The diagnostic significance of serum enzymes and electrocardiogram in various muscular dystrophies

Calcium ion in skeletal muscle: its crucial role for muscle function, plasticity, and disease

Mammalian skeletal muscle shows an enormous variability in its functional features such as rate of force production, resistance to fatigue, and energy metabolism, with a wide spectrum from slow aerobic to fast anaerobic physiology. In addition, skeletal muscle exhibits high plasticity that is based on the potential of the muscle fibers to undergo changes of their cytoarchitecture and composition of specific muscle protein isoforms. Adaptive changes of the muscle fibers occur in response to a variety of stimuli such as, e.g., growth and differentition factors, hormones, nerve signals, or exercise. Additionally, the muscle fibers are arranged in compartments that often function as largely independent muscular subunits. All muscle fibers use Ca(2+) as their main regulatory and signaling molecule. Therefore, contractile properties of muscle fibers are dependent on the variable expression of proteins involved in Ca(2+) signaling and handling. Molecular diversity of the main proteins in the Ca(2+) signaling apparatus (the calcium cycle) largely determines the contraction and relaxation properties of a muscle fiber. The Ca(2+) signaling apparatus includes 1) the ryanodine receptor that is the sarcoplasmic reticulum Ca(2+) release channel, 2) the troponin protein complex that mediates the Ca(2+) effect to the myofibrillar structures leading to contraction, 3) the Ca(2+) pump responsible for Ca(2+) reuptake into the sarcoplasmic reticulum, and 4) calsequestrin, the Ca(2+) storage protein in the sarcoplasmic reticulum. In addition, a multitude of Ca(2+)-binding proteins is present in muscle tissue including parvalbumin, calmodulin, S100 proteins, annexins, sorcin, myosin light chains, beta-actinin, calcineurin, and calpain. These Ca(2+)-binding proteins may either exert an important role in Ca(2+)-triggered muscle contraction under certain conditions or modulate other muscle activities such as protein metabolism, differentiation, and growth. Recently, several Ca(2+) signaling and handling molecules have been shown to be altered in muscle diseases. Functional alterations of Ca(2+) handling seem to be responsible for the pathophysiological conditions seen in dystrophinopathies, Brody's disease, and malignant hyperthermia. These also underline the importance of the affected molecules for correct muscle performance.

Myotonic ADR-MDX mutant mice show less severe muscular dystrophy than MDX mice

In Duchenne muscular dystrophy (DMD) and its murine model, the dystrophic mouse (MDX), the skeletal musculature lacks dystrophin. The presumed function of this cytoskeletal protein is to protect the sarcolemma against mechanical stress during muscle activity. To test this hypothesis in vivo, we bred a double mutant mouse that combines two genetic defects: the dystrophin-deficiency of the MDX mouse and the Cl- channel myotonia of the arrested development of righting response (ADR) mouse. We hypothesized that high mechanical muscle activity would aggravate muscular dystrophy in double mutant ADR-MDX mice. On the contrary, ADR-MDX mice showed fewer signs of muscle fiber necrosis and fibrosis than MDX mice at all ages. Plasma creatine kinase levels were slightly increased in ADR-MDX, but significantly lower when compared to MDX mice. Sections of ADR-MDX muscle showed a uniform pattern of oxidative muscle fibers. Similar findings have been obtained in dystrophin-positive ADR mice, they result from a complete fiber-type IIB to IIA transformation in myotonic muscle. Our results suggest that small, oxidative fibers of myotonic mice are less sensitive to dystrophin deficiency. Therefore, ADR-MDX mice develop less severe muscular dystrophy than MDX mice do, although their muscles are continually stressed. The new ADR-MDX double mutant mouse is the first animal model combining both a dystrophinopathy and a channelopathy. The results presented here give new insights into the pathomechanism of muscular dystrophy and may be helpful for the therapeutic management of DMD.

Two successful double-blind trials with coenzyme Q10 (vitamin Q10) on muscular dystrophies and neurogenic atrophies

Coenzyme Q10 (vitamin Q10) is biosynthesized in the human body and is functional in bioenergetics, anti-oxidation reactions, and in growth control, etc. It is indispensable to health and survival. The first double-blind trial was with twelve patients, ranging from 7-69 years of age, having diseases including the Duchenne, Becker, and the limb-girdle dystrophies, myotonic dystrophy. Charcot-Marie-Tooth disease, and the Welander disease. The control coenzyme Q10 (CoQ10) blood level was low and ranged from 0.5-0.84 microgram/ml. They were treated for three months with 100 mg daily of CoQ10 and a matching placebo. The second double-blind trial was similar with fifteen patients having the same categories of disease. Since cardiac disease is established to be associated with these muscle diseases, cardiac function was blindly monitored, and not one mistake was made in assigning CoQ10 and placebo to the patients in both trials. Definitely improved physical performance was recorded. In retrospect, a dosage of 100 mg was too low although effective and safe. Patients suffering from these muscle dystrophies and the like, should be treated with vitamin Q10 indefinitely.

Duchenne's cardiomyopathy in a canine model: electrocardiographic and echocardiographic studies

Thirteen dogs affected with X-linked Duchenne's muscular dystrophy and 11 female carrier dogs were studied by electrocardiography (ECG) and echocardiography. Twelve of the affected dogs were studied as immature animals and followed at 1 to 6 month intervals until they were 7 to 46 months of age. Compared with control dogs, affected dogs had significantly increased (p less than 0.02) Q/R ratios in ECG leads II, III, aVF, CV6LL (V2) and CV6LU (V4). Carrier dogs had significantly increased (p less than 0.02) Q/R ratios in leads V2 and V4. The Q/R ratio increased in three of six dogs followed up from age 6 months to greater than 2 years. The PR intervals were significantly shorter (p less than 0.02) in affected dogs. Ventricular arrhythmias were identified in four of six mature affected dogs. Two-dimensional echocardiography revealed distinctive hyperechoic lesions in 12 of the 13 affected dogs and in 6 of the 11 carrier dogs. Hyperechoic lesions corresponded to calcified myocardium and surrounding dense connective tissue. This study establishes the dog affected with Duchenne's muscular dystrophy as an animal model of Duchenne's cardiomyopathy and demonstrates that the heart in carrier dogs is affected by the dystrophic process.

Serum CK-MB activity in progressive muscular dystrophy: is it of nosologic value?

Serum creatine-kinase (CK) isoenzyme MB was measured in 53 patients affected by different types of myopathies (20 with Duchenne muscular dystrophy (DMD), eight with the Becker form (BMD), ten with the limb-girdle form (LGMD), six with the facioscapulohumeral form (FSH), and nine affected by polymyositis and in 21 normal control subjects). The aim of this study was to compare each group with the control individuals and to assess the nosologic value of CK-MB activity among some clinically similar dystrophies, which may have an important application for genetic counseling. A statistically significant increased CK-MB activity was found only in the Duchenne and Becker patients when compared with control persons (p less than 0.05). When the different groups of patients were compared among themselves, no significant difference was found between DMD and BMD or LGMD and polymyositis. However, a significant difference was found between BMD and LGMD. Based on these data, it is possible, through discriminant analysis, to estimate the relative biochemical probability of an isolated male patient belonging to either group.

Biochemical rationale and the cardiac response of patients with muscle disease to therapy with coenzyme Q10

Cardiac disease is commonly associated with virtually every form of muscular dystrophy and myopathy. A double-blind and open crossover trial on the oral administration of coenzyme Q10 (CoQ10) to 12 patients with progressive muscular dystrophies and neurogenic atrophies was conducted. These diseases included the Duchenne, Becker, and limb-girdle dystrophies, myotonic dystrophy, Charcot-Marie-Tooth disease, and Welander disease. The impaired cardiac function was noninvasively and extensively monitored by impedance cardiography. Solely by significant change or no change in stroke volume and cardiac output, all 8 patients on blind CoQ10 and all 4 on blind placebo were correctly assigned (P less than 0.003). After the limited 3-month trial, improved physical well-being was observed for 4/8 treated patients and for 0/4 placebo patients; of the latter, 3/4 improved on CoQ10; 2/8 patients resigned before crossover; 5/6 on CoQ10 in crossover maintained improved cardiac function; 1/6 crossed over from CoQ10 to placebo relapsed. The rationale of this trial was based on known mitochondrial myopathies, which involve respiratory enzymes, the known presence of CoQ10 in respiration, and prior clinical data on CoQ10 and dystrophy. These results indicate that the impaired myocardial function of such patients with muscular disease may have some association with impaired function of skeletal muscle, both of which may be improved by CoQ10 therapy. The cardiac improvement was definitely positive. The improvement in well-being was subjective, but probably real. Likely, CoQ10 does not alter genetic defects but can benefit the sequelae of mitochondrial impairment from such defects. CoQ10 is the only known substance that offers a safe and improved quality of life for such patients having muscle disease, and it is based on intrinsic bioenergetics.

Benign X-linked muscular dystrophy (Becker type): a kindred with very slow rate of progression

A family with benign X-linked muscular dystrophy (Becker type) has been studied. There was a total of 8 affected males, 7 of whom were alive. The clinical and pathological features are presented. The clinical symptoms started in the 2nd decade for most of the patients. The rate of progression was very slow and 3 patients became confined to a wheelchair in the second half of the 6th decade.

Serum pyruvate-kinase (PK) and creatine-phosphokinase (CPK) in progressive muscular dystrophies

PK and CPK have been determined in the serum from 208 individuals including 70 normal controls (61 adults and 9 children) and 138 patients with a variety of neuromuscular disorders. In adult controls the mean activity (+/- SE) for PK is 1.2 +/- 0.05 mumol/ml/h. In normal children PK activity was about twice as high as in normal adults and decreases with increasing age. In 26 patients with Duchenne dystrophy the range of serum PK was 4.0-150.4 and in 17 individuals with the Becker type, 3.0 to 148.7. All had elevated PK and CPK levels. Eighteen of 20 patients with the facio-scapulo-humeral (FSH) from of muscular dystrophy had increased PK while only 9 had elevated CPK. Regression analyses have shown an inverse correlation between PK levels and age (or degree of disability in DMD). Kinetic and electrophoretic studies indicate that the PK isozyme found in the serum from affected patients and from heterozygotes for the DMD gene is mainly the M1 type PK, which is the only PK isozyme found in skeletal muscle and brain and the major component from myocardium.

Clinical studies in benign (Becker type) X-linked muscular dystrophy

Ten extensive families with benign (Becker type) X-linked muscular dystrophy have been studied, in which there was a total of 67 affected males. Reliable information was available on 41 of these males, 29 of whom were alive at the time of the study. The disorder was characterised by a predominantly proximal myopathy, associated with pseudohypertrophy of the calf muscles, particularly in the early stages of the disease. The early development of contractures was not a feature of the disease in these families and cardiac involvement, when present, was a late manifestation. The clinical findings in these patients are discussed in detail and compared with those in a large unselected group of patients with Duchenne muscular dystrophy. The results indicate that the best criterion for distinguishing between these two disorders is the age of becoming chair-bound. Electrocardiographic studies revealed no consistent abnormality and no evidence of an abnormal algebraic sum of the R and S waves in lead V1, as is found in patients with Duchenne muscular dystrophy. Serum creatine kinase levels are significantly elevated, particularly in the early stages of the disease, and in this way preclinical cases may be identified.

The myogenic scapulo-peroneal syndrome. Muscular dystrophy in the K. kindred: clinical study and genetics

Additional study was carried out of six generations belonging to the K. kindred, which were previously investigated by Oransky (1927). Eighteen members of this kindred were studied. In the early stages of the disease a sharp dissimilarity was observed in the phenotypes in the K. kindred, resulting from different rates of development and varying intensity in the course of the disease, so that it ranges from evident scapulo-peroneal amyotrophy to cases resembling Landouzy-Déjerine muscular dystrophy. In the later stages of the disease the clinical data on those affected were noted to be very similar. Muscular dystrophy in the K. kindred has been inherited as an autosomal-dominant type for five generations. The penetrance of the gene is almost complete. The expressivity of the gene varies from abortive to severe forms of disease. From the clinical and genetic data available at the present time, is seems that the muscular dystrophy in the K. kindred is one of the varieties (namely, a descending type with a "jump") of the facio-scapulo-limb (or facioscapulohumeral) muscular dystrophy. The scapulo-peroneal syndrome could be a long stage in the development of the disorder in some members of the K. kindred. As well as muscular dystrophy, some muscle anomalies have been independently inherited in the K. kindred. Apparently, muscular dystrophy and muscle defects are caused by the non-allele genes; this ensures the independent distribution of these signs among the members of the K. kindred.

Echocardiographic evaluation of posterior left ventricular wall motion in muscular dystrophy

Maximal systolic endocardial velocity (SEVM) and maximal diastolic endocardial velocity (DEVM) were determined echocardiographically in patients with muscular dystrophy (MD). The SEVM of the muscular dystrophy patients was 5.5 +/- 0.9 cm/sec and the DEVM was 13 +/- 3 cm/sec. The SEVM in MD was significantly less than that seen in age-matched normals (P less than 0.05), persons with myotonia congenita (P less than 0.02), deconditioned patients (P less than 0.001), or older normal persons (P less than 0.05). The Sevm of the MD patients was not significantly different from persons with spinal muscular atrophy. The DEVM of the muscular dystrophy patients was significantly less (P less than 0.001-0.05) than any other group. No correlation could be found between age, heart rate, type or severity of dystrophy and SEVM or DEVM values. The echocardiogram was more selective in correctly identigying muscular dystrophy patients than the electrocardiogram. The abnormality in DEVM was present despite lack of symptoms, normal cardiovascular examination, normal chest X-ray and normal electrocardiograms in 18 of 22 patients. We believe that the DEVM correlates with myocardial relaxation.