Is muscle glycogenolysis impaired in X-linked phosphorylase b kinase deficiency?

OBJECTIVE: It is unclear to what extent muscle phosphorylase b kinase (PHK) deficiency is associated with exercise-related symptoms and impaired muscle metabolism, because 1) only four patients have been characterized at the molecular level, 2) reported symptoms have been nonspecific, and 3) lactate responses to ischemic handgrip exercise have been normal. METHODS: We studied a 50-year-old man with X-linked PHK deficiency using ischemic forearm and cycle ergometry exercise tests to define the derangement of muscle metabolism. We compared our findings with those in patients with McArdle disease and in healthy subjects. RESULTS: Sequencing of PHKA1 showed a novel pathogenic mutation (c.831G>A) in exon 7. There was a normal increase of plasma lactate during forearm ischemic exercise, but lactate did not change during dynamic, submaximal exercise in contrast to the fourfold increase in healthy subjects. Constant workload elicited a second wind in all patients with McArdle disease, but not in the patient with PHK deficiency. IV glucose administration appeared to improve exercise tolerance in the patient with PHK deficiency, but not to the same extent as in the patients with McArdle disease. Lipolysis was higher in the patient with PHK deficiency than in controls. CONCLUSION: These findings demonstrate that X-linked PHK deficiency causes a mild metabolic myopathy with blunted muscle glycogen breakdown and impaired lactate production during dynamic exercise, which impairs oxidative capacity only marginally. The different response of lactate to submaximal and maximal exercise is likely related to differential activation mechanisms for myophosphorylase.

Symptomatic distal myopathy with cardiomyopathy due to a MYH7 mutation.

Mutations in the myosin heavy chain gene (MYH7) can cause several distinct phenotypes depending on the location of the mutation: hypertrophic cardiomyopathy (several exons), myosin storage myopathy (exon 37/39) or Laing distal myopathy (exons 32-36). Here, we describe a unique combination of hypertrophic cardiomyopathy and hypertrophic distal myopathy in a family with a MYH7 Val606Met mutation (exon 16).

Skeletal muscle ultrasonography in children with a dysfunction in the oxidative phosphorylation system.

OBJECTIVE: The aim of this prospective study was to investigate the diagnostic value of quantitative skeletal muscle ultrasonography in children suspected of having a mitochondrial disorder. METHODS: Muscle thickness and quantitatively determined echo intensity of four muscles were established in 53 children with symptoms indicative of a mitochondrial disorder. RESULTS: A sensitivity of 25 to 46 % was found, depending on the chosen cut-off point (abnormal or borderline abnormal), with a specificity of 85 to 100 %. Except for one, all abnormal ultrasound scans were found in children over five years of age. Within the group of patients with a mitochondrial disorder, a significant correlation was found between muscle echo intensity and age (r = 0.38; p = 0.047). CONCLUSIONS: We conclude that skeletal muscle ultrasound can be of additional value in the diagnosis of children with suspected mitochondrial disorders, especially in children over five years of age. With its low sensitivity, it is not suitable for screening purposes. However, since all abnormal ultrasound scans were found in children with a mitochondrial disorder, and no significant correlation with the MDC score was found, muscle ultrasound can be used complementary to this scoring system to facilitate the decision-making in pursuing further invasive diagnostics.

Anti-signal recognition particle autoantibodies: marker of a necrotising myopathy.

OBJECTIVE: To elucidate the clinical importance of the anti-signal recognition particle (SRP) autoantibody in patients with myositis. METHODS: Retrospective systematic assessment of the clinical, laboratory and histological characteristics of 23 anti-SRP-positive patients from six European centres. Data were compared with a large group of anti-SRP-negative patients with myositis published previously. RESULTS: Clinically, patients with anti-SRP autoantibodies often had a severe symmetric proximal muscle weakness resulting in marked disability, dysphagia and highly elevated levels of serum creatine kinase. Three patients had typical dermatomyositis rashes. The disease was associated with the occurrence of extramuscular signs and symptoms including interstitial lung disease. No association was found with an increased risk of cardiac involvement, and the disease carried a reasonably favourable prognosis with most patients responding to treatment. None of the patients had the typical histological features of myositis. Most muscle biopsy specimens showed the presence of necrotic muscle fibres and no inflammatory infiltrates. CONCLUSIONS: Anti-SRP autoantibodies are associated with a syndrome of a necrotising myopathy in the spectrum of immune-mediated myopathies that differs from typical polymyositis. Further studies are needed to elucidate the pathogenesis and to clarify the role of the anti-SRP autoantibodies in this unique disease.

Relation between muscle fiber conduction velocity and fiber size in neuromuscular disorders.

To determine the relation between muscle fiber conduction velocity (MFCV) and muscle fiber diameter (MFD) in pathological conditions, we correlated invasively measured MFCV values with MFD data obtained from muscle needle biopsies in 96 patients with various neuromuscular disorders. MFCV was significantly correlated with MFD and independent of the underlying disorder. Pathological diameter changes were fiber-type dependent, with corresponding MFCVs. A linear equation expresses the relation well: MFCV (m/s)=0.043.MFD (microm)+0.83. We conclude that fiber diameter determines MFCV largely independent of the underlying neuromuscular disorders studied.

Histology of hereditary neuralgic amyotrophy.

We report the findings in five muscle and three sural nerve biopsies, and in one postmortem plexus specimen, from six patients with hereditary neuralgic amyotrophy (HNA). We found that the sensory nerves are definitely involved in HNA despite the mainly motor symptoms, and that lesions in nerves and muscles are more widespread throughout the peripheral nervous system than clinically presumed, but, simultaneously, very focally affect isolated fascicles within individual nerves.

Hypovitaminosis D-related myopathy in immigrant teenagers.

INTRODUCTION: Vitamin D deficiency resulting in a limb-girdle muscle weakness was diagnosed in three veiled immigrant teenage girls. PATIENTS: Three girls had a progressive muscle weakness and pain during a period varying from 6 months to two years. On examination limb girdle muscle weakness, predominantly of the lower extremities, without other neurological abnormalities was found. Serum examination showed a decreased level of vitamin D and phosphate and an increased alkaline phosphatase, and in two girls decreased calcium and increased parathyroid hormone levels were found. After supplementation with vitamin D, the pain subsided and muscle strength increased within weeks. Serum examination of the female relatives revealed eight persons with hypovitaminosis D, without any complaints. CONCLUSIONS: Vitamin D deficiency can result in a limb-girdle myopathy in veiled immigrant teenagers in the Netherlands. Vitamin D supplementation leads to rapid recovery of the muscle strength. The female relatives of these patients should be examined too.

Autosomal recessive oculopharyngodistal myopathy: a distinct phenotypical, histological, and genetic entity.

We present a 25 year follow up of two siblings with autosomal recessive (AR) oculopharyngodistal myopathy. Remarkable in these patients, in comparison with patients with oculopharyngeal muscular dystrophy (OPMD), are the earlier age of onset, severe facial weakness, external ophthalmoplegia early in the course of the disease, and distal weakness in the limbs. Histological features included basophilic-rimmed vacuoles, but the typical OPMD intranuclear filaments were absent. These clinical and histological characteristics are comparable with those of two Japanese patients with AR oculopharyngodistal myopathy. This myopathy has usually been described as an autosomal dominant (AD) muscle disorder. It shares some clinical and histological characteristics with OPMD, but most patients with AD oculopharyngodistal myopathy are genetically different. Here we exclude an expansion of the GCG repeat or any other mutation in the coding region of the PABPN1 gene (responsible for OPMD) in patients with AR oculopharyngodistal myopathy. From this we conclude that AR oculopharyngodistal myopathy is a distinct phenotypical, histological, and genetic entity.

Diagnostic value of MHC class I staining in idiopathic inflammatory myopathies.

BACKGROUND: Identification of mononuclear cellular infiltrates in skeletal muscle tissue is the histological cornerstone of the diagnosis of idiopathic inflammatory myopathy (IIM). However, these infiltrates are not always present. OBJECTIVE: To determine whether MHC class I antigen expression on the sarcolemma, which is absent in normal muscle tissue, is upregulated in IIM and could serve as an additional diagnostic test. METHODS: Expression of MHC class I antigens was studied in 224 muscle samples of 61 adult patients with IIM (9 dermatomyositis, 23 polymyositis, 29 inclusion body myositis) and 163 controls (normal subjects and patients with various neuromuscular disorders) in a prospective blinded manner. RESULTS: The sensitivity of the test for diagnosing IIM was 78% (95% confidence interval (CI), 66% to 88%), with a specificity of 95% (91% to 98%). The sensitivity before the start of immunosuppressive treatment was 89% (76% to 96%). The sensitivity was not changed by including all patients who had been on immunosuppressive treatment for less than four weeks before muscle biopsy (sensitivity 90% (79% to 97%)). False positive results were found in only seven controls (4%), six of whom had a muscular dystrophy. CONCLUSIONS: Detection of sarcolemmal MHC class I is a valid test for IIM. It is not affected by the short term use of immunosuppressive agents (less than four weeks) and it should be incorporated in the histological evaluation when the diagnosis of IIM is under consideration or needs to be excluded.

A locus on chromosome 15q for a dominantly inherited nemaline myopathy with core-like lesions.

Nemaline myopathy is a congenital neuromuscular disorder characterized by muscle weakness and the presence of nemaline rods. Five genes have now been associated with nemaline myopathy: alpha-tropomyosin-3 (TPM3), alpha-actin (ACTA1), nebulin (NEB), beta-tropomysin (TPM2) and troponin T (TNNT1). In addition, mutations in the ryanodine receptor gene (RYR1) have been associated with core-rod myopathy. Here we report linkage in two unrelated families, with a variant of nemaline myopathy, with associated core-like lesions. The clinical phenotype consists of muscle weakness in addition to a peculiar kind of muscle slowness. A genome-wide scan revealed a locus for nemaline myopathy with core-like lesions on chromosome 15q21-q23 for both families. Combining the two families gave a two-point LOD score of 10.65 for D15S993. The alpha-tropomyosin-1 gene (TPM1) located within this region is the strongest candidate gene. However, no mutations were found in the protein-coding region of TPM1, although small deletions or mutations in an intron cannot be excluded. The critical region contains few other candidate genes coding for muscle proteins and several genes of unknown function, and has not yet been sequenced completely. The novel phenotype of nemaline myopathy in the two presented families corresponds to an also novel, as yet uncharacterized, genotype.

A new phenotype of autosomal dominant nemaline myopathy.

We present a five-generation family with a novel phenotype of autosomal dominant nemaline myopathy not linked to the three genes known to be causative for nemaline myopathy (alpha-tropomyosin-3, nebulin, and alpha-actin). Although there was muscle weakness in the neck flexors and proximal muscles of the limbs, as found in other families, facial, ankle dorsiflexor and respiratory muscles were normal. The most remarkable clinical feature was a peculiar kind of slowness in movement not reported previously in nemaline myopathy.

Congenital fibre type disproportion a time-locked diagnosis: a clinical and morphological follow-up study.

This is the first report that describes the clinical and histological findings in a patient suffering from pure congenital fibre type disproportion (CFTD), who had two biopsies with an interval of 16 years. Additionally, we compared the clinical signs and symptoms of the present case to those of 35 CFTD cases reviewed from the literature. From this we conclude that smallness of type I fibre diameter is not a characteristic feature during the course of pure CFTD. This suggests that CFTD is a time-locked diagnosis.

A 4-base pair deletion in the mitochondrial cytochrome b gene associated with parkinsonism/MELAS overlap syndrome.

Five patients with diminished activity of complex III of the mitochondrial respiratory chain have been screened for mutations in the mitochondrial cytochrome b (cyt b) gene. In 1 patient, a young boy with an akinetic rigid syndrome and a mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS), a novel 4-base pair deletion was identified. This mutation in this highly conserved gene is considered to be pathogenic since it is a heteroplasmic frame shift mutation predicted to lead to a truncated protein.

Complex regional pain syndrome type I (RSD): pathology of skeletal muscle and peripheral nerve.

BACKGROUND: Reflex sympathetic dystrophy (RSD) (recently reclassified as complex regional pain syndrome type I) is a syndrome occurring in extremities and, when chronic, results in severe disability and untractable pain. RSD may be accompanied by neurologic symptoms even when there is no previous neurologic lesion. There is no consensus as to the pathogenic mechanism involved in RSD. To gain insight into the pathophysiology of RSD, we studied histopathology of skeletal muscle and peripheral nerve from patients with chronic RSD in a lower extremity. METHODS: In eight patients with chronic RSD, an above-the-knee amputation was performed because of a nonfunctional limb. Specimens of sural nerves, tibial nerves, common peroneal nerves, gastrocnemius muscles, and soleus muscles were obtained from the amputated legs and analyzed by light and electron microscopy. RESULTS: In all patients, the affected leg showed similar neurologic symptoms such as spontaneous pain, hyperpathy, allodynia, paresis, and anesthesia dolorosa. The nerves showed no consistent abnormalities of myelinated fibers. In four patients, the C-fibers showed electron microscopic pathology. In all patients, the gastrocnemius and soleus muscle specimens showed a decrease of type I fibers, an increase of lipofuscin pigment, atrophic fibers, and severely thickened basal membrane layers of the capillaries. CONCLUSION: In chronic RSD, efferent nerve fibers were histologically unaffected; from afferent fibers, only C-fibers showed histopathologic abnormalities. Skeletal muscle showed a variety of histopathologic findings, which are similar to the histologic abnormalities found in muscles of patients with diabetes.

Genetic characteristics of myoadenylate deaminase deficiency.

Two types of myoadenylate deaminase (MAD) deficiency have been described, primary or inherited, and secondary or acquired MAD deficiency. In this study, we investigated whether secondary MAD deficiency is indeed acquired or merely coincidental. We demonstrated the same underlying molecular defect, a C34T transition, in both types of deficiency. Furthermore, the same frequency of the mutant MAD allele was found in the general population as in patients with neuromuscular complaints. We therefore conclude that in the Dutch population, secondary MAD deficiency is merely a "coincidental" finding, and that MAD deficiency is a harmless genetic variant.