 5% elevated TSH levels); 5% of the patients had type 2 diabetes mellitus; 17% of the male DM1 patients had increased LH and low levels of plasma testosterone indicating absolute androgen insufficiency. Another 21% had increased LH, but normal testosterone levels, indicating relative insufficiency. Numbers of CTG repeats correlated directly with plasma PTH, phosphate, LH, and tended to correlate with plasma testosterone for males. This is the largest study of endocrine dysfunction in a cohort of Caucasian patients with DM1. We found that patients with DM1 have an increased risk of abnormal endocrine function, particularly calcium metabolism disorders. However, the endocrine dysfunction appears not to be of clinical significance in all of the cases. Finally, we found correlations between CTGn expansion size and plasma PTH, phosphate, and testosterone, and neck flexion strength.