Nemaline Rods Research Articles

Ca 2+ dysregulation in Ryr1 I4895T/wt mice causes congenital myopathy with progressive formation of minicores, cores, and nemaline rods

Ryr1(I4895T/wt) (IT/+) mice express a knockin mutation corresponding to the human I4898T EC-uncoupling mutation in the type 1 ryanodine receptor/Ca(2+) release channel (RyR1), which causes a severe form of central core disease (CCD). IT/+ mice exhibit a slowly progressive congenital myopathy, with neonatal respiratory stress, skeletal muscle weakness, impaired mobility, dorsal kyphosis, and hind limb paralysis. Lesions observed in myofibers from diseased mice undergo age-dependent transformation from minicores to cores and nemaline rods. Early ultrastructural abnormalities include sarcomeric misalignment, Z-line streaming, focal loss of cross-striations, and myofibrillar splitting and intermingling that may arise from defective myofibrillogenesis. However, manifestation of the disease phenotype is highly variable on a Sv129 genomic background. Quantitative RT-PCR shows an equimolar ratio of WT and mutant Ryr1 transcripts within IT/+ myofibers and total RyR1 protein expression levels are normal. We propose a unifying theory in which the cause of core formation lies in functional heterogeneity among RyR1 tetramers. Random combinations of normal and either leaky or EC-uncoupled RyR subunits would lead to spatial differences in Ca(2+) transients; the resulting heterogeneity of contraction among myofibrils would lead to focal, irreversible tearing and shearing, which would, over time, enlarge to form minicores, cores, and nemaline rods. The IT/+ mouse line is proposed to be a valid model of RyR1-related congenital myopathy, offering high potential for elucidation of the pathogenesis of skeletal muscle disorders arising from impaired EC coupling.

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.

Core Myopathies and Risk of Malignant Hyperthermia

In this article, we analyze myopathies with cores, for which an association to malignant hyperthermia (MH) has been suggested. We discuss the clinical features, the underlying genetic defects, subsequent effects on cellular calcium metabolism, and in vitro muscle responses to MH triggers. We describe in detail central core disease, multiminicore disease, and nemaline rod myopathy. We categorize the diseases according to the affected proteins and discuss the risk for MH, which is high or theoretically possible when the calcium-conducting proteins are affected.

V05 Poster location 005 A novel SLC2A1 mutation causing paroxysmal exercise-induced dyskinesia and childhood absence seizures

apnoea in the post-operative (inguinal hernia repair) period needing ventilation. Recurrent episodes of apnoea, bradycardia, and sometimes asystole needing cardio-pulmonary resuscitation (CPR) ensued. Initially these episodes were thought to be triggered by the act of opening his bowels with contraction of abdominal wall muscles along with intermittent yellowishgreen discolouration of scrotum but no clear Harlequin colour change was seen (video). This would progress to apnoea, bradycardia and eventually asystole needing resuscitation from bag and face mask ventilation to full CPR. He had very stiff and hypertrophied abdominal muscles, increased tone and arthrogryposis of limbs. He did not have an exaggerated startle. Deep tendon reflexes appeared myotonic (video). Hyperekplexia, paroxysmal episodic pain disorder (PEPD), neuromyotonia were considered in the differential and tested for. EMG was normal. He had normal MRI (brain and cervical spine) and EEG. Results of genetic testing for hyperekplexia and PEPD were normal along with other neurometabolic investigations. The muscle biopsy revealed nemaline rods. A novel mutation of ACTA1 gene, heterozygous c.984G>C; p. Lys328Asn sequence variant was detected in exon 5. Despite various pharmacological and supportive interventions he died aged 9 months. This is a genetically and phenotypically heterogeneous rare form of congenital myopathy, which is characterized by slow or non-progressive muscle weakness and pathognomonic abnormal rod-like structures within the affected muscle fibers. Our case adds to the protean presentation of nemaline myopathy being only the second case in the literature with clinical features of stiffness rather than weakness.

G.P.12.09 Actin myopathy with myofibrillar dysgenesis and abnormal ossification

Skeletal muscle α-actin (ACTA1) gene mutations result in a myopathy with histopathological characteristics that include cytoplasmic nemaline rods, intranuclear rods and abnormal actin aggregates. The severity of muscle weakness and cardiomyopathy show clinical variability with onset age from neonatal period to adulthood, but extramuscular manifestations have been rarely described in patients with actinopathy.

Longitudinal study of the effects of chronic hypothyroidism on skeletal muscle in dogs

To study the effects of experimentally induced hypothyroidism on skeletal muscle and characterize any observed myopathic abnormalities in dogs. 9 female, adult mixed-breed dogs; 6 with hypothyroidism induced with irradiation with 131 iodine and 3 untreated control dogs. Clinical examinations were performed monthly. Electromyographic examinations; measurement of plasma creatine kinase, alanine aminotransferase, aspartate aminotransferase, lactate, and lactate dehydrogenase isoenzyme activities; and skeletal muscle morphologic-morphometric examinations were performed prior to and every 6 months for 18 months after induction of hypothyroidism. Baseline, 6-month, and 18-month assessments of plasma, urine, and skeletal muscle carnitine concentrations were also performed. Hypothyroid dogs developed electromyographic and morphologic evidence of myopathy by 6 months after treatment, which persisted throughout the study, although these changes were subclinical at all times. Hypothyroid myopathy was associated with significant increases in plasma creatine kinase, aspartate aminotransferase, and lactate dehydrogenase 5 isoenzyme activities and was characterized by nemaline rod inclusions, substantial and progressive predominance of type I myofibers, decrease in mean type II fiber area, subsarcolemmal accumulations of abnormal mitochondria, and myofiber degeneration. Chronic hypothyroidism was associated with substantial depletion in skeletal muscle free carnitine. Chronic, experimentally induced hypothyroidism resulted in substantial but subclinical phenotypic myopathic changes indicative of altered muscle energy metabolism and depletion of skeletal muscle carnitine. These abnormalities may contribute to nonspecific clinical signs, such as lethargy and exercise intolerance, often reported in hypothyroid dogs.

Severe nemaline myopathy associated with consecutive mutations E74D and H75Y on a single ACTA1 allele

Nemaline myopathy is among the most common congenital myopathies. We describe for the first time a novel double de novo mutation in two adjacent codons resulting in two amino acid changes E74D and H75Y in the ACTA1 gene. The hypotonic male infant was the first son of healthy unrelated parents with no family history of neuromuscular disorders. Pregnancy was complicated: decreased fetal movements were noted on the 25th week of gestation, premature labour pains were present from the 29th week onwards and because of breech presentation a Caesarian section was carried out in the 39th week. The patient presented with multiple congenital fractures and joint contractures. He was dependent on ventilatory support until his death at 2 months. Muscle biopsy revealed severely atrophic and rounded muscle fibers with considerable variation in diameter and pronounced disorganization of the myofibers. Electron microscopy indicated a distinct disturbance of the myofibrillar architecture and nemaline rods. In view of previously described cases carrying different single missense mutations of the amino acid residues E74 or H75, we suggest that the particular genotype E74D/H75Y is compatible with the severity of the patient’s phenotype. The possibility of germ cell mosaicism should be taken into account in genetic counseling.

TPM3 mutation in one of the original cases of cap disease

Cap disease is a rare congenital skeletal muscle disorder characterized by the presence of cap-like structures which are well demarcated and peripherally located under the sarcolemma and show abnormal accumulation of sarcomeric proteins.1,2 Clinical features are early onset of hypotonia and nonprogressive or slowly progressive muscle weakness. Respiratory problems are common. Five dominant mutations have been reported in association with cap disease, all in the β-tropomyosin (βTm) gene ( TPM2 ).3-5 We report a mutation in the αTmslow (γTm) gene ( TPM3 ) in a patient with cap disease, supporting the concept that cap disease is genetically heterogeneous and closely related to nemaline myopathy.4 ### Case report. This 38-year-old woman was first described in 2002 (patient K.D.).2 There was no family history of neuromuscular disorder. She was born at term after an uncomplicated pregnancy, labor, and delivery. She had somewhat delayed motor milestones and at age 5 years mild motor difficulties were noted. She could not keep up with her peers and could not run. At age 18 years, a muscle biopsy was performed and the diagnosis of congenital myopathy (cap disease) was established (figure). Nemaline rods were not identified. EMG showed a myopathic pattern. She was admitted to hospital with pneumonia when she was 21 years old …

α-Skeletal muscle actin nemaline myopathy mutants cause cell death in cultured muscle cells

Nemaline myopathy is a neuromuscular disorder, characterized by muscle weakness and hypotonia and is, in 20% of the cases, caused by mutations in the gene encoding α-skeletal muscle actin, ACTA1. It is a heterogeneous disease with various clinical phenotypes and severities. In patients the ultrastructure of muscle cells is often disturbed by nemaline rods and it is thought this is the cause for muscle weakness. To search for possible defects during muscle cell differentiation we expressed α-actin mutants in myoblasts and allowed these cells to differentiate into myotubes. Surprisingly, we observed two striking new phenotypes in differentiating myoblasts: rounding up of cells and bleb formation, two features reminiscent of apoptosis. Indeed expression of these mutants induced cell death with apoptotic features in muscle cell culture, using AIF and endonuclease G, in a caspase-independent but calpain-dependent pathway. This is the first report on a common cellular defect induced by NM causing actin mutants, independent of their biochemical phenotypes or rod and aggregate formation capacity. These data suggest that lack of type II fibers or atrophy observed in nemaline myopathy patients may be also due to an increased number of dying muscle cells.

Idiopathic adult‐onset nemaline myopathy presenting with isolated respiratory failure

Idiopathic adult-onset nemaline myopathy is a rare condition of unknown etiology that usually presents with proximal weakness. This case study reports a 60-year-old woman who presented with isolated type 2 respiratory failure secondary to bilateral hemidiaphragm weakness. A left vastus medialis muscle biopsy examined under light microscopy revealed appearances typical of nemaline myopathy. Electron microscopy confirmed the presence of nemaline rods in most muscle fibers, thus establishing idiopathic adult-onset nemaline myopathy as the cause of her respiratory failure. Our patient's presentation highlights the importance of considering neuromuscular weakness as a cause of respiratory failure. Unless appropriate tests are performed-including a muscle biopsy, if indicated-specific neuromuscular diseases are easily missed. This can lead to inappropriate counseling and treatment.

Phenotypes induced by NM causing α-skeletal muscle actin mutants in fibroblasts, Sol 8 myoblasts and myotubes

BackgroundNemaline myopathy is a neuromuscular disorder characterized by the presence of nemaline bodies in patient muscles. 20% of the cases are associated with α-skeletal muscle actin mutations. We previously showed that actin mutations can cause four different biochemical phenotypes and that expression of NM associated actin mutants in fibroblasts, myoblasts and myotubes induces a range of cellular defects.FindingsWe conducted the same biochemical experiments for twelve new actin mutants associated with nemaline myopathy. We observed folding and polymerization defects. Immunostainings of these and eight other mutants in transfected cells revealed typical cellular defects such as nemaline rods or aggregates, decreased incorporation in F-actin structures, membrane blebbing, the formation of thickened actin fibres and cell membrane blebbing in myotubes.ConclusionOur results confirm that NM associated α-actin mutations induce a range of defects at the biochemical level as well as in cultured fibroblasts and muscle cells.

Pathological defects in congenital myopathies

Congenital myopathies are a molecularly, pathologically and clinically heterogenous group of disorders defined by hypotonia and muscle weakness, that usually present at birth or early childhood, in association with a characteristic morphological defect. The most common morphological defects are nemaline rods, cores of varying size, central nuclei, and type I fibre hypotrophy, with or without an additional abnormality. The defective genes responsible for many of the congenital myopathies are known, but there is considerable clinico-pathological overlap. In particular, defects in more than one gene are associated with the presence of the same pathological feature, while defects in the same gene can result in more than one pathological feature. Understanding the complexities of these spectra is paramount to the elucidation of pathogenesis, and to the development of therapies.

G.P.13.01 A family with Trismuspseudocamptodactaly and nemaline rods on muscle biopsy. Expanding the nemaline myopathy phenotype ?

We describe a family of three generations with inability to open the mouth completely, pseudocamptodactyly and proximal muscle weakness. Short finger flexors contractions resulted in camptodactyly when the wrist was dorsiflexed. Mouth opening was limited and resulted in difficulties in mastication. In addition the inability to open the mouth made any incubations potentially very hazardous. We undertook a Myosin Heavy Chain 8 (MYH8) mutation analysis to ascertain if a previously described arg674-to-gln mutation in the MYH8 gene was present. We also screened the family history for Dutch ancestry which was negative. Muscle biopsy on the mother and daughter revealed nemaline rods in both samples. The grandmother who had all the clinical features and proximal muscle weakness did not have a muscle biopsy. A review of the literature revealed that nemaline rods have not been previously described in this condition. We speculate on the potential mechanisms.

A “nema” of hope in the treatment of late-onset nemaline myopathy

Sporadic, late-onset nemaline myopathy (SLONM) presents with subacute onset of proximal > distal muscle weakness in adults above the age of 40.1,2 It can cause head drop, dysphagia, or respiratory insufficiency, leading to severe disability or death. The diagnosis is confirmed with the muscle biopsy that shows abundance of nemaline (from the Greek word nema = thread) rod bodies representing Z-disc disorganization products which immunoreact with α-actinin and myotilin.1 In contrast to heritable nemaline myopathies, the most common nondystrophic congenital myopathies of childhood caused by mutations in the α-skeletal actin, nebulin, or troponin genes,3 the cause of SLONM is unknown. Because at least 50% of SLONM cases are associated with monoclonal gammopathy,1,2,4 and some of them occur in the early stages of HIV infection during the period of immunocompetence,5 an immune dysregulation has been suspected for at least some of them.1,2,4 A causal relationship, however, between the gammopathy and …

Histopathologic Progression and a Novel Mutation in a Child With Nemaline Myopathy

Nemaline myopathy is a clinically heterogeneous congenital myopathy caused by mutations in at least 6 genes related to thin filaments. Histologically, they show a characteristic if not homogeneous picture of nemaline rods, essential for the diagnosis. However, little is known regarding the development and progression of muscle histopathologic changes in nemaline myopathy. Results of muscle biopsies at 7 weeks of age and at 15 months of age from a child with nemaline myopathy due to a novel mutation in the ACTA1 gene are presented. The findings of the biopsies, separated by 13 months, demonstrate progression from vague cytoplasmic bodies in the first biopsy to typical nemaline rods in the second biopsy.

Identification of a founder mutation in TPM3 in nemaline myopathy patients of Turkish origin

To date, six genes are known to cause nemaline (rod) myopathy (NM), a rare congenital neuromuscular disorder. In an attempt to find a seventh gene, we performed linkage and subsequent sequence analyses in 12 Turkish families with recessive NM. We found homozygosity in two of the families at 1q12-21.2, a region encompassing the gamma-tropomyosin gene (TPM3) encoding slow skeletal muscle alpha-tropomyosin, a known NM gene. Sequencing revealed homozygous deletion of the first nucleotide of the last exon, c.913delA of TPM3 in both families. The mutation removes the last nucleotide before the stop codon, causing a frameshift and readthrough across the termination signal. The encoded alphaTm(slow) protein is predicted to be 73 amino acids longer than normal, and the extension to the protein is hypothesised to be unable to form a coiled coil. The resulting tropomyosin protein may therefore be non-functional. The affected children in both families were homozygous for the mutation, while the healthy parents were mutation carriers. Both of the patients in Family 1 had the severe form of NM, and also an unusual chest deformity. The affected children in Family 2 had the intermediate form of NM. Muscle biopsies showed type 1 (slow) fibres to be markedly smaller than type 2 (fast) fibres. Previously, there had been five reports, only, of NM caused by mutations in TPM3. The mutation reported here is the first deletion to be identified in TPM3, and it is likely to be a founder mutation in the Turkish population.

Morphologic Assessment of Muscle Biopsy Abnormalities in Patients with Congenital Fiber Type Disproportion and Tropomyosin 3 Mutation

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 I 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. Using genomic PCR and DNA sequencing, 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 5 out of 12 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 TPM3 mutation all displayed marked disproportion of fiber size, without type I 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.

Congenital myopathies: A clinicopathological study of 25 cases

Congenital myopathies are rare. Through this article, the authors want to present a clinicopathological analysis of 25 new cases. The clinical data of patients who were diagnosed with congenital myopathy between 2001 and 2006 was retrieved. Muscle biopsies were processed for H&E staining, enzyme histochemistry, and immunohistochemistry. Biopsies were also processed for ultrastructural analysis. During a period of 6 years, 1.12% of the muscle biopsies were diagnosed as congenital myopathies. The most common congenital myopathy was central core disease followed by nemaline rod myopathy and multi-mini core disease. Clinically, they have variable features. The final diagnosis was made with the help of enzyme histochemistry and ultrastructural features. This study emphasizes the importance of enzyme histochemistry and electron microscopic examination in the diagnosis of congenital myopathies especially in the absence of genetic studies.

C.P.1.07 Exercise intolerance as a presentation of adult onset nemaline (rod) myopathy

C.P.1.07 Exercise intolerance as a presentation of adult onset nemaline (rod) myopathy

Congenital Myopathy With Nemaline Rods and Cap Structures Caused by a Mutation in the β-Tropomyosin Gene (TPM2)

To describe the clinical, morphologic, and genetic findings in a family in which one woman had nemaline myopathy, whereas her daughter showed features of cap disease. A 66-year-old woman and her 35-year-old daughter had congenital, slowly progressive muscle weakness. They had weakness in both proximal and distal muscles and facial diplegia with bilateral ptosis, a long narrow face, a high arched palate, and micrognathia. Muscle biopsy specimens in the mother at age 57 years had shown nemaline myopathy, whereas a biopsy specimen at age 32 years had demonstrated no rods. Muscle biopsy specimens in the daughter at age 26 years had shown features of cap disease and no apparent nemaline rods. A missense mutation, Glu41Lys, in the beta-tropomyosin gene TPM2 was identified in both patients but was absent in their healthy relatives. The results indicate that mutations in TPM2 may cause nemaline myopathy as well as cap disease with a dominant mode of inheritance. These disorders may thus be phenotypic variants of the same genetic defect.