Congenital myopathies at their molecular dawning.

The introduction and application of molecular techniques have commenced to influence and alter the nosology of congenital myopathies. Long-known entities such as nemaline myopathies, core diseases, and desmin-related myopathies have now been found to be caused by unequivocal mutations. Several of these mutations and their genes have been identified by analyzing aggregates of proteins within muscle fibers as a morphological hallmark as in desminopathy and actinopathy, the latter a subtype among the nemaline myopathies. Immunohistochemistry has played a crucial role in recognizing this new group of protein aggregate myopathies within the spectrum of congenital myopathies. It is to be expected that other congenital myopathies marked by inclusion bodies may turn out to be such protein aggregate myopathies, depending on analysis of individual proteins within these protein aggregates and their association with putative gene mutations.     

Protein aggregate myopathies

Protein aggregate myopathies (PAM) are an emerging group of muscle diseases characterized by structural abnormalities. Protein aggregate myopathies are marked by the aggregation of intrinsic proteins within muscle fibers and fall into four major groups or conditions: (1) desmin-related myopathies (DRM) that include desminopathies, a-B crystallinopathies, selenoproteinopathies caused by mutations in the, a-B crystallin and selenoprotein N1 genes, (2) hereditary inclusion body myopathies, several of which have been linked to different chromosomal gene loci, but with as yet unidentified protein product, (3) actinopathies marked by mutations in the sarcomeric ACTA1 gene, and (4) myosinopathy marked by a mutation in the MYH-7 gene. While PAM forms 1 and 2 are probably based on impaired extralysosomal protein degradation, resulting in the accumulation of numerous and diverse proteins (in familial types in addition to respective mutant proteins), PAM forms 3 and 4 may represent anabolic or developmental defects because of preservation of sarcomeres outside of the actin and myosin aggregates and dearth or absence of other proteins in these actin or myosin aggregates, respectively. The pathogenetic principles governing protein aggregation within muscle fibers and subsequent structural sarcomeres are still largely unknown in both the putative catabolic and anabolic forms of PAM. Presence of inclusions and their protein composition in other congenital myopathies such as reducing bodies, cylindrical spirals, tubular aggregates and others await clarification. The hitherto described PAMs were first identified by immunohistochemistry of proteins and subsequently by molecular analysis of their genes.     

Emerging toxic neuropathies and myopathies

There is a daunting list of toxins that can affect the peripheral nervous system, with new drugs and chemicals added to this list every year. This article focuses on some of the more recent toxic neuropathies and myopathies that have emerged from the medical literature. Among these are toxic myopathies caused by statins, daptomycin, imatinib, hydroxychloroquine, and highly active antiretroviral therapy; neuromuscular junction toxicity caused by tandutinib; toxic peripheral neuropathies caused by bortezomib, angel's trumpet, cisplatin, oxaliplatin, tumor necrosis factor α antagonists, cobalt-chromium, and ixabepilone; and a unique syndrome reported in workers exposed to aerosolized porcine neural tissue.     

Short-term aerobic training response in chronic myopathies.

We have previously demonstrated that patients with mitochondrial myopathies can benefit from short-term aerobic exercise training. In this study, we compared the responses to short-term aerobic training of patients with mitochondrial myopathies, patients with nonmetabolic myopathies, and sedentary normal subjects. Training consisted of 8 weeks of treadmill exercise at 70% to 85% of estimated maximum heart rate reserve. All groups showed significant improvements in estimated aerobic capacity as well as heart rate and blood lactate at submaximal exercise intensities. The increase in estimated aerobic capacity was greater in the mitochondrial myopathy patients than in the other two groups. Phosphorus magnetic resonance spectroscopy demonstrated increased oxidative capacity of muscle in patients with mitochondrial myopathies in response to this training but not in patients with other, nonmetabolic myopathies or sedentary control subjects. A self-assessed measurement of functional status (SF-36) suggested improved quality of life associated with the training. This study demonstrates that short-term aerobic training at low intensity can benefit patients with nonmetabolic myopathies but to a lesser extent than patients with mitochondrial myopathies.     

Lipid storage myopathies

Summary Various cases of lipid storage myopathies have been described. The biochemical defect could be determined in only some of these cases. The syndromes identified to date are as follows: carnitine deficiency (type I lipid storage myopathy), carnitine-palmityltransferase (CPT) deficiency and pyruvate-decarboxylase deficiency. In the last two diseases the vacuolization in muscle is not marked.The case of a 10 year old carnitine deficient patient with a history of insidious muscle weakness in the proximal limb and neck muscles is presented. The patient was treated with oral carnitine and a medium chain triglyceride diet for 18 months and her clinical status has remained improved. In other lipid storage patients prednisone treatment resulted in improvement.In cases of suspected lipid storage myopathy the following studies are indicated: 1) examination of ketone bodies in serum and urine during fasting, long chain and medium chain triglyceride diets; 2) serum triglyceride and serum carnitine; 3) study on fresh muscle and fibroblasts with labeled substrates, biochemical determination of carnitine and CPT in muscle.This paper was presented at the meeting of the Swiss Neurological Society and the Swiss Society of Muscular Disease in November 1975, Zürich, Switzerland     

Treatment of inflammatory myopathies

The treatment of the immune-mediated inflammatory myopathies remains largely empirical. Corticosteroids are usually effective in polymyositis and dermatomyositis but may need to be combined with methotrexate or azathioprine in some patients. Intravenous immunoglobulin (IVIg) is effective as add-on therapy in some patients not adequately controlled with steroids or immunosuppressive agents, but further controlled trials of IVIg are necessary to define the indications and optimal dose regimens. Cyclophosphamide, cyclosporin, or chlorambucil may be effective in patients with refractory polymyositis or dermatomyositis. Low-dose whole body or lymphoid irradiation is a last option in severely disabled patients resistant to all other treatments. As a small proportion of patients with inclusion body myositis respond to corticosteroid or immunosuppressive therapy, a 3–6-month trial of such therapy is justified in this condition. More specific immunotherapy for these disorders awaits identification of the target antigens and further clarification of the immunopathogenetic mechanisms. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20:651–664, 1997.     

Mitochondrial abnormalities in the myofibrillar myopathies

Myofibrillar myopathies are a genetically diverse group of skeletal muscle disorders, with distinctive muscle histopathology. Causative mutations have been identified in the genes MYOT, LDB3, DES, CRYAB, FLNC, BAG3, DNAJB6, FHL1, PLEC and TTN, which encode proteins which either reside in the Z‐disc or associate with the Z‐disc. Mitochondrial abnormalities have been described in muscle from patients with a myofibrillar myopathy. We reviewed the literature to determine the extent of mitochondrial dysfunction in each of the myofibrillar myopathy subtypes. Abnormal mitochondrial distribution is a frequent finding in each of the subtypes, but a high frequency of COX‐negative or ragged red fibres, a characteristic finding in some of the conventional mitochondrial myopathies, is a rare finding. Few in vitro studies of mitochondrial function have been performed in affected patients.     

Annexin expression in inflammatory myopathies

The pathogenesis of the inflammatory myopathies is still unclear, making their treatment largely empirical. Improved understanding of the molecular mechanisms of inflammatory muscle injury may, however, lead to the development of more specific immunotherapies. To elucidate a possible pathogenic contribution of calcium-binding proteins such as the annexins, we immunohistochemically investigated muscle biopsy specimens from patients with dermatomyositis (10 cases), polymyositis (9 cases), and inclusion-body myositis (4 cases), compared to control cases comprising sarcoid myopathy (3 cases), Duchenne muscular dystrophy (DMD; 4 cases), and normal muscle (3 cases). We found expression of annexins A1, A2, A4, and A6 in the vascular endothelium of all cases. Myofibers expressed annexins A5, A6, and A7 diffusely and weakly in the cytosol, whereas annexins A5 and A7 were also particularly localized to the sarcolemma. In the inflammatory myopathies, in areas of myonecrosis in DMD, and in granulomatous lesions of sarcoid myopathy, reactivity of annexins A1, A2, A4, A5, and A6 was observed in macrophages and T-lymphocytes. Whereas the latter annexins appear to be nonspecific indicators of activation, annexin A1 upregulation may represent endogenous anti-inflammatory mechanisms that merit further investigation.     

Myofibrillar myopathies

Myofibrillar myopathies represent a group of muscular dystrophies with a similar morphologic phenotype. They are characterized by a distinct pathologic pattern of myofibrillar dissolution associated with disintegration of the Z-disk, accumulation of myofibrillar degradation products, and ectopic expression of multiple proteins and sometimes congophilic material. The clinical features of myofibrillar myopathies are more variable. These include progressive muscle weakness, that often involves or begins in distal muscles but limb-girdle or scapuloperoneal distributions can also occur. Cardiomyopathy and peripheral neuropathy are frequent associated features. EMG of the affected muscles reveals myopathic motor unit potentials and abnormal irritability often with myotonic discharges. Rarely, neurogenic motor unit potentials or slow nerve conductions are present. The generic diagnosis of myofibrillar myopathies is based on muscle biopsy findings in frozen sections. To date, all myofibrillar myopathy mutations have been traced to Z-disk-associated proteins, namely, desmin, αB-crystallin, myotilin, ZASP, filamin C and Bag3. However, in the majority of the myofibrillar myopathy patients the disease gene awaits discovery.     

Chemokine-like factor expression in the idiopathic inflammatory myopathies

Objectives –  We evaluated the expression of chemokine-like factor (CKLF) in biopsied muscle fibers in inflammatory myopathies, non-inflammatory myopathies and neurologically diseased controls.
Materials and methods –  We studied the expression of CKLF in 15 polymyositis (PM), five dermatomyositis (DM), 15 non-inflammatory myopathies and nine neurologically diseased patients by immunohistochemistry.
Results –  Chemokine-like factor was mostly expressed in small diameter muscle fibers surrounded by infiltrated lymphocytes of inflammatory myopathies patients. Parts of them were also positive for the staining of the developmental form of myosin heavy chain, a maker of regenerating muscle fibers. Thrombin immunoreactivity was observed in endomysium in PM and perimysium in DM. In vitro differentiation study showed a constitutive expression of CKLF in myoblasts that was abolished in myotubes during differentiation process and was induced again by thrombin. Thrombin regulates CKLF expression through protease-activated receptor-1 in myotubes. Treatment of a protein kinase C inhibitor partially blocked CKLF expression in myoblasts, while it remarkably inhibited that in myotubes.
Conclusion –  Chemokine-like factor expression is differentially regulated in myoblasts and myotubes. Thrombin could be a strong regulator for its expression. As CKLF is immunohistochemically positive in regenerating muscle fibers, we postulate here that CKLF is a useful marker for regenerating muscle fibers in inflammatory myopathies.     

Diagnostic impact of myotonic discharges in myofibrillar myopathies

Introduction: In patients with myofibrillar myopathies (MFM), myotonic discharges have occasionally been detected by needle electromyography (EMG). Nevertheless, this peculiar type of spontaneous repetitive discharge has not attracted special interest in the genetically heterogeneous MFMs. Methods: EMG features were analyzed in 6 patients with genetically confirmed MFM (n = 1 MYOT, n = 1 DES, n = 2 ZASP, n = 2 FLNC). Results: Fibrillation potentials, positive sharp waves, and myotonic discharges were found in all 6 patients, and complex repetitive discharges were found in 5. Myotonic discharges were detected in approximately 50% of the analyzed muscles independent of the site, including distal (3/6), proximal limb (4/6), and paravertebral muscles (3/6). Clinical myotonia could not be elicited in any patient. Conclusions: Myotonic discharges appear to be part of the electrodiagnostic characteristics of myofibrillar myopathy. Along with other appropriate clinical and histological findings, the presence of myotonic discharges supports the diagnosis of myofibrillar myopathy. Muscle Nerve 47: 845–848, 2013     

Myopathology in congenital myopathies

Congenital myopathies are clinically and genetically a heterogeneous group of early onset neuromuscular disorders, characterized by hypotonia and muscle weakness. Clinical severity and age of onset are variable. Many patients are severely affected at birth while others have a milder, moderately progressive or nonprogressive phenotype. Respiratory weakness is a major clinical aspect that requires regular monitoring. Causative mutations in several genes have been identified that are inherited in a dominant, recessive or X‐linked manner, or arise de novo. Muscle biopsies show characteristic pathological features such as nemaline rods/bodies, cores, central nuclei or caps. Small type 1 fibres expressing slow myosin are a common feature and may sometimes be the only abnormality. Small cores (minicores) devoid of mitochondria and areas showing variable myofibrillar disruption occur in several neuromuscular disorders including several forms of congenital myopathy. Muscle biopsies can also show more than one structural defect. There is considerable clinical, pathological and genetic overlap with mutations in one gene resulting in more than one pathological feature, and the same pathological feature being associated with defects in more than one gene. Increasing application of whole exome sequencing is broadening the clinical and pathological spectra in congenital myopathies, but pathology still has a role in clarifying the pathogenicity of gene variants as well as directing molecular analysis.     

Iatrogenic and toxic myopathies

There has been increasing awareness of the adverse effects of therapeutic agents and exogenous toxins on the structure and function of muscle. The resulting clinical syndrome varies from one characterized by muscle pain to profound myalgia, paralysis, and myoglobinuria. Because toxic myopathies are potentially reversible, their prompt recognition may reduce their damaging effects or prevent a fatal outcome. Interest in the toxic myopathies, however, derives not only from their clinical importance but also from the fact that they serve as useful experimental models in muscle research. Morphological and biochemical studies have increased our understanding of the basic cellular mechanisms of myotoxicity. Toxins may produce, for instance, necrotizing, lysosomal-related, inflammatory, anti-microtubular, mitochondrial, hypokalemia-related, or protein synthesis-related muscle damage.     

炎症性肌病247例临床与病理研究

目的探讨多发性肌炎（PM）、间质性肌炎（IM）与神经肌炎（NM）的临床特点及神经肌肉活检的诊断价值。方法回顾分析247例炎症性肌病的临床表现及神经肌肉活检结果。结果3组临床表现相似,为近端肌无力、肌痛等;均有不同程度的肌酶增高,但PM组增高明显;IM和NM具有PM的病理改变,但炎性程度不及PM,又各有其特异性,IM组为炎性细胞浸润间质,NM组神经活检多有髓鞘脱失、炎性细胞浸润。结论PM、IM、NM炎性肌病的临床表现相似,诊断困难,需结合神经肌肉活检等辅助检查才能作出正确的诊断。     

Expression of transglutaminase 2 does not differentiate focal myositis from generalized inflammatory myopathies

Objectives –  Idiopathic inflammatory myopathies (IIM), including dermatomyositis (DM), polymyositis (PM), sporadic inclusion-body myositis (s-IBM) and focal myositis (FM) are a heterogeneous group of autoimmune disorders of skeletal muscle. An increased transglutaminase 2 (TG2) expression has been found in DM, PM and s-IBM. The aim of our study was to investigate TG2 expression in FM in comparison with other IIM.
Materials and methods –  We re-examined tissue material we have gathered in the course of our previous studies on IIM, investigating muscle expression of TG2 in patients with FM in comparison with DM, PM and s-IBM using immunocytochemistry and real-time RT-PCR.
Results –  Immunocytochemistry revealed an increased TG2 signal in endomysial vessels, in atrophic and degenerating/regenerating muscle fibres in PM, DM, s-IBM and FM; in s-IBM, some vacuoles were immunostained too. Real-time RT-PCR study confirmed a significantly increased expression of TG2 in all IIM muscles examined.
Conclusions –  Our study demonstrates the presence of TG2 in FM muscles. The study suggests that TG2 expression does not represent a distinctive marker to differentiate FM from generalized IIM. TG2 over-expression in inflamed skeletal muscle does not seem have a pathogenetic role in such a disease, but it could represent a way to contain the inflammatory process.     

长期糖皮质激素治疗对特发性炎性肌病Lp(a)和hs-CRP水平的影响

目的通过检测特发性炎性肌病(IIM)患者糖皮质激素(简称"激素")治疗前、后不同时期血清脂蛋白(a)〔Lp(a)〕、超敏C反应蛋白(hs-CRP)水平变化,观察激素对IIM患者体内炎性状态的影响。方法选择确诊IIM患者25例(肌炎组),分别在泼尼松片治疗前及治疗后第3、6、9、12个月采用免疫散色比浊法和免疫透射比浊法检测其血清Lp(a)和hs-CRP水平,同时检测血总胆固醇(CHO)、甘油三酯(TG)、高密度脂蛋白胆固醇(HDL)、低密度脂蛋白胆固醇(LDL-C)、尿酸、同型半胱氨酸(HCY)水平。另选择15名作者医院门诊体检的健康人员检测其上述指标,作为健康对照,进行比较分析。结果肌炎组治疗前Lp(a)、hs-CRP、CHO、LDL-C、HDL、血尿酸、HCY水平与对照组比较差异均无统计学意义(均P0.05)。肌炎组患者治疗后第3、6、9、12个月Lp(a)、hs-CRP水平均较治疗前及对照组明显升高(均P0.05),治疗后第6个月与第9、12个月比较无明显差异(P0.05)。肌炎组治疗后各观察月CHO、LDL-C、HDL、血尿酸、HCY水平及治疗后第3个月TG水平与治疗前及对照组比较差异无统计学意义(均P0.05);TG在治疗后第6、9、12月水平较对照组、治疗前及治疗后第3月时高(P0.05)。结论长期激素治疗的IIM患者可出现血清Lp(a)、hs-CRP水平升高。     

Seasonal occurrence of relapses in inflammatory myopathies: a preliminary study

The seasonal occurrence of relapses was analysed retrospectively in a group of 53 patients with treated dermatomyositis (DM) or polymyositis (PM). In DM, the incidence of both myositic and cutaneous relapses was highest in summer whereas in the PM group relapses was more evenly distributed throughout the seasons but lowest in summer. The present findings suggest that environmental factors such as intercurrent infections and light exposure may be involved in reactivating the disease process and causing relapses in DM but less so in PM. Further prospective studies are needed to assess the role of environmental factors in the initiation and reactivation of the inflammatory myopathies. Received: 12 May 2001, Received in revised form: 23 August 2001, Accepted: 27 August 2001