Congenital nemaline myopathy with mitochondrial abnormalities. An adult case report]

We report a 42-year-old male suffering from congenital nemaline myopathy accompanied with mitochondrial abnormalities in his muscle biopsy. He had a dysmorphic face with a high-arched and narrow palate and slowly progressive generalized muscle weakness. He was still able to walk with a cane. CT showed symmetrical muscle atrophy and low densities in the thigh muscles, especially in the posterior compartment, and in the soleus muscles. Preferential posterior thigh involvement was unusual in congenital nemaline myopathy. The lumbar quadrate and paravertebral muscles were relatively well preserved; these muscles were reported to be severely involved in adult-onset nemaline myopathy patients. Muscle biopsy findings were consistent with nemaline myopathy; nemaline rods in approximately 10% of fibers, type 1 fiber atrophy, and type 2B fiber deficiency. In addition, ragged-red fibers were scattered and focal cytochrome c oxidase (CCO) deficiency was present. Formazan granules were large on succinate dehydrogenase stain. Many fibers with nemaline rods showed focal CCO deficiency. On electron microscopy, large (megaconial) mitochondria were lined regularly between Z lines. PCR and Southern blot analysis of muscle mitochondrial DNA revealed multiple deletions. It remains to be clarified whether mitochondrial abnormalities are primarily related to nemaline myopathy or secondarily induced phenomenon after a long-standing disease process.     

Rod distribution and muscle fiber type modification in the progression of nemaline myopathy

Nemaline myopathy is a structural congenital myopathy associated with the presence of rodlike structures inside the muscle fibers and type I predominance. It may be caused by mutations in at least five genes: slow alpha-tropomyosin 3 (chromosome 1q22-23), nebulin (chromosome 2q21.1-q22), actin (chromosome 1q42), tropomyosin 2 (chromosome 9p13), and troponin T1 (chromosome 19q13.4). The effect of these mutations in the expression of the protein and the mechanism of rod formation is still under investigation. We analyzed the possibility of progressive alterations with time and/or disease evolution, such as transformation of type I to type II fiber and rod pattern and distribution in muscle fibers from patients with nemaline myopathy, through a morphometric and immunohistochemical analysis of different muscle protein isoforms. A tendency of diffuse rods to be organized in the subsarcolemmal region was observed in two patients who were submitted to subsequent biopsies after 10 and 13 years. Additionally, we observed the expression of type II protein isoforms in type I fibers and a higher proportion of type II fibers in the younger patient of a pair of affected sibs, giving further support to the hypothesis of progressive conversion of type II to type I fibers in nemaline myopathy.     

Nemaline myopathy: comparative muscle histochemistry in the severe neonatal, moderate congenital, and adult-onset forms

A histochemical study of biopsied muscle specimens from patients with the 3 forms of nemaline myopathy (i.e., severe neonatal, moderate congenital, and adult-onset), classified on the basis of clinical symptoms, was conducted. A close relationship could not be found between the number of rods and the severity of weakness in any form. Type 1 fiber atrophy and predominance or type 2B fiber deficiency was the usual finding in all forms. In the moderate congenital form, type 1 fiber atrophy and predominance became more apparent in patients with a protracted course, suggesting that the histochemical abnormalities are progressive. The abnormal fiber type distribution is assumed to be related to the pathogenetic mechanism of nemaline myopathy in all forms. Because acid phosphatase activity was increased in muscle fibers of patients with rapid progression, an autodegenerative process inducing lysosomal enzyme activation may be responsible for the acute clinical progression and muscle fiber loss in this disorder.     

An adulthood progressive case of congenital nemaline myopathy showing rimmed vacuoles in muscle biopsy and diffuse neurogenic changes on electromyography]

A 29-year-old woman with benign congenital nemaline myopathy is reported. She did not walk until the age of one year and seven months. Although she acquired the ability to run, she ran very slowly. She first noticed the progression of weakness of the limbs at age 21, and it worsened gradually. On admission, she showed moderate weakness in the face, neck, and four limbs. Serum creatine kinase was elevated to 218 U/l. Needle electromyography showed giant and polyphasic motor unit potentials with a reduced reference pattern in the four limbs diffusely. In muscle biopsy, about 10% of fibers had many small vacuoles, and half of them were rimmed. Modified Gomori trichrome stain revealed nemaline rods in about 20% of both type I and type II fibers. Fibers with large diameter and atrophic ones showed increased acid phosphatase activity. Type I fibers were small, and type II fibers numbered only 2%. We diagnosed her illness as a congenital nemaline myopathy that began in infancy and progressed in adulthood. The increased autophagic activity probably caused the progression of muscle weakness. Moreover, the presence of both nemaline rods and rimmed vacuoles may have contributed to the development of diffuse neurogenic changes seen in electromyography.     

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. Muscle Nerve 39: 406–408, 2009     

Alpha-actinin and myosin light chains in congenital nemaline myopathy

The muscle fibers of patients with congenital nemaline myopathy contain nemaline bodies, of which alpha-actinin is a major constituent. In some cases, deficiencies of fast myosin light chains have been reported. We performed 1-dimensional polyacrylamide sodium dodecyl sulfate gradient gel electrophoresis of muscle proteins from 13 patients with congenital nemaline myopathy and 10 controls to examine the alpha-actinin and the distribution of myosin light chains in congenital nemaline myopathy. At 95 kd (corresponding to alpha-actinin), 4 patients and all controls had 1 band, 2 patients did not have any bands, and 7 had bands that were clearly weaker than those of the controls. Because alpha-actinin is present in the nemaline bodies of congenital nemaline myopathy muscle, only the deficiency of this protein must be apparent. No apparent differences in fast myosin light-chain distribution could be documented between patients and controls; no correlation was observed between muscle fiber type and light-chain distribution. The results suggest that alpha-actinin is abnormal in congenital nemaline myopathy.     

Familial nemaline myopathy

Two sisters with congenital nemaline myopathy are described. In both cases almost 70% of muscle fibers contained rods which were selectively localized in the larger ones. The variability coefficient was abnormally increased. Histochemical reactions showed that almost all the muscle fibers were type 1. In one case many fibers contained one or more core-like lesions. The parents and two siblings of the patients were clinically normal; EMG examination also showed normal motor unit potentials. Muscle biopsy was normal in the father; in the mother a slight type 1 predominance was detected without rods or other signs of myopathy. The disease seems to be transmitted by an autosomal recessive trait, although incomplete penetrance of a dominant trait cannot be excluded.     

Pathology of congenital nemaline myopathy. A follow-up study

This study was undertaken to review the development over 5-18 years of pathologic changes in 13 patients (4 male and 9 female) with congenital nemaline myopathy. Follow-up biopsies were compared with earlier biopsies and with published normal values as to quantity and location of nemaline bodies, secondary signs of myopathy, and in 6 patients as to muscle fiber type and size. Biopsy findings were correlated with the mobility and muscle power of the patient. The main differences in myofiber maturation in the patients as compared with normal myofiber maturation were: (1) deficient differentiation of type 2 fibers, (2) further increase of variation in fiber size with age, and (3) skewing in early adulthood of fiber size distribution curves toward the atrophic end. In ambulant patients, this skew seemed to be compensated with a population of hypertrophic fibers. The nemaline bodies tended to be located beneath the sarcolemma in the younger patients and inside the muscle fibers in the older patients. The quantity of nemaline bodies seemed to have increased with age. The clinical deterioration and the defective myofiber maturation in the patients together with an increase in internal nuclei and endomysial fat or fibrosis indicate an active disease process. This speaks against the generally held view that congenital nemaline myopathy is static.     

Follow-up of nemaline myopathy in two patients with novel mutations in the skeletal muscle alpha-actin gene (ACTA1)

Nemaline myopathy has been associated with mutations in five different genes, which all encode protein components of the sarcomeric thin filaments. We report follow-up studies in two children with mutations not previously described in skeletal muscle alpha-actin (ACTA1). Case 1 was a male patient who after birth suffered from pronounced muscle weakness and hypotonia. Muscle biopsy showed small fibers with numerous rods. He failed to achieve any motor milestones. At the age of 17 he required 24 h ventilator support. He could not lift his arms against gravity, but he could use his hands to control his electric wheelchair. The muscle biopsy showed marked replacement of muscle tissue by fat and connective tissue. Only few fibers showed nemaline rods. He had a de novo, heterozygous mutation, G268D in ACTA1. Case 2 was a female patient with feeding difficulties and mild hypotonia in the neonatal period. Muscle biopsy showed hypoplastic muscle fibers and numerous rods. At 11 years of age she walked and moved unhindered and could run fairly well. She had a de novo, heterozygous mutation, K373E, in ACTA1. These two patients illustrate the marked variability in the clinical features of nemaline myopathy in spite of similar muscle pathology in early childhood. The severe muscle atrophy with replacement of fat and connective tissue in case 1 demonstrates the progressive nature of nemaline myopathy in some cases. The described two mutations add to the previously reported mutations in ACTA1 associated with nemaline myopathy.     

杆状体肌病合并先天性单一Ⅰ型肌纤维肌病临床及病理报告

目的探讨杆状体肌病及单一Ⅰ型肌纤维肌病的临床及病理特点。方法杆状体肌病合并单一Ⅰ型肌纤维肌病患者行组织化学染色病理分析。结果肌肉活检modified Gomori trichrome（MGT）染色肌浆内、肌膜下紫色杆状体聚集ATPase染色（酸性、碱性）肌纤维类型几乎全部为Ⅰ型肌纤维，散在单个Ⅱ型肌纤维。结论肌活检发现特异性杆状体、单一型肌纤维分布是确诊此类疾病的唯一可靠方法。     

Clinical and pathological studies on nemaline myopathy in adulthood]

We examined 22 biopsied muscles from adult patients who had the histopathological characteristics of nemaline myopathy. In the first group, 13 patients had muscle weakness and/or skeletal abnormalities, such as high-arched palate, pes cavus and scoliosis which are often accompanied with the congenital nemaline myopathy. Their appropriate diagnosis had never been made until muscle biopsy was done, because of benign clinical course. In the second group, the symptoms of nine patients became manifest in adulthood and failed to show typical skeletal abnormalities. However, six muscle biopsies showed the histopathologic characteristics of congenital nemaline myopathy; abnormal fiber type distribution including type 1 fiber predominancy, type 1 fiber atrophy and type 2B fiber deficiency. Three patients remained in good health until adulthood when they developed muscle weakness with pathologic findings of nemaline myopathy. Accordingly, nemaline myopathy in adulthood can be categorized into three forms; the first two forms have clinical and pathologic evidence of the congenital benign form, whereas the symptoms are too mild to be noticed. The third form is not a hereditary disorder which may result from autoimmune pathophysiology.     

Severe neonatal nemaline myopathy with delayed maturation of muscle

A Japanese infant with a severe neonatal form of nemaline myopathy showed features of muscle immaturity as well as rods in the biopsied quadriceps femoris muscle, and involvement of diaphragm was first confirmed at autopsy. The biopsied muscle showed numerous rods in 80% of muscle fibers, and an increased number of type 2C fibers (23.2%). Electron microscopic findings were characterized by the presence of many small, immature round fibers with central nuclei and sparse myofibrils, and an increased number of satellite cells in close association with the small muscle fibers, as well as numerous rod structures. These microscopic and electron microscopic findings are interpreted as immature muscle fibers. Maturational delay or arrest implies deprivation of a development promoting factor such as a neuronal signal. Severe involvement with numerous rods was demonstrated in both diaphragm and intercostal muscles at the time of the postmortem examination, compatible with the patient's respiratory failure.     

Neonatal form of nemaline myopathy, muscle immaturity, and a microvascular injury

An infant with a neonatal form of nemaline myopathy showed ultrastructural features of muscle immaturity. Immaturity was characterized by an abnormal presence of myotubes, as well as cells in clusters within a common basement membrane and a great number of satellite cells adhering to very small muscle fibers. In addition, degenerative changes and a severe microvascular lesion were observed. The pathologic findings in the muscle of this patient were those of neonatal nemaline myopathy complicating severe microvascular injury, possibly induced by an unknown toxic agent.     

Mild phenotype of nemaline myopathy with sleep hypoventilation due to a mutation in the skeletal muscle alpha-actin (ACTA1) gene

Nemaline myopathy is a clinically and genetically heterogeneous condition. The clinical spectrum ranges from severe cases with antenatal or neonatal onset and early death to late onset cases with only slow progression. Three genes are known to cause nemaline myopathy: the genes for nebulin (NEB) on chromosome 2q22, slow alpha-tropomyosin (TPM3) on chromosome 1q21 and skeletal muscle alpha-actin (ACTA1) on chromosome 1q42. We present a 39-year-old lady with a mild form of nemaline myopathy, whom we have followed over a period of 25 years. She presented at the age of 7 years with symptoms of mild axial and proximal muscle weakness. The overall course was essentially static, but at 36 years, she went into life-threatening respiratory failure, for which she is currently treated with night-time ventilation. Muscle biopsies at 12, 17 and 39 years of age showed typical nemaline rods, particularly in type 1 fibres. Areas with unevenness of oxidative stain were present in the second and third biopsies. The presence of rods and core-like areas was confirmed on electron microscopy. There was no detectable alteration in actin expression immunocytochemically. A dominant missense mutation in the skeletal muscle alpha-actin gene (ACTA1) was found. This case illustrates the clinical and genetic heterogeneity of nemaline myopathy, and one phenotype of the wide spectrum of severity caused by mutations in the skeletal muscle alpha-actin (ACTA1) gene. In addition, it shows the diversity of pathological features that can occur in congenital myopathies due to mutations in the same gene.     

Congenital neuromuscular disease with uniform type 1 fibers : a case report

A 3-year-old boy was seen because of delayed developmental milestones, waddling gait, nonprogressive proximal muscle weakness and hyporeflexia. Serum creatine kinase levels were normal and EMG was non-diagnostic. Muscle biopsy revealed complete absence of type 2 A and 2 B fibers in addition to a moderate variation in fiber size. Diagnostic findings for congenital nonprogressive myopathies were not present such as nemaline bodies, cores, targetoid structure, central nuclei or selective type 1 fiber atrophy. This was the first case of a distinct form of non-progressive congenital myopathy, "congenital neuromuscular disease (myopathy) with uniform type 1 fibers", accompanied with mental retardation in Japan.     

Nemaline myopathy with type 2 fiber predominance; a case report]

A 4-year-old boy was admitted to our hospital because of dyspnea and muscle-weakness. His developmental milestones were delayed. His face was long with opened mouth. He spoke with nasal voice. He had proximally dominant muscle weakness and his deep tendon reflexes were absent. Laboratory examination revealed normal serum creatine kinase level and a myopathic EMG pattern. Blood gas analysis revealed metabolic acidosis with PH 7.35, PCO2 55.4 mmHg, PO2 62.4 mmHg, BE 3.0, probably from the metabolic acidosis by respiratory muscle weakness. In the biopsied left biceps brachii muscle, there were scattered fibers with nemaline bodies and abnormal fiber type distribution; type 1, 2 A, 2 B and 2 C fibers comprised 7%, 70%, 21% and 2% respectively. Small type 1 fibers and type 1 fiber predominance are the characteristic and common histochemical findings in nemaline myopathy. Accordingly, type 2 fiber predominance in the present patient is a unique, rare phenomenon. The finding might result from a preferential loss of type 1 motoneurons or muscle fiber type transformation from type 1 to type 2 fibers due to a certain abnormal neuronal influence on developing muscles.     

Follow-up studies in a case of unusual congenital myopathy,suggestive of nemaline type

Summary A 20-month-old boy — offspring of consanguinous parents, whose mother presumably had subclinical myopathy — presented with clinical signs of congenital non-progressive myopathy, neurogenic-myogenic electromyographic findings and normal motor conduction velocity. Biopsy of quadriceps muscle showed fiber-type disproportion with hypotrophic type 1, hypertrophic 2A and absent 2B fibers. Subsarcolemmal segmental foci of abnormally, in part regularly arranged bundles of mostly thin myofilaments were found in 13% of hypotrophic type 1 fibers. Rods were seen in only 1 fiber out of 20 tissue blocks. Reexamination 6 years later revealed slightly increased muscle force, myopathic EMG pattern and borderline motor and sensory nerve conduction velocities. Biopsy specimen from deltoid muscle consisted of untypable fibers of varying diameters with jagged Z-lines and increased variability of myofibrillar diameters. Multiple rods were present in 1% of the fibers, the formerly seen segmental foci in 0.1% only. Several intramuscular nerves were normal. The case contributes some new features to the spectrum of congenital myopathies of the nemaline type and suggests different stages of arrested maturation of type 1 fibers at least in this particular case.     

Actin-related myopathy without any missense mutation in the ACTA1 gene

Actinopathies are defined by missense mutations in the ACTA1 gene coding for sarcomeric actin, of which some 70 families have, so far, been identified. Often, but not always, muscle fibers carry large patches of actin filaments. Many such patients also have nemaline myopathy, qualifying actinopathies as a subgroup of nemaline myopathies. This article concerns a then newborn, now 2 1/2-year-old boy, the first and single child of nonconsanguineous parents, who was born floppy, requiring immediate postnatal assisted ventilation. A quadriceps muscle biopsy revealed large patches of thin myofilaments reacting at light and electron microscopic levels with antibodies against actin but only a few sarcoplasmic rods and no intranuclear rods. DNA analysis of the patient's and both parents' blood did not reveal any missense mutation in the ACTA1 gene. Thus, this congenital myopathy can be caused by a new type of ACTA1 gene mutation, a new non-ACTA1 gene mutation, or no mutation at all, designating it as an actin-related myopathy, perhaps a new type of congenital myopathy and a new member of protein aggregate myopathies marked by aggregation of proteins within muscle fibers, among them desminopathies, alpha-beta crystallinopathies, other desmin-related myopathies (also termed myofibrillar myopathies), actinopathies and, now, actin-related myopathies.     

A case of adult-onset nemaline myopathy (adult-onset rod disease) with distal muscular hypertrophy]

We reported a 40-year-old male with adult-onset nemaline myopathy (adult-onset rod disease) showing muscular hypertrophy of distal limbs. At the age of 25, he noticed thinness of his thighs. Difficulty in climbing stairs slowly progressed from the age of 35. On admission neurological examination revealed muscular weakness and atrophy of proximal limbs and hypertrophy of distal flexors. Normal laboratory tests included serum creatine kinase, myoglobin, aldolase and pyruvate. Electromyography revealed severe neurogenic changes in the right biceps brachial muscle and the right quadriceps muscle, and moderate changes in the right gastrocnemius. Biopsy specimen of the deltoid muscle demonstrated type 1 fiber predominance and type 1 fiber atrophy, and there was small group atrophy and type grouping. Abundant nemaline rods were found mainly in type 1 fibers (81.5%). In order to evaluate hypertrophy of calf muscles, T1-weighted MRI of lower extremity was performed. While transaxial images through mid thigh showed moderate fatty replacement, increased volume and little fatty replacement were found in the mid calf. Therefore, hypertrophy of the calf muscle seemed to be compensative hypertrophy. But in this case neurogenic factors were indicated electromyographically and histologically. These findings may advocate the notion that neurogenic factors involved not only congenital but adult-onset rod disease.     

Muscle weakness in respiratory and peripheral skeletal muscles in a mouse model for nebulin-based nemaline myopathy

Nemaline myopathy is among the most common non-dystrophic congenital myopathies, and is characterized by the presence of nemaline rods in skeletal muscles fibers, general muscle weakness, and hypotonia. Although respiratory failure is the main cause of death in nemaline myopathy, only little is known regarding the contractile strength of the diaphragm, the main muscle of inspiration. To investigate diaphragm contractility, in the present study we took advantage of a mouse model for nebulin-based nemaline myopathy that we recently developed. In this mouse model, exon 55 of Neb is deleted (Neb^ΔExon55), a mutation frequently found in patients. Diaphragm contractility was determined in permeabilized muscle fibers and was compared to the contractility of permeabilized fibers from three peripheral skeletal muscles: soleus, extensor digitorum longus, and gastrocnemius. The force generating capacity of diaphragm muscle fibers of Neb^ΔExon55 mice was reduced to 25% of wildtype levels, indicating severe contractile weakness. The contractile weakness of diaphragm fibers was more pronounced than that observed in soleus muscle, but not more pronounced than that observed in extensor digitorum longus and gastrocnemius muscles. The reduced muscle contractility was at least partly caused by changes in cross-bridge cycling kinetics which reduced the number of bound cross-bridges. The severe diaphragm weakness likely contributes to the development of respiratory failure in Neb^ΔExon55 mice and might explain their early, postnatal death.