Cardiac ankyrin repeat protein is preferentially induced in atrophic myofibers of congenital myopathy and spinal muscular atrophy

Cardiac ankyrin repeat protein (CARP), which is structurally characterized by the presence of four ankyrin repeat motifs in its central region, is believed to be localized in the nucleus and to participate in the regulation of cardiac-specific gene expression in cardiomyocytes. However, we recently found that CARP was induced in skeletal muscle by denervation, leading us to speculate that CARP may be induced under some pathological conditions. In the present study, we immunohistochemically analyzed the expression of CARP in 11 cases of spinal muscular atrophy (SMA) and 14 cases of congenital myopathy. In SMA, CARP was expressed selectively in severely atrophic myofibers, suggesting that CARP expression may reflect the status of muscle atrophy. Furthermore, in the congenital myopathies, the expression patterns of CARP were distinct among the subtypes, which included nemaline myopathy, myotubular myopathy, central core disease, and congenital fiber type disproportion. Although CARP was preferentially expressed in severely damaged myofibers in nemaline myopathy, it was not detected in central core disease. These findings suggest that immunohistochemical evaluation of CARP may be helpful in the diagnosis of SMA and the congenital myopathies.     

Congenital myopathies

Most congenital myopathies have been defined on account of the morphological findings in enzyme histochemical preparations. In effect, the diagnosis of this group of diseases continues to be made on the histological pattern of muscle biopsies. However, progress has been made in elucidating the molecular genetic background of several of the congenital myopathies. In this updated review we address those congenital myopathies for which gene defects and mutant proteins have been found (central core disease, nemaline myopathies, desminopathy, actinopathy, certain vacuolar myopathies, and myotubular myopathy) and the other disease with central nuclei (centronuclear myopathy).     

Autosomal dominant centronuclear myopathy with unique clinical presentations

Centronuclear myopathies are clinically and genetically heterogenous diseases with common histological findings, namely, centrally located nuclei in muscle fibers with a predominance and hypotrophy of type 1 fibers. We describe two cases from one family with autosomal dominant centronuclear myopathy with unusual clinical features that had initially suggested distal myopathy. Clinically, the patients presented with muscle weakness and atrophy localized mainly to the posterior compartment of the distal lower extremities. Magnetic resonance imaging revealed predominant atrophy and fatty changes of bilateral gastrocnemius and soleus muscles. This report demonstrates the expanding clinical heterogeneity of autosomal dominant centronuclear myopathy.     

Muscle diseases in Singapore

This study aims to establish the pattern of muscle diseases in Singapore. Two hundred consecutive muscle biopsies collected prospectively over a period of 7 yr (1978-1984) were studied using light microscopy, histochemistry and electron microscopy. Muscle diseases were not uncommon. There was no racial predilection. The common muscle diseases were polymyositis, spinal muscular atrophies and muscular dystrophies. Less common ones included congenital myopathies and storage diseases due to disorders of glycogen and lipid metabolism. Other muscle diseases were uncommon. Polymyositis was the commonest muscular disorder in adults and spinal muscular atrophy in childhood. This finding is encouraging as polymyositis is a treatable condition. The common occurrence of spinal muscular atrophies in this country was not fully appreciated. They were often misdiagnosed clinically as muscular dystrophies. It is hoped that this finding will result in greater awareness of this condition which is necessary for proper genetic counselling and management.     

Not Antley-Bixler syndrome

A single report of brothers born to first-cousin parents with a form of acute spinal muscular atrophy (SMA) and congenital fractures suggested that this combination represented a distinct form of autosomal recessive SMA. We describe a boy with hypotonia and congenital fractures whose sural nerve and muscle biopsies were consistent with a form of spinal muscular atrophy. Molecular studies identified no abnormality of the SMN(T) gene on chromosome 5. This case serves to validate the suggestion of a distinct and rare form of spinal muscular atrophy while not excluding possible X-linked inheritance.     

Intramuscular hematopoiesis in hypotonic infants with type 1 muscle fiber dysmaturation

Three term infants had severe hypotonia, a maturation defect of type 1 muscle fibers, and extramedullary hematopoiesis (EMH) in quadriceps muscle specimens obtained within one month of birth. Although predominantly myelopoietic, signs of inflammatory myopathy were absent. One patient had congenital myopathy with maturation arrest of type 1 fibers, another had transient maturation delay of type 1 fibers, and the third patient was subsequently classified as having spinomuscular atrophy. Extramedullary hematopoiesis was demonstrated in normal muscle obtained from young fetuses, but not in muscle obtained at autopsy from infants representing the third trimester and first postnatal month, or in muscle biopsy specimens from 15 other hypotonic infants with type 1 fiber size disproportion. We conclude that EMH in muscle of hypotonic infants is an abnormal persistence of a fetal state that is associated with delayed muscle maturation with diverse origins. Extramedullary hematopoiesis in muscle may indicate hypoxia, but signs of perinatal asphyxia in these babies were inconclusive. Low blood flow due to inactivity or an unidentified product of immature muscle may promote intramuscular EMH, but there is no evidence to suggest that myelopoiesis is injurious to muscle fibers. Intramuscular EMH should be distinguished from inflammation.     

Spinal muscular atrophy variant with congenital fractures

A single report of brothers born to first-cousin parents with a form of acute spinal muscular atrophy (SMA) and congenital fractures suggested that this combination represented a distinct form of autosomal recessive SMA. We describe a boy with hypotonia and congenital fractures whose sural nerve and muscle biopsies were consistent with a form of spinal muscular atrophy. Molecular studies identified no abnormality of the SMN^T gene on chromosome 5. This case serves to validate the suggestion of a distinct and rare form of spinal muscular atrophy while not excluding possible X-linked inheritance. Am. J. Med. Genet. 87:65–68, 1999. © 1999 Wiley-Liss, Inc.     

Recessive RYR1 mutations in a patient with severe congenital nemaline myopathy with ophthalomoplegia identified through massively parallel sequencing

Nemaline myopathy (NM) is a group of congenital myopathies, characterized by the presence of distinct rod-like inclusions "nemaline bodies" in the sarcoplasm of skeletal muscle fibers. To date, ACTA1, NEB, TPM3, TPM2, TNNT1, and CFL2 have been found to cause NM. We have identified recessive RYR1 mutations in a patient with severe congenital NM, through high-throughput screening of congenital myopathy/muscular dystrophy-related genes using massively parallel sequencing with target gene capture. The patient manifested fetal akinesia, neonatal severe hypotonia with muscle weakness, respiratory insufficiency, swallowing disturbance, and ophthalomoplegia. Skeletal muscle histology demonstrated nemaline bodies and small type 1 fibers, but without central cores or minicores. Congenital myopathies, a molecularly, histopathologically, and clinically heterogeneous group of disorders are considered to be a good candidate for massively parallel sequencing.     

Mutations of tropomyosin 3 (TPM3) are common and associated with type 1 myofiber hypotrophy in congenital fiber type disproportion

Congenital fiber type disproportion (CFTD) is a rare congenital myopathy characterized by hypotonia and generalized muscle weakness. Pathologic diagnosis of CFTD is based on the presence of type 1 fiber hypotrophy of at least 12% in the absence of other notable pathological findings. Mutations of the ACTA1 and SEPN1 genes have been identified in a small percentage of CFTD cases. The muscle tropomyosin 3 gene, TPM3, is mutated in rare cases of nemaline myopathy that typically exhibit type 1 fiber hypotrophy with nemaline rods, and recently mutations in the TPM3 gene were also found to cause CFTD. We screened the TPM3 gene in patients with a clinical diagnosis of CFTD, nemaline myopathy, and with undefined congenital myopathies. Mutations in TPM3 were identified in 6 out of 13 patients with CFTD, as well as in one case of nemaline myopathy. Review of muscle biopsies from patients with diagnoses of CFTD revealed that patients with a TPM3 mutation all displayed marked disproportion of fiber size, without type 1 fiber predominance. Several mutation‐negative cases exhibited other abnormalities, such as central nuclei and central cores. These results support the utility of the CFTD diagnosis in directing the course of genetic testing. Hum Mutat 30:1–8, 2009. © 2009 Wiley‐Liss, Inc.     

Diagnostic yield associated with multiple simultaneous skeletal muscle biopsies

Certain skeletal muscle disorders, such as inflammatory myopathies, may show regional variability, prompting consideration of simultaneous biopsy of more than 1 muscle to increase the likelihood of diagnosis. There are few data in the literature to support this approach. This study is a retrospective 8-year review of 99 cases (52 men; mean age, 61.8 years) who had multiple muscles biopsied simultaneously. The most common clinical symptoms prompting biopsy included weakness in 83 cases and myalgia in 15. The most common diagnoses were as follows: neurogenic atrophy, 48; inflammatory myopathy, excluding inclusion body myositis, 29; and type II muscle fiber atrophy, 24. Diagnoses were the same in both biopsied muscles in 54 cases (55%). In 17 cases, a diagnosis was made from only 1 biopsy. Of 29 inflammatory myopathies and vasculitis (excluding inclusion body myositis), a diagnosis could be made from only 1 of the 2 biopsies in 10 cases (34%). In a significant subset of cases, a potentially treatable inflammatory myopathic condition might have been missed if only 1 site had been biopsied, justifying biopsy of 2 sites in suspected cases of inflammatory myopathy.     

Central nuclear counts in muscle fibres before and during treatment in hypothyroid myopathy

Serial percutaneous needle muscle biopsies of vastus lateralis were studied in 10 patients who had varying degrees of hypothyroid myopathy. The biopsies were taken before and during treatment with l-thyroxine. Before treatment the most severely clinically affected patients showed type II muscle fibre atrophy and loss, together with increased central nuclear counts preferentially affecting the type II muscle fibre. Both the type II muscle fibre atrophy and loss and the increased central nuclear counts tended to return towards normal values during treatment with l-thyroxine. The severity of myopathic symptoms before and during treatment correlated with the biochemical evidence of hypothyroidism, a type II fibre atrophy, and increased central nuclear counts. The severity of myopathic signs before and during treatment was correlated with both a type II fibre atrophy and loss and increased central nuclear counts. There was no evidence that the myopathic signs before and during treatment were related to the biochemical parameters of hypothyroidism, except the level of thyroid stimulating hormone.It is suggested that sequential studies of muscle fibre percentages, diameters, and central nuclear counts may provide an additional method of assessing the response to treatment in hypothyroid and possibly other types of myopathy. When increased central nuclear counts are confined to a specific muscle fibre type, this may suggest a hitherto unsuspected specificity of muscle fibre damage.     

Origin and significance of small muscle fibres in neuromuscular disease

Summary Small muscle fibres, defined as those of less than 40 µm diameter in the male and 30 m in the female were encountered in muscle biopsies of patients with spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS), polymyositis (PM) and myopathy/dystrophy. Excessive reactivity with NADH-TR in small fibres did not discriminate between neurogenic and myopathic disorders. Quantification of perifascicular atrophic fibres, the number of nuclei in atrophic fibres, or the presence of isolated or grouped small fibres without histochemical kinship to their surrounding fibres did not aid recognition of the disease process in the groups studied. Small fibres which reacted strongly both with NADH-TR and ATPase at pH 9.4 (Type 3 fibres) constituted 38% of small fibres in the biopsies of SMA; 25% in ALS; but only 1% and 2.7% in PM and myopathy/dystrophy respectively. Thus, the presence of small Type 3 fibres in muscle biopsies may be a useful marker for neurogenic disorders in adults.     

Mitochondrial abnormalities and ocular myopathies with downward-spreading evolution. Apropos of 2 new cases]

Two cases, one being probably familial, of ocular myopathy are reported. In both the onset was in childhood by ptosis of the eyelids and the course lasted more than 20 years. The patients (32 and 49 years) presented involvement of the ocular muscles as well as of the facial, pharyngolaryngeal, neck and limb muscles. There was, in both cases, marked body weight loss which could not be explained by the muscular atrophy alone, and a thyroid nodule which was not accompanied by evident change in thyroid function. Muscle biopsy studies were carried out : electron microscopy showed in both cases aggregates of mitochondria exhibiting various changes ; in one case histochemistry demonstrated that these changes were confined to type 1 muscle fibres. These cases of descending ocular myopathy can be included therefore in the group of the smaller than myopathies with abnormal mitochondria greater than.     

Distal infantile spinal muscular atrophy associated with paralysis of the diaphragm: a variant of infantile spinal muscular atrophy

We report the clinical, electrophysiological, and morphological observations of five infants with an unusual form of spinal muscular atrophy (SMA). In these infants muscular weakness and atrophy were initially restricted to the distal limbs and this pattern was associated with paralysis of the diaphragm. The difference between the clinical manifestations of this syndrome and the classical form of infantile spinal muscular atrophy (SMA type 1) as well as other congenital hereditary neuropathies is discussed.     

Progressive spinal amyotrophy type I or Werdnig-Hoffman disease. Apropos of 5 cases in Dakar (Senegal)

Type I spinal muscular atrophy or Werdnig-Hoffman disease is rarely described in black populations. We report five such cases diagnosed in a paediatric outpatient clinic in Dakar. We conducted a retrospective study relating to patients examined for hypotonia progressing since birth for whom the electromyogram had made it possible to confirm an involvement of the peripheral nerve without nerve conduction anomaly. Mean age of diagnosis was 12.3 +/- 7.6 months. Respiratory distress was noted for 2 patients. A family background of similar symptomatology was found in 1 case and consanguinity in 2 cases. Only 1 case of death occurred whereas the 4 other patients were lost to follow-up. The diagnosis of spinal muscular atrophy must be considered in the presence of any severe hypotonia in infants.     

Neurogene Muskelatrophien und selektive Muskelfasertypenatrophien

Neurogenic muscular atrophy (NMA) is the most frequent diagnosis obtained from reading a muscle biopsy. It is characterized by specific histological changes which distinguish NMA from other important muscle pathologies including the primary myopathies such as the muscular dystrophies as well as the inflammatory muscle disorders. Within the group of denervation atrophies, NMAs due to motor neuron diseases are associated with particular histological patterns. The diagnosis of NMA in muscle biopsies requires special methods, mainly enzyme and immunohistochemistry, but also resin histology and in some cases electron microscopy. Analysis of a combined muscle and sural nerve biopsy provides the opportunity to compare the extent of degeneration in the motor and sensory systems, respectively. Muscle fiber typing by enzyme and immunohistochemistry also leads to the detection of selective type 1 and type 2 muscle fiber atrophies which are relevant in the differential diagnosis of neuromuscular diseases.     

X-linked myotubular myopathy in a family with two infant siblings: a case with MTM1 mutation

X-linked myotubular myopathy (XLMTM) is a rare congenital muscle disorder, caused by mutations in the MTM1 gene. Affected male infants present severe hypotonia, and generalized muscle weakness, and the disorder is most often complicated by respiratory failure. Herein, we describe a family with 2 infants with XLMTM which was diagnosed by gene analysis and muscle biopsy. In both cases, histological findings of muscle showed severely hypoplastic muscle fibers with centrally placed nuclei. From the family gene analysis, the Arg486STOP mutation in the MTM1 gene was confirmed.     

Congenital myopathies: diseases of the actin cytoskeleton

Congenital myopathies are clinical and genetic heterogeneous disorders characterized by skeletal muscle weakness ranging in severity. Three major forms have been identified: actin myopathy, intranuclear rod myopathy, and nemaline myopathy. Nemaline myopathy is the most common of these myopathies and is further subdivided into seven groups according to severity, progressiveness, and age of onset. At present, five genes have been linked to congenital myopathies. These include alpha-actin (ACTA1), alpha- and beta-tropomyosin (TPM3 and TPM2), troponin T (TNNT1), and nebulin (NEB). Their protein products are all components of the thin filament of the sarcomere. The mutations identified within these genes have varying impacts on protein structure and give rise to different forms of congenital myopathies. Greater understanding of muscle formation and cause of disease can be established through the study of the effect of mutations on the functional proteins. However, a major limitation in the understanding of congenital myopathies is the lack of correlation between the degree of sarcomeric disruption and disease severity. Consequently, great difficulty may be encountered when diagnosing patients and predicting the progression of the disorders. There are no existing cures for congenital myopathies, although improvements can be made to both the standard of living and the life expectancy of the patient through various therapies.