Advances in Dystrophinopathy Diagnosis and Therapy

Dystrophinopathies are x-linked muscular disorders which emerge from mutations in the Dystrophin gene, including Duchenne and Becker muscular dystrophy, and dilated cardiomyopathy. However, Duchenne muscular dystrophy interconnects with bone loss and osteoporosis, which are exacerbated by glucocorticoids therapy. Procedures for diagnosing dystrophinopathies include creatine kinase assay, haplotype analysis, Southern blot analysis, immunological analysis, multiplex PCR, multiplex ligation-dependent probe amplification, Sanger DNA sequencing, and next generation DNA sequencing. Pharmacological therapy for dystrophinopathies comprises glucocorticoids (prednisone, prednisolone, and deflazacort), vamorolone, and ataluren. However, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and β-blockers are the first-line to prevent dilated cardiomyopathy in dystrophinopathy patients. Duchenne muscular dystrophy gene therapy strategies involve gene transfer, exon skipping, exon reframing, and CRISPR gene editing. Eteplirsen, an antisense-oligonucleotide drug for skipping exon 51 from the Dystrophin gene, is available on the market, which may help up to 14% of Duchenne muscular dystrophy patients. There are various FDA-approved exon skipping drugs including ExonDys-51 for exon 51, VyonDys-53 and Viltolarsen for exon 53 and AmonDys-45 for exon 45 skipping. Other antisense oligonucleotide drugs in the pipeline include casimersen for exon 45, suvodirsen for exon 51, and golodirsen for exon 53 skipping. Advances in the diagnosis and therapy of dystrophinopathies offer new perspectives for their early discovery and care.

Lactate dehydrogenase isoenzymes in patients with acute exacerbation of chronic obstructive pulmonary disease: An exploratory cross-sectional study

We aimed to evaluate differences in serum lactate dehydrogenase (LDH) isoenzymes between patients hospitalized for acute exacerbation of chronic obstructive pulmonary disease (AECOPD) and other lower respiratory tract infections (LRTIs). Based on self-reported COPD diagnosis, 71 participants were divided into AECOPD (n = 38, 29 males, mean age 70.5 years) and LRTI (n = 33, 12 males, mean age 70.4 years) groups. Information on demographics, comorbidities, and COPD severity markers, as well as arterial blood gases and laboratory data were collected, while serum LDH electrophoresis was performed to examine the LDH isoenzymes. Adjusting for sex, age, comorbidities, degree of hypoxemia, inflammation markers, muscle and myocardial enzymes, and total serum LDH, the mean differences (95 % confidence intervals) in the ratios of serum LDH isoenzymes to total serum LDH between groups (LDHx_AECOPD - LDHx_LRTI) were statistically significant for LDH1 [4.9 (1.4 to 8.3)], LDH2 [3.0 (0.1 to 5.8)], LDH3 [-4.3 (-6.3 to -2.3)], and LDH4 [-3.2 (-4.9 to -1.5)]. A sum of LDH3 and LDH4 ratios below 29 % had the highest discriminative ability to classify a subject in the AECOPD group (AUC 0.841, sensitivity 76 %, specificity 87 %). Aerobic metabolic adaptive mechanisms in respiratory muscles during AECOPD could explain the above differences.

Enhanced dimethylarginine degradation improves coronary flow reserve and exercise tolerance in Duchenne muscular dystrophy carrier mice

Duchenne muscular dystrophy (DMD) is an X-linked disease caused by null mutations in dystrophin and characterized by muscle degeneration. Cardiomyopathy is common and often prevalent at similar frequency in female DMD carriers irrespective of whether they manifest skeletal muscle disease. Impaired muscle nitric oxide (NO) production in DMD disrupts muscle blood flow regulation and exaggerates postexercise fatigue. We show that circulating levels of endogenous methylated arginines including asymmetric dimethylarginine (ADMA), which act as NO synthase inhibitors, are elevated by acute necrotic muscle damage and in chronically necrotic dystrophin-deficient mice. We therefore hypothesized that excessive ADMA impairs muscle NO production and diminishes exercise tolerance in DMD. We used transgenic expression of dimethylarginine dimethylaminohydrolase 1 (DDAH), which degrades methylated arginines, to investigate their contribution to exercise-induced fatigue in DMD. Although infusion of exogenous ADMA was sufficient to impair exercise performance in wild-type mice, transgenic DDAH expression did not rescue exercise-induced fatigue in dystrophin-deficient male mdx mice. Surprisingly, DDAH transgene expression did attenuate exercise-induced fatigue in dystrophin-heterozygous female mdx carrier mice. Improved exercise tolerance was associated with reduced heart weight and improved cardiac β-adrenergic responsiveness in DDAH-transgenic mdx carriers. We conclude that DDAH overexpression increases exercise tolerance in female DMD carriers, possibly by limiting cardiac pathology and preserving the heart's responses to changes in physiological demand. Methylated arginine metabolism may be a new target to improve exercise tolerance and cardiac function in DMD carriers or act as an adjuvant to promote NO signaling alongside therapies that partially restore dystrophin expression in patients with DMD.NEW & NOTEWORTHY Duchenne muscular dystrophy (DMD) carriers are at risk for cardiomyopathy. The nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) is released from damaged muscle in DMD and impairs exercise performance. Transgenic expression of dimethylarginine dimethylaminohydrolase to degrade ADMA prevents cardiac hypertrophy, improves cardiac function, and improves exercise tolerance in DMD carrier mice. These findings highlight the relevance of ADMA to muscular dystrophy and have important implications for therapies targeting nitric oxide in patients with DMD and DMD carriers.

Duchenne Muscular Dystrophy: recent advances in protein biomarkers and the clinical application

INTRODUCTION

Early biomarker discovery studies have praised the value of their emerging results, predicting an unprecedented impact on health care. Biomarkers are expected to provide tests with increased specificity and sensitivity compared to existing measures, improve the decision-making process, and accelerate the development of therapies. For rare disorders, like Duchenne Muscular Dystrophy (DMD) such biomarkers can assist the development of therapies, therefore also helping to find a cure for the disease.

AREA COVERED

State-of-the-art technologies have been used to identify blood biomarkers for DMD and efforts have been coordinated to develop and promote translation of biomarkers for clinical practice. Biomarker translation to clinical practice is however, adjoined by challenges related to the complexity of the disease, involving numerous biological processes, and the limited sample resources. This review highlights the current progress on the development of biomarkers, describing the proteomics technologies used, the most promising findings and the challenges encountered.

EXPERT OPINION

Strategies for effective use of samples combined with orthogonal proteomics methods for protein quantification are essential for translating biomarkers to the patient's bed side. Progress is achieved only if strong evidence is provided that the biomarker constitutes a reliable indicator of the patient's health status for a specific context of use.

Comparative effects of Mancozeb and Disulfiram-induced striated muscle myopathies in Long-Evans rats

Dithiocarbamates (DTCs) like mancozeb (MZ) and disulfiram (DS) are used throughout agriculture and medicine and have been implicated in neurotoxicity. Little research has been studied on the reported myopathies caused by these compounds. Their pathogenesis and mechanism of muscle toxicity has not been fully studied. The aim of this study is to investigate if DTCs alter striated muscle tissues in vivo. Long-Evans rats were treated with either MZ or DS followed by analysis of muscle biomarkers and metal levels. DS resulted in increases in serum lactate dehydrogenase (LDH), cardiac troponin, and myoglobin levels. Creatine kinase-MB serum levels decreased. Mancozeb only showed an increase in serum LDH. Both MZ and DS-treatment resulted in altered metal levels in the myocardium but not skeletal muscle. Ultrastructural alterations included damaged mitochondria and myofibril splitting. The presence of multivesicular bodies, and alterations of the intercalated disc were also seen.

Placebo-controlled Phase 2 Trial of Drisapersen for Duchenne Muscular Dystrophy

Objective

This double‐blind, randomized, placebo‐controlled Phase 2 study (NCT01462292) assessed the 24‐week efficacy, safety, tolerability, and pharmacokinetics of two different subcutaneous drisapersen doses, and the 24‐week off‐dose persistent effect, in ambulant Duchenne muscular dystrophy (DMD) patients.

Methods

Male DMD patients (≥5 years; time to rise from floor ≤15 s) were randomized to drisapersen 3 mg/kg/week, 6 mg/kg/week or placebo. The primary efficacy endpoint was change from baseline in 6‐minute walking distance (6MWD) at week 24. Secondary endpoints included changes in timed function tests, muscle strength, and pulmonary function tests.

Results

Fifty‐one patients were randomized to placebo (N = 16), drisapersen 3 mg/kg/week (N = 17) or 6 mg/kg/week (N = 18). All but 2 patients had baseline rise from floor time <7 s. This study was exploratory and not prospectively powered; however, a difference in mean 6MWD versus placebo in favor of drisapersen 6 mg/kg/week was observed at week 24 (27.1 m; P = 0.069) and maintained 24 weeks off‐treatment (27.9 m; P = 0.177). The 3 mg/kg/week group showed no statistically significant difference in mean 6MWD versus placebo. For some secondary endpoints, a more positive response in favor of drisapersen 6 mg/kg/week compared to placebo was shown. Drisapersen had a long half‐life with steady state reached after approximately 36 weeks. Most common adverse events in both drisapersen groups were related to injection site reactions and subclinical proteinuria.

Interpretation

Drisapersen 6 mg/kg/week for 24 weeks resulted in a treatment benefit in 6MWD, largely maintained 24 weeks off‐treatment. This study provided insights for further studies to optimize dosage regimen.

A randomized placebo-controlled phase 3 trial of an antisense oligonucleotide, drisapersen, in Duchenne muscular dystrophy

This 48-week, randomized, placebo-controlled phase 3 study (DMD114044; NCT01254019) evaluated efficacy and safety of subcutaneous drisapersen 6 mg/kg/week in 186 ambulant boys aged ≥5 years, with Duchenne muscular dystrophy (DMD) resulting from an exon 51 skipping amenable mutation. Drisapersen was generally well tolerated, with injection-site reactions and renal events as most commonly reported adverse events. A nonsignificant treatment difference (P = 0.415) in the change from baseline in six-minute walk distance (6MWD; primary efficacy endpoint) of 10.3 meters in favor of drisapersen was observed at week 48. Key secondary efficacy endpoints (North Star Ambulatory Assessment, 4-stair climb ascent velocity, and 10-meter walk/run velocity) gave consistent findings. Lack of statistical significance was thought to be largely due to greater data variability and subgroup heterogeneity. The increased standard deviation alone, due to less stringent inclusion/exclusion criteria, reduced the statistical power from pre-specified 90% to actual 53%. Therefore, a post-hoc analysis was performed in 80 subjects with a baseline 6MWD 300-400 meters and ability to rise from floor. A statistically significant improvement in 6MWD of 35.4 meters (P = 0.039) in favor of drisapersen was observed in this subpopulation. Results suggest that drisapersen could have benefit in a less impaired population of DMD subjects.

Low intensity training of mdx mice reduces carbonylation and increases expression levels of proteins involved in energy metabolism and muscle contraction

High intensity training induces muscle damage in dystrophin-deficient mdx mice, an animal model for Duchenne muscular dystrophy. However, low intensity training (LIT) rescues the mdx phenotype and even reduces the level of protein carbonylation, a marker of oxidative damage. Until now, beneficial effects of LIT were mainly assessed at the physiological level. We investigated the effects of LIT at the molecular level on 8-week-old wild-type and mdx muscle using 2D Western blot and protein-protein interaction analysis. We found that the fast isoforms of troponin T and myosin binding protein C as well as glycogen phosphorylase were overcarbonylated and downregulated in mdx muscle. Some of the mitochondrial enzymes of the citric acid cycle were overcarbonylated, whereas some proteins of the respiratory chain were downregulated. Of functional importance, ATP synthase was only partially assembled, as revealed by Blue Native PAGE analysis. LIT decreased the carbonylation level and increased the expression of fast isoforms of troponin T and of myosin binding protein C, and glycogen phosphorylase. In addition, it increased the expression of aconitate hydratase and NADH dehydrogenase, and fully restored the ATP synthase complex. Our study demonstrates that the benefits of LIT are associated with lowered oxidative damage as revealed by carbonylation and higher expression of proteins involved in energy metabolism and muscle contraction. Potentially, these results will help to design therapies for DMD based on exercise mimicking drugs.

Serum Enzyme Profiles Differentiate Five Types of Muscular Dystrophy

Background. Differentiation among types of muscular dystrophy (MD) has remained challenging. In this retrospective study, we sought to develop a methodology for differentiation of MD types using analysis of serum enzyme profiles. Methods. The serum levels of enzymes from 232 patients, including 120 with DMD, 36 with BMD, 36 with FSHD, 46 with LGMD, and 11 with EDMD, were evaluated. Results. The characteristic profiles of serum enzymes facilitated differentiation of these five types of MD. DMD was characterized by simultaneous elevation of ALT, AST, LDH, and ALP; BMD and LGMD were characterized by elevation of ALT, AST, and LDH; and FSHD and EDMD were characterized by a lack of abnormal serum enzyme levels. We further developed discriminant functions to distinguish BMD and LGMD. For LGMD, LGMD2B patients had significantly higher ALP levels than non-LGMD2B patients (98 ± 59 U/L versus 45 ± 9 U/L, resp., p < 0.05). Conclusions. Our approach enabled the determination of MD subtypes using serum enzyme profiles prior to genetic testing, which will increase the chance a mutation will be found in the first gene analyzed.

Enzyme activities in serum after extensive exercise, with special reference to creatine kinase MB

It is well documented that elevations of serum enzymes used as criteria in establishing the diagnosis of acute myocardial infarction (AMI) often show a pattern of AMI after physical exercise without other clinical signs of myocardial damage. Since a clinical condition resembling AMI sometimes appears after strenuous physical exercise, this study was designed to show if the new, almost heart-specific, isoenzyme creatine kinase MB (CK-MB) would solve the diagnostic problems. Ten well trained volunteers took part in a 26 km jogging race. None of them had any cardiovascular symptoms, but the 'old' cardiac enzymes rose in some of them above the discriminatory levels, whereas CK-MB was below these levels in all cases. It is concluded that CK-MB determination is a valuable diagnostic tool, also in patients who have recently exercised extensively.

A Comparison of Breast Muscle Characteristics in Three Broiler Great-Grandparent Lines

Genetic selection of broiler chickens has led to a gross overdevelopment of the broiler breast muscle pectoralis major. This may have resulted in increased myopathy and detrimental effects on meat quality. The present study examined 3 commercial great-grandparent lines (lines A, B, and C). Lines A and B are female lines, and line C is a male line. The mean BW of line C (2.7 kg) was significantly greater than those of lines A and B (both 2.3 kg). However, the mean breast yield of both lines B and C (8.9 and 8.7%, respectively) was significantly greater than that of line A (6.9%). Line B therefore matched the meat yield of line A while maintaining a high reproductive capacity. The mean breast fillet weight of line A (169 g) was significantly lower than lines B (207 g) and C (235 g). No differences were observed between lines in either mean fiber size or amount of connective tissue. Therefore, additional fibers must provide the additional weight in the breast fillet of lines B and C, compared with A. Plasma creatine kinase activity, a commonly used marker of muscle damage, was significantly higher in line A (1368 IU/L) than in lines B (995 IU/L) and C (982 IU/L). However, qualitative evaluations of muscle pathology revealed no differences among lines. Selection for increased embryonic muscle fiber number, rather than for increased radial fiber growth, could improve growth potential and may also alleviate muscle damage.

Evaluation of Lactate and C-Reactive Protein in the Assessment of Acute Myocardial Infarction

PURPOSE

The purpose of this study was to assess the usefulness of lactate and C-reactive protein as early markers of acute myocardial infarction (AMI) in conjunction with established markers, such as creatine phosphokinase (CPK)-MB and troponin I.

METHODS

The study population consisted of all patients admitted with suspected AMI regardless of age, race, gender, or comorbid conditions. All patients in cardiac heart failure or cardiogenic shock were excluded. Lactate and C-reactive protein were drawn at admission, and then at 2 and 4 hours, respectively. The positive and negative predictive values of these markers were calculated in relation to the primary outcome measure.

RESULTS

A total of 62 patients were enrolled in the study. Of those, 18 patients had documented AMI and all underwent thrombolysis, thrombolysis with angioplasty, or stent placement. The lactate was measured at 2 and 4 hours, and lactate levels correlated with CPK and CPK-MB, in addition to troponin I. In our cohort, lactate had a sensitivity of 75% and a specificity of 95.5%, with a positive predictive value of 85.7% and a negative predictive value of 91.3%.

CONCLUSION

As an inexpensive and readily available marker for AMI, lactate seems to be reliable and could be used in an emergency setting to facilitate the decision-making process for chest pain syndrome. It would be a helpful adjunct on whether the patient can be safely discharged or should be promptly admitted.

Cardiac involvement in myositis

After careful examination, cardiac involvement can be found in certain patients with inflammatory muscle disease. The clinical significance is not always clear, although in some patients profound disturbances can become manifest. Currently, no laboratory assay can be relied on to detect cardiac disease with 100% accuracy. Cardiac troponin I is, however, the best test currently available.

Lactate dehydrogenase (LD) pattern in serum of calves with a total artificial heart (TAH)

Serum lactate dehydrogenase (LD) patterns of 16 calves with total artificial heart (TAH) were studied to identify a mean LD pattern in their serum (survival 51–293 days). Evaluations were made by the sum of vectors method (SV). The mean LD pattern was determined from serum LD patterns, interval days of 33 - 49 with TAH. Serum LD patterns of control and mean LD pattern differed significantly (n = 12, P < 0.05) in single isoenzymes and resultant vectors as the representatives of LD patterns. The different tissues with an increased risk of being affected were identified by evaluation of LD patterns in the serum of calves within term without perceptible acute damage and in the terminal stage of experiments. Such identified organs suggest that the organism under study is out of balance and specific treatment is needed.

Use of a rapid assay of subforms of creatine kinase MB to diagnose or rule out acute myocardial infarction

BACKGROUND

Ruling out myocardial infarction in patients coming to the emergency room with chest pain is hindered by the lack of a specific early diagnostic marker. Less than 30 percent of patients admitted to coronary care units have infarction, resulting in substantial unnecessary expenditures. We developed a rapid assay of the subforms of creatine kinase MB (CK-MB) and prospectively analyzed its sensitivity and specificity in diagnosing myocardial infarction in the first six hours after the onset of chest pain.

METHODS

In 1110 consecutive patients who came to the emergency room with chest pain, blood samples were collected every 30 to 60 minutes until at least 6 hours after the onset of symptoms; in patients who were then admitted to the hospital, samples were collected every 4 hours for up to 48 hours. The samples were analyzed for CK-MB subforms, and the diagnosis of myocardial infarction was confirmed by conventional CK-MB analysis.

RESULTS

Of the 1110 patients evaluated, 121 had myocardial infarction. The sensitivity of the assay of CK-MB subforms to detect myocardial infarction in the first six hours after the onset of symptoms was 95.7 per cent, as compared with only 48 percent for the conventional CK-MB assay; the specificity was 93.9 percent among patients hospitalized without myocardial infarction and 96.2 percent among those sent home. Among the patients with myocardial infarction, definitive results of the subform assay were available a mean (+/- SD) of 1.22 +/- 1.17 hours after their arrival in the emergency room.

CONCLUSIONS

The assay of CK-MB subforms reliably detected myocardial infarction within the first six hours after the onset of symptoms, and its use could reduce admission to the coronary care unit by 50 to 70 percent, thereby reducing costs.

Muscular sufficiency, serum protein, enzymes and bioenergetic studies (31-phosphorus magnetic resonance spectroscopy) in chronic malnutrition

Muscle sufficiency was significantly lower in 1336 children with chronic malnutrition of moderate to severe degree. Eighteen children with a chronic moderate degree of malnutrition and 8 well-nourished, age-matched controls were selected for biochemical and 31-phosphorus magnetic resonance spectroscopy (31-P MRS) studies. The results showed that: (a) serum total protein, albumin, iron, calcium and inorganic phosphate were similar in both groups; (b) serum enzyme levels were significantly increased in the malnourished group; (c) 31-P MRS showed significantly higher means for total ATP, beta-ATP, alpha-ATP and inorganic phosphate for the malnourished compared to the control group. In chronic malnutrition, proteins are maintained by degradation in muscle resulting in release of amino acids and enzymes. 31-P MRS studies showing increases in total ATP, beta-ATP and inorganic phosphate and a decrease in phosphocreatine suggest that ATP is maintained at the cost of phosphocreatine.

Geographic distribution of xanthine oxidase, free radical scavengers, creatine kinase, and lactate dehydrogenase enzyme systems in rat heart and skeletal muscle

The geographic distribution of the following enzyme systems is described in the rat heart (left and right ventricles) and in different skeletal muscles (soleus, plantaris, and red and white gastrocnemius): xanthine oxidase and dehydrogenase, creatine kinase isoenzymes, lactate dehydrogenase isoenzymes, and the free radical scavenger enzymes superoxide dismutase, glutathione reductase, and glutathione peroxidase. No substantial difference in enzyme activities was observed between the left and right ventricles. Skeletal muscles showed a clear distinction between enzyme activities depending on their composition of oxidative fibers and glycolytic fibers.

Skeletal muscle CK-B activity in neurogenic muscular atrophies

Creatine kinase isoenzymes were determined in skeletal muscle biopsy specimens of 34 patients suffering from neurogenic muscular atrophies. The findings were compared: (1) with those of 38 control muscle samples and (2) with those in 41 muscular dystrophies and other myopathic conditions. The measurements were made by electrophoretic separation and elution of the isoenzymes and by immunoinhibition assay. The results showed that the total and specific CK activity were significantly decreased (P less than 0.005) in neurogenic atrophies in contrast to myopathic conditions where no differences from control levels were observed. This decrease was due to a decrease of the CK-M subunit activity, while the CK-B subunit was elevated. The muscle CK-MB activity was considerably elevated in muscular dystrophies (P less than 0.02) and myositis (P less than 0.001), but it was also slightly elevated in neurogenic conditions. The similarity of the muscle CK isoenzyme pattern in neurogenic atrophies and myotonic dystrophy was noted. These findings could possibly reflect considerable difference in the regeneration process of neurogenic atrophies and muscular dystrophies.

Changes in serum enzymes, lactate, and haptoglobin following acute physical stress in international-class athletes

Skeletal muscle is rich in creatine kinase (CK), lactate dehydrogenase (LD), and other enzymes. Many reports describe changes in serum CK and LD following exercise. In our study, 11 male international-class medium-distance runners were followed over a 10-month period prior to the 1984 US Olympic Trials. Cardiorespiratory fitness, evaluated through repetitive treadmill testing, was unchanged in our athletes. Total CK increased significantly during the course of training, and the CK-MB activity was higher than that of sedentary individuals; CK-MB never rose to more than 3% of the total CK. Total LD also rose following acute exercise; however, the proportions of the five isoenzymes were unaltered. There was no change in the LD-1/LD-2 ratio from normal. The origin of the increased serum enzymes was believed to be primarily skeletal muscle. A decrease of serum haptoglobin following acute stress was attributed to intravascular hemolysis and binding of hemoglobin. As expected, serum lactate was dramatically increased immediately postexercise.

Juvenile dermatomyositis

Myositis in childhood is characterized by elevated serum levels of muscle-derived enzymes, proximal symmetrical muscle weakness, abnormal EMG findings, and a muscle biopsy, which frequently documents an inflammatory process. In the pediatric age group, JDMS, which has characteristic cutaneous involvement in addition to myositis, is much more common than PM and is more common among female patients. With the use of steroids, mortality has been reduced from 33 per cent to 7 per cent. The development of calcifications can be the most debilitating consequence of JDMS. It is our premise that JDMS is a distinct disease entity and that the increase in HLA-B8 and DR3 in JDMS suggests that genetic background may predispose to disease development. There are conflicting data concerning immunologic abnormalities in JDMS, but there appears to be impairment of natural killing and evidence of complement activation. Results of tests for ANA frequently are positive in JDMS, but Jo-1 antibody, found in some adults with PM, has not been found in JDMS. Most newly diagnosed JDMS patients have antibodies to coxsackie B that may be related to the pathogenesis of this disease. Specific pathologic findings of endothelial cells containing reticulotubular inclusions are associated with small vessel occlusion, subsequent obliteration, and increased factor VIII levels in clinically active disease. In addition to physical therapy, steroids are used most frequently, but other immunosuppressive agents and plasmapheresis have been tried in severely ill children. Rigorous evaluation of the efficacy of these modalities is needed.

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.

The diagnostic value of different enzymes and standard ECG in acute myocardial infarction

Serum (S) enzyme activity of aspartate aminotransferase (ASAT, E.C. 2.6.1.1.), heat stable lactate dehydrogenase (LD, E.C. 1.1.1.27.), creatine kinase (CK, E.C. 2.7.3.2.) and CK-B subunit and the respective standard electrocardiograms (ECG) were compared in 463 patients with suspected acute myocardial infarction (MI) in order to evaluate sensitivity and specificity. Serum ASAT was analysed daily for 3 days, S-heat stable LD every 12 h for 48-108 h, S-CK and S-CK-B every 6 h for 48 h and ECG once daily for 3 days. All four enzymes had a high sensitivity, varying from 99% for LD to 97% for CK-B. The highest specificity was observed for CK-B and CK (98%) as compared with heat stable LD (91%) and ASAT (74%). Standard ECG showed a high specificity (96%) and a low sensitivity (80%).

Serum enzyme determinations in the diagnosis of acute myocardial infarction: an update

Serum CK-MB and LD-1 have proved extremely useful in the diagnosis and differential diagnosis of acute myocardial infarction. However, CK-MB is present in skeletal muscle and can be released during ischemic attacks; thus, abnormal serum CK-MB activities cannot be equated with myocardial injury. Even wider is the distribution of LD-1, which is found particularly in erythrocytes and renal cortex; hence, an abnormal LD-1 level also cannot be equated with myocardial injury. The method of choice and the final arbiter for the CK and LD isoenzymes is electrophoresis. The possibility of interpreting the results visually fulfills, in part, quality-control needs, and makes the technique suitable for small and large laboratories. Extreme analytic sensitivity is not needed, and electrophoresis provides clinically useful and acceptable results.

Duchenne muscular dystrophy: pathogenetic aspects and genetic prevention

Duchenne muscular dystrophy (DMD) is the most common sex linked lethal disease in man (one case in about 4000 male live births). The patients are wheelchair bound around the age of 8-10 years and usually die before the age of 20 years. The mutation rate, estimated by different methods and from different population studies, is in the order of 7 X 10(-5), which is higher than for any other X-linked genetic disease. Moreover, unlike other X linked diseases such as hemophilia A or Lesh-Nyhan's disease, there seems to be no sex difference for the mutation rates in DMD. Several observations of DMD in girls bearing X-autosomal translocations and linkage studies on two X chromosomal DNA restriction fragment length polymorphisms indicate that the DMD locus is situated on the short arm of the X chromosome, between Xp11 and Xp22. It may be of considerable length, and perhaps consisting of actively coding and non-active intervening DNA sequences. Thus unequal crossing over during meiosis in females could theoretically account for a considerable proportion of new mutations. However, there is no structurally or functionally abnormal protein known that might represent the primary gene product, nor has any pathogenetic mechanism leading to the observed biochemical and histological alterations been elucidated. Among the numerous pathogenetic concepts the hypothesis of a structural or/and functional defect of the muscular plasma membrane is still the most attractive. It would explain both the excess of muscular constituents found in serum of patients and carriers, such as creatine kinase (CK), as well as the excessive calcium uptake by dystrophic muscle fibres, which, prior to necrosis, could lead to hypercontraction, rupture of myofilaments in adjacent sarcomeres and by excessive Ca uptake to mitochondrial damage causing crucial energy loss. The results of studies on structural and functional membrane abnormalities in cells other than muscle tissue, e.g., erythrocytes, lymphocytes and cultured fibroblasts, indicate that the DMD mutation is probably demonstrable in these tissues. However, most of the findings are still difficult to reproduce or even controversial. DMD is an incurable disease; therefore most effort, in research as well as in practical medicine, is concentrated upon its prevention.(ABSTRACT TRUNCATED AT 400 WORDS)

Alterations in creatine kinase, ornithine decarboxylase, and transglutaminase during muscle regeneration

Creatine kinase (CK), transglutaminase (TGase) and ornithine decarboxylase (ODC), enzymes implicated in the regulation of growth processes, were studied during muscle regeneration subsequent to the injection of bupivacaine into rat tibialis anterior. Within 2 days, the percent BB isozyme of CK detected in the muscle was elevated 70-fold coincident with a marked decrease in total CK activity. The MB isozyme also increased and was 15-fold of control at 4-5 days postinjection. TGase activity was increased significantly to greater than 2-fold of control within 2 days of injection and significantly decreased at days 3 through 7 compared to controls. ODC activity was elevated significantly to 2- to 3-fold of control from 2-7 days after injection. These results suggest an early alteration in the expression of a coordinated battery of genes in this model of muscle degeneration-regeneration. The increased expression of MB and BB isozymes of CK in various human neuromuscular diseases may be a manifestation of an ongoing process of degeneration-regeneration.

The enzymology of skeletal muscle disorders

In myopathic disorders, abnormal serum enzyme activities are seen primarily in diseases of skeletal muscle where the condition involves the muscle fibers themselves. In denervation myopathies, serum enzyme activities are usually normal. The most dramatic increases of serum enzymes, particularly creatine kinase, are found in the dystrophic diseases, particularly Duchenne dystrophy. A review is given here of the many causes of abnormal serum enzyme activities where the source of enzymes is believed to be skeletal muscle. These include the dystrophies, various types of trauma, exercise, drug- and poison-induced causes including alcohol, malignant hyperthermia, inflammatory diseases, and miscellaneous causes. Tissue and serum activities are summarized for the commonly performed serum enzymes, i.e., CK, LD, AST, and aldolase. An extensive tabular and current description of the various types of dystrophies is given along with serum CK and pyruvate kinase activities.

Duchenne muscular dystrophy carrier detection using logistic discrimination: serum creatine kinase, hemopexin, pyruvate kinase, and lactate dehydrogenase in combination

In the absence of an unambiguous test for identifying Duchenne muscular dystrophy (DMD) heterozygotes, methods are needed for combination of the results of individually equivocal tests as effectively and rationally as possible. Tw used logistic discrimination to assess the effectiveness of measurements of serum creatine kinase, hemopexin, pyruvate kinase, and lactate dehydrogenase alone and in various combinations in identifying DMD carriers. We analyzed 127 serum samples from 63 normal female controls (20-40 years old) and 67 from 38 obligate DMD carriers. The best two tests to use in combination were creatine kinase and hemopexin, and these two, with lactate dehydrogenase, were the best three. t the 95% level (with 5% of controls misclassified), 54% of the carriers were identified by CK alone, whereas 88% were identified by means of the four tests. Although a small proportion of known carriers still cannot be identified, application of the four tests to a group of 45 possible carrier mothers of isolated cases of DMD resolves the population into fairly discrete "normal" and "abnormal" subgroups. Thus, if bias of selection can be eliminated, application of logistic discrimination may permit a direct estimate of the proportion of mothers of affected boys who are homozygous normal.

Significance of serum myoglobin in neuromuscular diseases and in carrier detection of Duchenne muscular dystrophy

In a retrospective study, the serum myoglobin concentration (S-myoglobin) was determined in patients with neuromuscular diseases and in carriers of Duchenne muscular dystrophy (DMD). Myoglobin was quantified by a sensitive radioimmunoassay. Serum creatine kinase (CK, EC 2.7.3.2) activity (S-CK) and serum creatine kinase B-subunit activity (S-CKB) were determined for comparison. Sera from 70 patients with various neuromuscular diseases and from 17 female relatives of patients with DMD were analysed. Increased levels of S-myoglobin were found both in dystrophic and in spinal myopathies. Because of a marked overlap of the range of values between the different dystrophic myopathies and even between the dystrophic and the spinal myopathies, S-myoglobin is of little value in the final diagnosis of neuromuscular diseases. In the detection of carriers of DMD, simultaneous determination of S-myoglobin and S-CK gave a higher detection rate compared to the detection rate with S-CK. S-CKB was normal in all carriers and only elevated in some of the patients with DMD and limb girdle muscular dystrophy.

Muscle cell leakage due to long distance training

Abnormal myoglobinemia (above 77 microgram/l) and free hemoglobin in plasma were found in 16 runners and in nine non runners immediately following distance running. The same abnormalities were found iun six elite rowers following rowing. In parallel with the rise in myoglobin and free hemoglobin a rise was found in serum concentrations of cellular enzymes (LDH, CK, ASAT, alkaline phosphatase) and of various metabolites. We found no proteinuria nor casts in the urine. Non runners had a higher rise in serum myoglobin than runners. Competitive running caused a rise in the serum concentration of the heart specific fraction of creatine kinase in seven of the nine (healthy) elite runners. The abnormal findings are only explainable on the basis of leakage of proteins from muscle cells to the circulation in otherwise healthy, well trained persons. Myoglobinemia and a transient rhabdomyolysis is a common phenomenon in long distance running, but evidently also occurs in distance rowing. Three months of running training prevented most of the muscle damage from relaxed jogging in the nine previous non runners. Neither the observed myoglobinemia nor the hemoglobinemia resulted in any significant loss of iron in the urine.

Creatine kinase isozyme transition in chicks with hereditary muscular dystrophy

In both normal chicks and chicks with hereditary muscular dystrophy the BB (brain) and MB (hybrid) isozymes were the predominant forms of creatine kinase (CK) activity in embryonic skeletal muscle. As myogenesis progressed, activity due to the MM (muscle) isozyme progressively increased, and by 1 week ex ovo, the MM isozyme accounted for approximately 97% of total muscle activity in both genotypes. During this time, the proportion of the MM isozyme was slightly but significantly lower in dystrophic muscles. After hatching the proportion of the MB isozyme and its total activity decreased in normal muscle, but increased in dystrophic pectoral muscle, and by 5 months ex ovo, the MB isozyme accounted for 10% of total CK activity. Prior to hatching there was no consistent difference in total CK activity between normal and dystrophic tissues, but by 1 week after hatching and thereafter, total CK activity was significantly lower in dystrophic pectoral muscle.

Diagnostic significance of serum CK-MB elevations following surgical damage to skeletal muscles

Total creatine kinase (CK) and its isoenzyme MB (CK-MB) were studied in the serum of 14 patients following thoracotomy, mostly for pulmonary surgery, and in various thoracic muscles from another 9 patients subjected to the same procedure. CK-MB consistently appeared in the serum and was present in all muscle samples examined. CK-MB as a percentage of total CK (the CK-MB/CK ratio) was of similar order in serum and muscle, approximately 1.5%. Compared with previous findings after cardiopulmonary bypass surgery, maximum serum CK-MB activity occurred later, and the CK-MB levels as well as the CK-MB/CK ratio were considerably lower after non-cardiac thoracic surgery. It is suggested that the CK-MB/CK ratio 24 hours after operation may be used in the diagnosis of peri-operative myocardial infarction, particularly in non-cardiac surgery. After thoracotomy, this ratio was below 2.2%. In a series of patients with acute myocardial infarction, reported previously, the ratio was above 5.4%. Secondary rises of serum CK-MB following cardiac surgery should, apparently also be analysed in relation to the simultaneous total CK level.

Serum creatine kinase BB and MM concentrations determined by radioimmunoassay in neuromuscular disorders

We measured the MM and BB isoenzymes of serum creatine kinase (CK) by radioimmunoassay in 89 patients with neuromuscular disorders and 44 definite or possible carriers of Duchenne muscular dystrophy (DMD). The CK-MM isoenzyme was closely associated with total CK enzymatic activity. CK-BB was not as closely correlated with total CK but was usually increased in the inflammatory myopathies and DMD and normal in myasthenia gravis, Guillain-Barré syndrome, and amyotrophic lateral sclerosis as well as in neuropathies in which CK is usually normal. In myopathies, CK-BB may be useful for assessing the level of disease activity or the regenerative component. More study is necessary to assess the role of CK-BB in detection of DMD carriers.

Early changes of muscle mitochondria in Duchenne dystrophy. Partition and activity of mitochondrial enzymes in fractionated muscle of unaffected boys and adults and patients

(1) Biopsies from the gastrocnemius muscle of patients with Duchenne dystrophy were partitioned into a myofibrillar plus nuclear fraction, a mitochondrial fraction and a supernatant fraction. The fractions were assayed for mitochondrial enzymes and protein, in order to obtain information about the integrity of mitochondrial structure and function. Muscles from boys and adults without neuromuscular disease were treated likewise. (2) In adults, muscle possesses a significantly higher specific activity (on protein basis) of monoamine oxidase and rotenone-insenitive NADH-cytochrome c reductase (RINCR) than in boys. In childhood, monoamine oxidase activity increases with age. At the age of 5 yr, the specific activity is 50% of the adult value. RINCR activity is constant in childhood. With adolescence it increases from 20 +/- 2 (SEM) to 35 +/- 6 mumoles cytochrome c reduced per min per g protein, and it remains at this level. Palmitoyl-CoA synthetase activity remains constant with age. (3) In Duchenne dystrophy the extractable protein content from muscle is decreased to 75%. The specific activities of the matrix enzymes propionyl-CoA carboxylase and glutamate dehydrogenase are 1.8 and 2.8 times increased, the inner membrane enzyme cytochrome c oxidase is 2.8 times increased, the inner membrane enzyme cytochrome c oxidase is 2.8 times increased. Of the outer membrane enzymes RINCR is 2.0 times increased, while palmitoyl-CoA synthetase is not changed in acitivity. In Duchenne dystrophy monoamine oxidase activity also increases with age. In part this may be due to mitochondria from adipose tissue and macrophages, which are increasingly present in older patients. The specific activities of enzymes with a predominant cytosolic localisation, creatine kinase and adenylate kinase, are increased by a factor of 1.5 and 1.7. (4) The subcellular distribution of the studied enzymes in human skeletal muscle was found to be similar as in animal studies. In mitochondrial fractions from Duchenne patients the recoveries of the following enzymes are decreased: glutamate dehydrogenase (from 25 to 9%), creatine kinase (1.1-0.66%), adenylate kinase (0.44-0.22%), hexokinase (7.1-2.7%), monoamine oxidase (36-21%), RINCR (30-17%), and palmitoyl-CoA synthetase (40-21%). The recoveries of last 3 mitochondrial outer membrane enzymes in the supernatant fractions are correspondingly increased. These results indicate an increased fragility of the mitochondrial membranes in dystrophic muscles. (5) The reported changes are clearly evident in a one-year-old patient, which indicates that the mitochondria are involved early in the disease process.

Epidemic influenza myopathy in Cincinnati in 1977

A distinctive myopathy was observed in 24 children following influenza B infection. The abrupt onset of severe muscle pain and difficulty in walking began as the respiratory symptoms were waning. The lower extremities, particularly the gastrocnemius and soleus muscles, were involved preferentially. Nasopharyngeal cultures were positive for influenza B Hong Kong in 18 of these patients. Serum creatine phosphokinase levels were significantly elevated (mean 55.2 units) when compared to controls and nine patients with Reye syndrome. The cardiac muscle isoenzyme was detected in the serum of 17 myopathy patients. Serum glutamic oxaloacetic transaminase, but not serum glutamic pyruvic transaminase, was elevated compared to controls (P less than 0.01) but less (P less than 0.001) than the patients with Reye syndrome. Twelve patients underwent muscle biopsy; segmental rhabdomyolysis without inflammation was detected in nine patients. Myopathy is a complication of influenza infection that can be diagnosed by clinical, biochemical, and virologic examination.

Biochemistry of muscle membranes in Duchenne muscular dystrophy

In Duchenne muscular dystrophy, as in other genetic diseases, there must be a biochemical abnormality. This fundamental genetic fault has not been identified, but several indirect lines of evidence suggest that the surface membranes of skeletal muscle are affected. The biochemical evidence implies abnormal egress of soluble enzymes and other proteins from muscle, abnormal permeability, and altered properties of membrane-bound enzymes. As a result of the presumed genetic abnormality, functional properties are altered, and impaired regulation of intracellular calcium content could be responsible for the hallmarks of the disease--progressive weakness and degeneration of muscle. The evidence is by no means conclusive, however, and some of it is contradictory. Technical advances must be made before isolated membranes can be characterized biochemically. Other theories are also being evaluated.