Search tips
Search criteria

Results 1-16 (16)

Clipboard (0)

Select a Filter Below

Year of Publication
author:("missing, John")
1.  Decreased Variability of the 6-Minute Walk Test by Heart Rate Correction in Patients with Neuromuscular Disease 
PLoS ONE  2014;9(12):e114273.
The 6-minute walk test is widely used to assess functional status in neurological disorders. However, the test is subject to great inter-test variability due to fluctuating motivation, fatigue and learning effects. We investigated whether inter-test variability of the 6MWT can be reduced by heart rate correction.
Sixteen patients with neuromuscular diseases, including Facioscapulohumeral muscular dystrophy, Limb-girdle muscular dystrophy, Charcot-Marie-Tooths, Dystrophia Myotonica and Congenital Myopathy and 12 healthy subjects were studied. Patients were excluded if they had cardiac arrhythmias, if they received drug treatment for hypertension or any other medical conditions that could interfere with the interpretation of the heart rate and walking capability. All completed three 6-minute walk tests on three different test-days. Heart rate was measured continuously.
Successive standard 6-minute walk tests showed considerable learning effects between Tests 1 and 2 (4.9%; P = 0.026), and Tests 2 and 3 (4.5%; P = 0.020) in patients. The same was seen in controls between Tests 1 and 2 (8.1%; P = 0.039)). Heart rate correction abolished this learning effect.
A modified 6-minute walk test, by correcting walking distance with average heart rate during walking, decreases the variability among repeated 6-minute walk tests, and should be considered as an alternative outcome measure to the standard 6-minute walk test in future clinical follow-up and treatment trials.
PMCID: PMC4257612  PMID: 25479403
2.  Bezafibrate in skeletal muscle fatty acid oxidation disorders 
Neurology  2014;82(7):607-613.
To assess whether bezafibrate increases fatty acid oxidation (FAO) and lowers heart rate (HR) during exercise in patients with carnitine palmitoyltransferase (CPT) II and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies.
This was a 3-month, randomized, double-blind, crossover study of bezafibrate in patients with CPT II (n = 5) and VLCAD (n = 5) deficiencies. Primary outcome measures were changes in FAO, measured with stable-isotope methodology and indirect calorimetry, and changes in HR during exercise.
Bezafibrate lowered low-density lipoprotein, triglyceride, and free fatty acid concentrations; however, there were no changes in palmitate oxidation, FAO, or HR during exercise.
Bezafibrate does not improve clinical symptoms or FAO during exercise in patients with CPT II and VLCAD deficiencies. These findings indicate that previous in vitro studies suggesting a therapeutic potential for fibrates in disorders of FAO do not translate into clinically meaningful effects in vivo.
Classification of evidence:
This study provides Class I evidence that bezafibrate 200 mg 3 times daily is ineffective in improving changes in FAO and HR during exercise in adults with CPT II and VLCAD deficiencies.
PMCID: PMC3963421  PMID: 24453079
3.  Muscle Atrophy Reversed by Growth Factor Activation of Satellite Cells in a Mouse Muscle Atrophy Model 
PLoS ONE  2014;9(6):e100594.
Muscular dystrophies comprise a large group of inherited disorders that lead to progressive muscle wasting. We wanted to investigate if targeting satellite cells can enhance muscle regeneration and thus increase muscle mass. We treated mice with hepatocyte growth factor and leukemia inhibitory factor under three conditions: normoxia, hypoxia and during myostatin deficiency. We found that hepatocyte growth factor treatment led to activation of the Akt/mTOR/p70S6K protein synthesis pathway, up-regulation of the myognic transcription factors MyoD and myogenin, and subsequently the negative growth control factor, myostatin and atrophy markers MAFbx and MuRF1. Hypoxia-induced atrophy was partially restored by hepatocyte growth factor combined with leukemia inhibitory factor treatment. Dividing satellite cells were three-fold increased in the treatment group compared to control. Finally, we demonstrated that myostatin regulates satellite cell activation and myogenesis in vivo following treatment, consistent with previous findings in vitro. Our results suggest, not only a novel in vivo pharmacological treatment directed specifically at activating the satellite cells, but also a myostatin dependent mechanism that may contribute to the progressive muscle wasting seen in severely affected patients with muscular dystrophy and significant on-going regeneration. This treatment could potentially be applied to many conditions that feature muscle wasting to increase muscle bulk and strength.
PMCID: PMC4070942  PMID: 24963862
4.  The cytochrome b p.278Y>C mutation causative of a multisystem disorder enhances superoxide production and alters supramolecular interactions of respiratory chain complexes 
Human Molecular Genetics  2013;22(11):2141-2151.
Cytochrome b is the only mtDNA-encoded subunit of the mitochondrial complex III (CIII), the functional bottleneck of the respiratory chain. Previously, the human cytochrome b missense mutation m.15579A>G, which substitutes the Tyr 278 with Cys (p.278Y>C), was identified in a patient with severe exercise intolerance and multisystem manifestations. In this study, we characterized the biochemical properties of cybrids carrying this mutation and report that the homoplasmic p.278Y>C mutation caused a dramatic reduction in the CIII activity and in CIII-driven mitochondrial ATP synthesis. However, the CI, CI + CIII and CII + CIII activities and the rate of ATP synthesis driven by the CI or CII substrate were only partially reduced or unaffected. Consistent with these findings, mutated cybrids maintained the mitochondrial membrane potential in the presence of oligomycin, indicating that it originated from the respiratory electron transport chain. The p.278Y>C mutation enhanced superoxide production, as indicated by direct measurements in mitochondria and by the imbalance of glutathione homeostasis in intact cybrids. Remarkably, although the assembly of CI or CIII was not affected, the examination of respiratory supercomplexes revealed that the amounts of CIII dimer and III2IV1 were reduced, whereas those of I1III2IVn slightly increased. We therefore suggest that the deleterious effects of p.278Y>C mutation on cytochrome b are palliated when CIII is assembled into the supercomplexes I1III2IVn, in contrast to when it is found alone. These findings underline the importance of supramolecular interactions between complexes for maintaining a basal respiratory chain activity and shed light to the molecular basis of disease manifestations associated with this mutation.
PMCID: PMC3652418  PMID: 23418307
5.  Quantitative Magnetic Resonance Imaging in Limb-Girdle Muscular Dystrophy 2I: A Multinational Cross-Sectional Study 
PLoS ONE  2014;9(2):e90377.
We conducted a prospective multinational study of muscle pathology using magnetic resonance imaging (MRI) in patients with limb-girdle muscular dystrophy 2I (LGMD2I). Thirty eight adult ambulant LGMD2I patients (19 male; 19 female) with genetically identical mutations (c.826C>A) in the fukutin-related protein (FKRP) gene were recruited. In each patient, T1-weighted (T1w) imaging was assessed by qualitative grading for 15 individual lower limb muscles and quantitative Dixon imaging was analysed on 14 individual lower limb muscles by region of interest analysis. We described the pattern and appearance of muscle pathology and gender differences, not previously reported for LGMD2I. Diffuse fat infiltration of the gastrocnemii muscles was demonstrated in females, whereas in males fat infiltration was more prominent in the medial than the lateral gastrocnemius (p = 0.05). In the anterior thigh of males, in contrast to females, median fat infiltration in the vastus medialis muscle (45.7%) exceeded that in the vastus lateralis muscle (11.2%) (p<0.005). MRI is non-invasive, objective and does not rely on patient effort compared to clinical and physical measures that are currently employed. We demonstrated (i) that the quantitative Dixon technique is an objective quantitative marker of disease and (ii) new observations of gender specific patterns of muscle involvement in LGMD2I.
PMCID: PMC3938727  PMID: 24587344
6.  Reduced ceramide synthase 2 activity causes progressive myoclonic epilepsy 
Ceramides are precursors of complex sphingolipids (SLs), which are important for normal functioning of both the developing and mature brain. Altered SL levels have been associated with many neurodegenerative disorders, including epilepsy, although few direct links have been identified between genes involved in SL metabolism and epilepsy.
We used quantitative real-time PCR, Western blotting, and enzymatic assays to determine the mRNA, protein, and activity levels of ceramide synthase 2 (CERS2) in fiibroblasts isolated from parental control subjects and from a patient diagnosed with progressive myoclonic epilepsy (PME). Mass spectrometry and fluorescence microscopy were used to examine the effects of reduced CERS2 activity on cellular lipid composition and plasma membrane functions.
We identify a novel 27 kb heterozygous deletion including the CERS2 gene in a proband diagnosed with PME. Compared to parental controls, levels of CERS2 mRNA, protein, and activity were reduced by ˜50% in fibroblasts isolated from this proband, resulting in significantly reduced levels of ceramides and sphingomyelins containing the very long-chain fatty acids C24:0 and C26:0. The change in SL composition was also reflected in a reduction in cholera toxin B immunofluorescence, indicating that membrane composition and function are altered.
We propose that reduced levels of CERS2, and consequently diminished levels of ceramides and SLs containing very long-chain fatty acids, lead to development of PME.
PMCID: PMC4212479  PMID: 25356388
7.  Quantitative Muscle MRI as an Assessment Tool for Monitoring Disease Progression in LGMD2I: A Multicentre Longitudinal Study 
PLoS ONE  2013;8(8):e70993.
Outcome measures for clinical trials in neuromuscular diseases are typically based on physical assessments which are dependent on patient effort, combine the effort of different muscle groups, and may not be sensitive to progression over short trial periods in slow-progressing diseases. We hypothesised that quantitative fat imaging by MRI (Dixon technique) could provide more discriminating quantitative, patient-independent measurements of the progress of muscle fat replacement within individual muscle groups.
To determine whether quantitative fat imaging could measure disease progression in a cohort of limb-girdle muscular dystrophy 2I (LGMD2I) patients over a 12 month period.
32 adult patients (17 male;15 female) from 4 European tertiary referral centres with the homozygous c.826C>A mutation in the fukutin-related protein gene (FKRP) completed baseline and follow up measurements 12 months later. Quantitative fat imaging was performed and muscle fat fraction change was compared with (i) muscle strength and function assessed using standardized physical tests and (ii) standard T1-weighted MRI graded on a 6 point scale.
There was a significant increase in muscle fat fraction in 9 of the 14 muscles analyzed using the quantitative MRI technique from baseline to 12 months follow up. Changes were not seen in the conventional longitudinal physical assessments or in qualitative scoring of the T1w images.
Quantitative muscle MRI, using the Dixon technique, could be used as an important longitudinal outcome measure to assess muscle pathology and monitor therapeutic efficacy in patients with LGMD2I.
PMCID: PMC3743890  PMID: 23967145
8.  Protein Turnover and Cellular Stress in Mildly and Severely Affected Muscles from Patients with Limb Girdle Muscular Dystrophy Type 2I 
PLoS ONE  2013;8(6):e66929.
Patients with Limb girdle muscular dystrophy type 2I (LGMD2I) are characterized by progressive muscle weakness and wasting primarily in the proximal muscles, while distal muscles often are spared. Our aim was to investigate if wasting could be caused by impaired regeneration in the proximal compared to distal muscles. Biopsies were simultaneously obtained from proximal and distal muscles of the same patients with LGMD2I (n = 4) and healthy subjects (n = 4). The level of past muscle regeneration was evaluated by counting internally nucleated fibers and determining actively regenerating fibers by using the developmental markers embryonic myosin heavy chain (eMHC) and neural cell adhesion molecule (NCAM) and also assessing satellite cell activation status by myogenin positivity. Severe muscle histopathology was occasionally observed in the proximal muscles of patients with LGMD2I whereas distal muscles were always relatively spared. No difference was found in the regeneration markers internally nucleated fibers, actively regenerating fibers or activation status of satellite cells between proximal and distal muscles. Protein turnover, both synthesis and breakdown, as well as cellular stress were highly increased in severely affected muscles compared to mildly affected muscles. Our results indicate that alterations in the protein turnover and myostatin levels could progressively impair the muscle mass maintenance and/or regeneration resulting in gradual muscular atrophy.
PMCID: PMC3696023  PMID: 23840556
9.  Mutation Spectrum in the Large GTPase Dynamin 2, and Genotype–Phenotype Correlation in Autosomal Dominant Centronuclear Myopathy 
Human mutation  2012;33(6):949-959.
Centronuclear myopathy (CNM) is a genetically heterogeneous disorder associated with general skeletal muscle weakness, type I fiber predominance and atrophy, and abnormally centralized nuclei. Autosomal dominant CNM is due to mutations in the large GTPase dynamin 2 (DNM2), a mechanochemical enzyme regulating cytoskeleton and membrane trafficking in cells. To date, 40 families with CNM-related DNM2 mutations have been described, and here we report 60 additional families encompassing a broad genotypic and phenotypic spectrum. In total, 18 different mutations are reported in 100 families and our cohort harbors nine known and four new mutations, including the first splice-site mutation. Genotype–phenotype correlation hypotheses are drawn from the published and new data, and allow an efficient screening strategy for molecular diagnosis. In addition to CNM, dissimilar DNM2 mutations are associated with Charcot–Marie–Tooth (CMT) peripheral neuropathy (CMTD1B and CMT2M), suggesting a tissue-specific impact of the mutations. In this study, we discuss the possible clinical overlap of CNM and CMT, and the biological significance of the respective mutations based on the known functions of dynamin 2 and its protein structure. Defects in membrane trafficking due to DNM2 mutations potentially represent a common pathological mechanism in CNM and CMT.
PMCID: PMC3374402  PMID: 22396310
centronuclear myopathy; congenital myopathy; Charcot–Marie–Tooth neuropathy; DNM2; ADCNM; CMTD1B; DI-CMTB; CMT2M; hereditary motor and sensory neuropathy type II; HMSNII; MTM1; myotubular myopathy; BIN1; RYR1; endocytosis
10.  A decline in PABPN1 induces progressive muscle weakness in Oculopharyngeal muscle dystrophy and in muscle aging 
Aging (Albany NY)  2013;5(6):412-426.
Oculopharyngeal muscular dystrophy (OPMD) is caused by trinucleotide repeat expansion mutations in Poly(A) binding protein 1 (PABPN1). PABPN1 is a regulator of mRNA stability and is ubiquitously expressed. Here we investigated how symptoms in OPMD initiate only at midlife and why a subset of skeletal muscles is predominantly affected. Genome-wide RNA expression profiles from Vastus lateralis muscles human carriers of expanded-PABPN1 at pre-symptomatic and symptomatic stages were compared with healthy controls. Major expression changes were found to be associated with age rather than with expression of expanded-PABPN1, instead transcriptomes of OPMD and elderly muscles were significantly similar (P<0.05). Using k-means clustering we identified age-dependent trends in both OPMD and controls, but trends were often accelerated in OPMD. We report an age-regulated decline in PABPN1 levels in Vastus lateralis muscles from the fifth decade. In concurrence with severe muscle degeneration in OPMD, the decline in PABPN1 accelerated in OPMD and was specific to skeletal muscles. Reduced PABPN1 levels (30% to 60%) in muscle cells induced myogenic defects and morphological signatures of cellular aging in proportion to PABPN1 expression levels. We suggest that PABPN1 levels regulate muscle cell aging and OPMD represents an accelerated muscle aging disorder.
PMCID: PMC3824410  PMID: 23793615
Type 2 diabetes; TCF7L2; centenarians; extreme phenotypes; age-related diseases
11.  Limitations of muscle biopsy in Pompe disease 
BMC Musculoskeletal Disorders  2013;14(Suppl 2):O5.
PMCID: PMC3666912
12.  Clinical presentation and mutations in Danish patients with Wilson disease 
This study describes the clinical presentation and diagnosis in all Danish patients (49, 41 unrelated) with Wilson disease (WND). On the basis of the number of diagnosed patients from 1990–2008, the prevalence was estimated to be 1:49 500. Among routinely used diagnostic tests, none were consistently indicative of WND, with the exception of the 24-h urine-Cu test, which is always outside the normal range. Mutations were identified in 100% of the screened ATP7B alleles (70 unrelated), including five novel mutations: p.1021K; p.G1158V; p.L1304F; IVS20-2A>G; Ex5_6del. In all, 70% of mutations were found in exons 8, 14, 17, 18, and 20. The most frequent mutation, p.H1069Q, comprised 18%. We propose a new and simple model that correlates genotype and age of onset. By assuming that the milder of two mutations is ‘functionally dominant' and determines the age of onset, we classified 25/27 mutations as either severe (age of onset <20 years) or moderate (age of onset >20 years), and correctly predicted the age of onset in 37/39 patients. This method should be tested in other Wilson populations.
PMCID: PMC3179371  PMID: 21610751
Wilson disease; ATP7B; mutations; genotype/phenotype; age of onset; Denmark
13.  Calpain 3 is important for muscle regeneration: Evidence from patients with limb girdle muscular dystrophies 
Limb girdle muscular dystrophy (LGMD) type 2A is caused by mutations in the CAPN3 gene and complete lack of functional calpain 3 leads to the most severe muscle wasting. Calpain 3 is suggested to be involved in maturation of contractile elements after muscle degeneration. The aim of this study was to investigate how mutations in the four functional domains of calpain 3 affect muscle regeneration.
We studied muscle regeneration in 22 patients with LGMD2A with calpain 3 deficiency, in five patients with LGMD2I, with a secondary reduction in calpain 3, and in five patients with Becker muscular dystrophy (BMD) with normal calpain 3 levels. Regeneration was assessed by using the developmental markers neonatal myosin heavy chain (nMHC), vimentin, MyoD and myogenin and counting internally nucleated fibers.
We found that the recent regeneration as determined by the number of nMHC/vimentin-positive fibers was greatly diminished in severely affected LGMD2A patients compared to similarly affected patients with LGMD2I and BMD. Whorled fibers, a sign of aberrant regeneration, was highly elevated in patients with a complete lack of calpain 3 compared to patients with residual calpain 3. Regeneration is not affected by location of the mutation in the CAPN3 gene.
Our findings suggest that calpain 3 is needed for the regenerative process probably during sarcomere remodeling as the complete lack of functional calpain 3 leads to the most severe phenotypes.
PMCID: PMC3338386  PMID: 22443334
Limb girdle muscular dystrophy; Calpain 3; Muscle regeneration; INF; Neonatal myosin heavy chain; Vimentin
14.  Deletion of exon 26 of the dystrophin gene is associated with a mild Becker muscular dystrophy phenotype 
Acta Myologica  2011;30(3):182-184.
With the possible introduction of exon skipping therapy in Duchenne muscular dystrophy, it has become increasingly important to know the role of each exon of the dystrophin gene to protein expression, and thus the phenotype. In this report, we present two related men with an unusually mild BMD associated with an exon 26 deletion. The proband, a 23-year-old man, had slightly delayed motor milestones, walking 1½ years old. He had no complaints of muscle weakness, but had muscle pain. Clinical examination revealed no muscle wasting or loss of power, but his CK was 1500-7000 U/l. Muscle biopsy showed dystrophic changes. He had comorbidity with dystonia, slight mental retardation, low stature and neuropathy. The brother of the proband's mother came to medical attention when he was 43 years old. He complained about muscle pain. On examination, a MRC grade 4+ hip extention palsy and a discrete calf hypertrophy was noted. Creatine kinase was normal or raised maximally to 500U/l. The muscle biopsy was myopathic with increased fiber size variation and many internal nuclei, but no dystrophy. No comorbidity was found. In both cases, western blot showed a reduced dystrophin band. Genetic evaluation revealed a deletion of exon 26 of the dystrophin gene in both. This is the first description of patients with a exon 26 deletion of the dystrophin gene. Assuming the proband's comorbidity is unrelated, exon 26 deletion results in a very mild phenotype. This might be of interest in planning exon skipping therapy for Duchenne muscular dystrophy. This report also shows that BMD may present with a normal CK.
PMCID: PMC3298095  PMID: 22616200
BMD; dystrophin; deletion; exon 26
15.  Level of muscle regeneration in limb-girdle muscular dystrophy type 2I relates to genotype and clinical severity 
Skeletal Muscle  2011;1:31.
The balance between muscle regeneration and ongoing degeneration is a relationship that greatly influences the progression of muscular dystrophy. Numerous factors may influence the muscle regeneration, but more information about the relationship between genotype, clinical severity and the ability to regenerate is needed.
Muscle biopsies were obtained from the tibialis anterior muscle, and frozen sections were stained for general histopathological and immunohistological evaluation. Differences between groups were considered statistical significant at P < 0.05 using Student's unpaired t-test.
We found that all patients with limb-girdle muscular dystrophy type 2I (LGMD2I) had a large number of internally nucleated fibers, a sign of previous regeneration. The level of expression of muscle-specific developmental proteins, such as neonatal myosin heavy chain (nMHC) and myogenin, was related to the clinical severity. Additionally, we found that the majority of nMHC-positive fibers did not stain positively for utrophin in patients who were compound heterozygous for the L276I mutation, suggesting that the predominant form of regeneration in these patients is fiber repair rather than formation of new fibers. Double staining showed that many smaller nMHC-positive fibers were positive for antibodies against the glycosylation on α-dystroglycan, suggesting that such glycosylation may be a result of muscle regeneration.
Severely affected patients with LGMD2I have a high level of muscle degeneration, which leads to a high rate of regeneration, but this is insufficient to change the imbalance between degeneration and regeneration, ultimately leading to progressive muscle wasting. Detailed information regarding the level and rate of muscle regeneration and potential obstructions of the regenerative pathway should be of use for future therapies involving satellite-cell activation.
PMCID: PMC3197566  PMID: 21970816
16.  Deregulation of the ubiquitin-proteasome system is the predominant molecular pathology in OPMD animal models and patients 
Skeletal Muscle  2011;1:15.
Oculopharyngeal muscular dystrophy (OPMD) is a late-onset progressive muscle disorder caused by a poly-alanine expansion mutation in the Poly(A) Binding Protein Nuclear 1 (PABPN1). The molecular mechanisms that regulate disease onset and progression are largely unknown. In order to identify molecular pathways that are consistently associated with OPMD, we performed an integrated high-throughput transcriptome study in affected muscles of OPMD animal models and patients. The ubiquitin-proteasome system (UPS) was found to be the most consistently and significantly OPMD-deregulated pathway across species. We could correlate the association of the UPS OPMD-deregulated genes with stages of disease progression. The expression trend of a subset of these genes is age-associated and therefore, marks the late onset of the disease, and a second group with expression trends relating to disease-progression. We demonstrate a correlation between expression trends and entrapment into PABPN1 insoluble aggregates of OPMD-deregulated E3 ligases. We also show that manipulations of proteasome and immunoproteasome activity specifically affect the accumulation and aggregation of mutant PABPN1. We suggest that the natural decrease in proteasome expression and its activity during muscle aging contributes to the onset of the disease.
PMCID: PMC3156638  PMID: 21798095

Results 1-16 (16)