Tina D. Jeppesen

Endurance training improves fitness and strength in patients with Becker muscular dystrophy

Studies in a dystrophinopathy model (the mdx mouse) suggest that exercise training may be deleterious for muscle integrity, but exercise has never been studied in detail in humans with defects of dystrophin. We studied the effect of endurance training on conditioning in patients with the dystrophinopathy, Becker muscular dystrophy (BMD). Eleven patients with BMD and seven matched, healthy subjects cycled 50, 30 min sessions at 65% of their maximal oxygen uptake (VO(2max)) over 12 weeks, and six patients continued cycling for 1 year. VO(2max), muscle biopsies, echocardiography, plasma creatine kinase (CK), lower extremity muscle strength and self-reported questionnaires were evaluated before, after 12 weeks and 1 year of training. Endurance training for 12 weeks, improved VO(2max) by 47 +/- 11% and maximal workload by 80 +/- 19% in patients (P < 0.005). This was significantly higher than in healthy subjects (16 +/- 2% and 17 +/- 2%). CK levels did not increase with training, and number of central nuclei, necrotic fibres and fibres expressing neonatal myosin heavy chain did not change in muscle biopsies. Strength in muscles involved in cycle exercise (knee extension, and dorsi- and plantar-flexion) increased significantly by 13-40%. Cardiac pump function, measured by echocardiography, did not change with training. All improvements and safety markers were maintained after 1 year of training. Endurance training is a safe method to increase exercise performance and daily function in patients with BMD. The findings support an active approach to rehabilitation of patients with BMD.

Haemodynamic responses to exercise, ATP infusion and thigh compression in humans: insight into the role of muscle mechanisms on cardiovascular function

The muscle pump and muscle vasodilatory mechanims are thought to play important roles in increasing and maintaining muscle perfusion and cardiac output during exercise, but their actual contributions remain uncertain. To evaluate the role of the skeletal muscle pump and vasodilatation on cardiovascular function during exercise, we determined leg and systemic haemodynamic responses in healthy men during (1) incremental one‐legged knee‐extensor exercise, (2) step‐wise femoral artery ATP infusion at rest, (3) passive exercise (n= 10), (4) femoral vein or artery ATP infusion (n= 6), and (5) cyclic thigh compressions at rest and during passive and voluntary exercise (n= 7). Incremental exercise resulted in progressive increases in leg blood flow (ΔLBF 7.4 ± 0.7 l min−1), cardiac output ( 8.7 ± 0.7 l min−1), mean arterial pressure (ΔMAP 51 ± 5 mmHg), and leg and systemic oxygen delivery and . Arterial ATP infusion resulted in similar increases in , LBF, and systemic and leg oxygen delivery, but central venous pressure and muscle metabolism remained unchanged and MAP was reduced. In contrast, femoral vein ATP infusion did not alter LBF, or MAP. Passive exercise also increased blood flow (ΔLBF 0.7 ± 0.1 l min−1), yet the increase in muscle and systemic perfusion, unrelated to elevations in aerobic metabolism, accounted only for ∼5% of peak exercise hyperaemia. Likewise, thigh compressions alone or in combination with passive exercise increased blood flow (ΔLBF 0.5–0.7 l min−1) without altering , MAP or . These findings suggest that the skeletal muscle pump is not obligatory for sustaining venous return, central venous pressure, stroke volume and or maintaining muscle blood flow during one‐legged exercise in humans. Further, its contribution to muscle and systemic peak exercise hyperaemia appears to be minimal in comparison to the effects of muscle vasodilatation.

Endurance training An effective and safe treatment for patients with LGMD2I

We studied the effect of aerobic training on conditioning in patients with limb-girdle muscular dystrophy type 2I (LGMD2I). Nine patients with LGMD2I cycled fifty 30-minute sessions at 65% of their maximal oxygen uptake over 12 weeks. Training significantly improved work capacity, paralleled by self-reported improvements. Creatine kinase levels did not increase significantly, and muscle morphology was unaffected. Moderate-intensity endurance training is a safe method to increase exercise performance and daily function in patients with LGMD2I.

Oxidative capacity correlates with muscle mutation load in mitochondrial myopathy.

The purpose of this study was to investigate the correlation between the level of mutated mitochondrial DNA in muscle and oxidative capacity in 24 patients with mitochondrial myopathy (MM). Maximal oxygen uptake (VO2max), workload (Wmax), and venous plasma lactate levels were measured during an incremental cycle test to exhaustion in 17 patients with point mutations of mtDNA and in seven with single, large‐scale deletions of mtDNA (chronic progressive external ophthalmoplegia [CPEO]). Results were compared with those in 25 healthy matched subjects. The mutation load in MM patients was 67 ± 5% (range, 29 – 99%). VO2max and Wmax correlated with percentage of heteroplasmy (r > 0.82; p < 0.005) and were lower in patients versus healthy subjects (p < 0.000005). Exercise‐induced peak increases in heart rate, ventilation, and resting plasma lactate levels correlated with muscle mutation load (r > 0.71; p < 0.005). Exercise‐induced increases in plasma lactate correlated with muscle mutation load in CPEO patients (r = 0.95; p < 0.005). Impaired oxidative capacity and ragged red muscle fibers were found in CPEO and 3243A→G patients with mutation loads as low as 45 and 57%, respectively. The study indicates that oxidative capacity correlates directly with skeletal muscle mutation load in MM patients, and that the mutation threshold level for impaired oxidative metabolism in MM patients is lower than found in in vitro studies. Ann Neurol 2003

Tissue specific distribution of the 3243A→G mtDNA mutation

Background: The 3243A→G is a common pathogenic mitochondrial DNA (mtDNA) point mutation causing a variety of different phenotypes. Segregation of this mutation to different tissues during embryonic life and postnatally is still enigmatic. Objective: To investigate the tissue distribution of this mutation. Methods: In 65 individuals from nine families segregating the 3243A→G mutation, the mutation load (% mutated mtDNA) was determined in various tissues. Mutation load was measured in two to four cell types—blood leucocytes, buccal cells, skeletal muscle cells, and urine epithelial cells (UEC)—derived from all three embryogenic germ layers. Results: There was a significant correlation among mutation loads in the four tissues (r = 0.80–0.89, p<0.0001). With blood serving as reference, the mutation load was increased by 16% in buccal mucosa, by 31% in UEC, and by 37% in muscle. There were significant differences between the mitotic tissues blood, buccal mucosa, and UEC (p<0.0001), but no difference between UEC and muscle. Using the present data as a cross sectional investigation, a negative correlation of age with the mutation load was found in blood, while the mutation load in muscle did not change with time; 75% of the children presented with higher mutation loads than their mothers in mitotic tissues but not in the post-mitotic muscle. Conclusions: There appears to be a uniform distribution of mutant mtDNA throughout the three germ layers in embryogenesis. The significant differences between mutation loads of the individual tissue types indicate tissue specific segregation of the 3243A→G mtDNA later in embryogenesis.

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 (Vo2max), maximal work capacity (Wmax), 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: Wmax increased by 18%, and CS activity increased by 35%. There was no significant change in Vo2max 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.

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.

Cycle ergometry is not a sensitive diagnostic test for mitochondrial myopathy

Abstract. Cycle exercise has repeatedly been used to diagnose patients suspected of having mitochondrial myopathy (MM), in whom exercise intolerance and lactic acidosis are common. No standardized test, however, has been established. We evaluated the diagnostic value of incremental and constant workload (20 min at 65 % VO2max) cycle tests for the diagnosis of MM. Plasma lactate and oxidative capacity (VO2 and workload) were measured in 15 well-characterized MM patients during cycling. Findings were compared with those in 10 myotonic dystrophy patients and 18 sedentary, healthy subjects.All MM patients had ragged red or COX-negative fibers on muscle biopsy. VO2max and maximal workload were lower in MM than in control groups (P < 0.02). Resting plasma lactate was higher in MM than in control groups (P < 0.005; sensitivity = 93 %; specificity = 85 %), while exercise-induced increases in plasma lactate were only higher during the constant workload protocol in MM patients vs. control groups (P < 0.05; sensitivity = 27 %; specificity = 86 %). The findings indicate that the diagnostic value of a constant workload protocol is superior to an incremental cycle test, but that the test is less sensitive for MM than simple testing of resting lactate and muscle morphology. Cycle testing of MM patients remains an important research tool, but should not be a standard diagnostic procedure for MM.

Clinical presentation and mutations in Danish patients with Wilson disease.

This study describes the clinical presentation and diagnosis in all Danish patients (49, 41 unrelated) with Wilson disease (WND). On the basis of the number of diagnosed patients from 1990–2008, the prevalence was estimated to be 1:49 500. Among routinely used diagnostic tests, none were consistently indicative of WND, with the exception of the 24-h urine-Cu test, which is always outside the normal range. Mutations were identified in 100% of the screened ATP7B alleles (70 unrelated), including five novel mutations: p.1021K; p.G1158V; p.L1304F; IVS20-2A>G; Ex5_6del. In all, 70% of mutations were found in exons 8, 14, 17, 18, and 20. The most frequent mutation, p.H1069Q, comprised 18%. We propose a new and simple model that correlates genotype and age of onset. By assuming that the milder of two mutations is ‘functionally dominant’ and determines the age of onset, we classified 25/27 mutations as either severe (age of onset <20 years) or moderate (age of onset >20 years), and correctly predicted the age of onset in 37/39 patients. This method should be tested in other Wilson populations.

Late onset of stroke-like episode associated with a 3256C→T point mutation of mitochondrial DNA

Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) are usually associated with the common 3243A-->G mutation of mtDNA. Onset of stroke-like episodes usually occurs before age 30. We report a patient with late onset MELAS harboring a rare 3256C-->T mutation in the tRNA(Leu(UUR)) gene of mtDNA. The patient presented with a stroke-like episode at age 36. MRI showed a stroke-like lesion in the right parietooccipital brain region. Proton MR spectroscopy showed elevated lactate concentrations in the lesion (8.4 mmol/l), and in the mid-occipital region (2.3-3.2 mmol/l) that appeared normal on MRI. Further tests revealed evidence of a severe oxidative defect of muscle metabolism as well.