Simone Spuler

Fatal Cardiac Arrhythmia and Long-QT Syndrome in a New Form of Congenital Generalized Lipodystrophy with Muscle Rippling (CGL4) Due to PTRF-CAVIN Mutations

We investigated eight families with a novel subtype of congenital generalized lipodystrophy (CGL4) of whom five members had died from sudden cardiac death during their teenage years. ECG studies revealed features of long-QT syndrome, bradycardia, as well as supraventricular and ventricular tachycardias. Further symptoms comprised myopathy with muscle rippling, skeletal as well as smooth-muscle hypertrophy, leading to impaired gastrointestinal motility and hypertrophic pyloric stenosis in some children. Additionally, we found impaired bone formation with osteopenia, osteoporosis, and atlanto-axial instability. Homozygosity mapping located the gene within 2 Mbp on chromosome 17. Prioritization of 74 candidate genes with GeneDistiller for high expression in muscle and adipocytes suggested PTRF-CAVIN (Polymerase I and transcript release factor/Cavin) as the most probable candidate leading to the detection of homozygous mutations (c.160delG, c.362dupT). PTRF-CAVIN is essential for caveolae biogenesis. These cholesterol-rich plasmalemmal vesicles are involved in signal-transduction and vesicular trafficking and reside primarily on adipocytes, myocytes, and osteoblasts. Absence of PTRF-CAVIN did not influence abundance of its binding partner caveolin-1 and caveolin-3. In patient fibroblasts, however, caveolin-1 failed to localize toward the cell surface and electron microscopy revealed reduction of caveolae to less than 3%. Transfection of full-length PTRF-CAVIN reestablished the presence of caveolae. The loss of caveolae was confirmed by Atomic Force Microscopy (AFM) in combination with fluorescent imaging. PTRF-CAVIN deficiency thus presents the phenotypic spectrum caused by a quintessential lack of functional caveolae.

Mutations of the FHL1 Gene Cause Emery-Dreifuss Muscular Dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a rare disorder characterized by early joint contractures, muscular dystrophy, and cardiac involvement with conduction defects and arrhythmias. So far, only 35% of EDMD cases are genetically elucidated and associated with EMD or LMNA gene mutations, suggesting the existence of additional major genes. By whole-genome scan, we identified linkage to the Xq26.3 locus containing the FHL1 gene in three informative families belonging to our EMD- and LMNA-negative cohort. Analysis of the FHL1 gene identified seven mutations, in the distal exons of FHL1 in these families, three additional families, and one isolated case, which differently affect the three FHL1 protein isoforms: two missense mutations affecting highly conserved cysteines, one abolishing the termination codon, and four out-of-frame insertions or deletions. The predominant phenotype was characterized by myopathy with scapulo-peroneal and/or axial distribution, as well as joint contractures, and associated with a peculiar cardiac disease characterized by conduction defects, arrhythmias, and hypertrophic cardiomyopathy in all index cases of the seven families. Heterozygous female carriers were either asymptomatic or had cardiac disease and/or mild myopathy. Interestingly, four of the FHL1-mutated male relatives had isolated cardiac disease, and an overt hypertrophic cardiomyopathy was present in two. Expression and functional studies demonstrated that the FHL1 proteins were severely reduced in all tested patients and that this was associated with a severe delay in myotube formation in the two patients for whom myoblasts were available. In conclusion, FHL1 should be considered as a gene associated with the X-linked EDMD phenotype, as well as with hypertrophic cardiomyopathy.

Clinical features of facioscapulohumeral muscular dystrophy 2.

Objective: In some 5% of patients with facioscapulohumeral muscular dystrophy (FSHD), no D4Z4 repeat contraction on chromosome 4q35 is observed. Such patients, termed patients with FSHD2, show loss of DNA methylation and heterochromatin markers at the D4Z4 repeat that are similar to patients with D4Z4 contractions (FSHD1). This commonality suggests that a change in D4Z4 chromatin structure unifies FSHD1 and FSHD2. The aim of our study was to critically evaluate the clinical features in patients with FSHD2 in order to establish whether these patients are phenotypically identical to FSHD1 and to establish the effects of the (epi-) genotype on the phenotype. Methods: This cross-sectional study studied 33 patients with FSHD2 from 27 families, the largest cohort described to date. All patients were clinically assessed using a standardized clinical evaluation form. Genotype analysis was performed by pulsed field gel electrophoresis and PCR; D4Z4 methylation was studied by methylation-sensitive Southern blot analysis. Results: FSHD2 is identical to FSHD1 in its clinical presentation. Notable differences include a higher incidence (67%) of sporadic cases and the absence of gender differences in disease severity in FSHD2. Overall, average disease severity in FSHD2 was similar to that reported in FSHD1 and was not influenced by D4Z4 repeat size. In FSHD2, a small effect of the degree of hypomethylation on disease severity was observed. Conclusions: Clinically, patients with FSHD2 are indistinguishable from patients with FSHD1. The present data suggest that FSHD1 and FSHD2 are the result of the same pathophysiologic process.

Free Fatty Acids Link Metabolism and Regulation of the Insulin-Sensitizing Fibroblast Growth Factor-21

OBJECTIVE Fibroblast growth factor (FGF)-21 improves insulin sensitivity and lipid metabolism in obese or diabetic animal models, while human studies revealed increased FGF-21 levels in obesity and type 2 diabetes. Given that FGF-21 has been suggested to be a peroxisome proliferator–activator receptor (PPAR) α–dependent regulator of fasting metabolism, we hypothesized that free fatty acids (FFAs), natural agonists of PPARα, might modify FGF-21 levels. RESEARCH DESIGN AND METHODS The effect of fatty acids on FGF-21 was investigated in vitro in HepG2 cells. Within a randomized controlled trial, the effects of elevated FFAs were studied in 21 healthy subjects (13 women and 8 men). Within a clinical trial including 17 individuals, the effect of insulin was analyzed using an hyperinsulinemic-euglycemic clamp and the effect of PPARγ activation was studied subsequently in a rosiglitazone treatment trial over 8 weeks. RESULTS Oleate and linoleate increased FGF-21 expression and secretion in a PPARα-dependent fashion, as demonstrated by small-interfering RNA–induced PPARα knockdown, while palmitate had no effect. In vivo, lipid infusion induced an increase of circulating FGF-21 in humans, and a strong correlation between the change in FGF-21 levels and the change in FFAs was observed. An artificial hyperinsulinemia, which was induced to delineate the potential interaction between elevated FFAs and hyperinsulinemia, revealed that hyperinsulinemia also increased FGF-21 levels in vivo, while rosiglitazone treatment had no effect. CONCLUSIONS The results presented here offer a mechanism explaining the induction of the metabolic regulator FGF-21 in the fasting situation but also in type 2 diabetes and obesity.

Immortalized pathological human myoblasts: towards a universal tool for the study of neuromuscular disorders

BackgroundInvestigations into both the pathophysiology and therapeutic targets in muscle dystrophies have been hampered by the limited proliferative capacity of human myoblasts. Isolation of reliable and stable immortalized cell lines from patient biopsies is a powerful tool for investigating pathological mechanisms, including those associated with muscle aging, and for developing innovative gene-based, cell-based or pharmacological biotherapies.MethodsUsing transduction with both telomerase-expressing and cyclin-dependent kinase 4-expressing vectors, we were able to generate a battery of immortalized human muscle stem-cell lines from patients with various neuromuscular disorders.ResultsThe immortalized human cell lines from patients with Duchenne muscular dystrophy, facioscapulohumeral muscular dystrophy, oculopharyngeal muscular dystrophy, congenital muscular dystrophy, and limb-girdle muscular dystrophy type 2B had greatly increased proliferative capacity, and maintained their potential to differentiate both in vitro and in vivo after transplantation into regenerating muscle of immunodeficient mice.ConclusionsDystrophic cellular models are required as a supplement to animal models to assess cellular mechanisms, such as signaling defects, or to perform high-throughput screening for therapeutic molecules. These investigations have been conducted for many years on cells derived from animals, and would greatly benefit from having human cell models with prolonged proliferative capacity. Furthermore, the possibility to assess in vivo the regenerative capacity of these cells extends their potential use. The innovative cellular tools derived from several different neuromuscular diseases as described in this report will allow investigation of the pathophysiology of these disorders and assessment of new therapeutic strategies.

Beyond the sarcomere: CSRP3 mutations cause hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a frequent genetic cardiac disease and the most common cause of sudden cardiac death in young individuals. Most of the currently known HCM disease genes encode sarcomeric proteins. Previous studies have shown an association between CSRP3 missense mutations and either dilated cardiomyopathy (DCM) or HCM, but all these studies were unable to provide comprehensive genetic evidence for a causative role of CSRP3 mutations. We used linkage analysis and identified a CSRP3 missense mutation in a large German family affected by HCM. We confirmed CSRP3 as an HCM disease gene. Furthermore, CSRP3 missense mutations segregating with HCM were identified in four other families. We used a newly designed monoclonal antibody to show that muscle LIM protein (MLP), the protein encoded by CSRP3, is mainly a cytosolic component of cardiomyocytes and not tightly anchored to sarcomeric structures. Our functional data from both in vitro and in vivo analyses suggest that at least one of MLPs mutated forms seems to be destabilized in the heart of HCM patients harbouring a CSRP3 missense mutation. We also present evidence for mild skeletal muscle disease in affected persons. Our results support the view that HCM is not exclusively a sarcomeric disease and also suggest that impaired mechano-sensory stress signalling might be involved in the pathogenesis of HCM.

Unexpected sarcolemmal complement membrane attack complex deposits on nonnecrotic muscle fibers in muscular dystrophies

Antibody-dependent complement-mediated muscle fiber injury is a hypothetical immune effector response in inflammatory muscle diseases. Moreover, a sarcolemmal alteration in muscular dystrophies might trigger antibody-independent activation of the alternative complement pathway. We therefore searched for C5b9 complement membrane attack complex (MAC), immunoglobulin (Ig)G, and IgM deposits on nonnecrotic muscle fibers in muscle specimens from 81 patients with inflammatory myopathies, 45 patients with muscular dystrophies, and 19 patients with necrotizing myopathies. Sarcolemmal MAC deposits were present on nonnecrotic fibers (C+ fibers) in only two unusual types of inflammatory myopathy. By contrast, seven of 17 facioscapulohumeral dystrophy, four of nine limb-girdle dystrophy, and three of six merosin (laminin-α-2)-positive congenital muscular dystrophy but none of the Becker or Duchenne dystrophy specimens harbored C+ fibers. None of the C+ fibers immunostained for IgG or IgM, and none failed to immunostain for CD59 or CD46-inhibitors of the complement cascade. Our findings do not support a role for antibody-dependent complement-mediated muscle fiber injury in the major inflammatory muscle diseases. The cause and pathogenetic significance of the C+ fibers in the different types of muscular dystrophies remains to be elucidated.

Critical illness myopathy is frequent: accompanying neuropathy protracts ICU discharge

Objectives Neuromuscular dysfunction in critically ill patients is attributed to either critical illness myopathy (CIM) or critical illness polyneuropathy (CIP) or a combination of both. However, it is unknown whether differential diagnosis has an impact on prognosis. This study investigates whether there is an association between the early differentiation of CIM versus CIP and clinical prognosis. Methods The authors included mechanically ventilated patients who featured a Simplified Acute Physiology Score II (SAPS-II) ≥20 on three consecutive days within the first week after intensive care unit (ICU) admission. Fifty-three critically ill patients were enrolled and examined by conventional nerve-conduction studies and direct muscle stimulation (184 examinations in total). The first examination was conducted within the first week after admission to the ICU. Results In this cohort of critically ill patients, CIM was more frequent (68%) than CIP (38%). Electrophysiological signs of CIM preceded electrophysiological signs of CIP (median at day 7 in CIM patients vs day 10 in CIP patients, p<0.001). Most patients with CIP featured concomitant CIM. At discharge from ICU, 25% of patients with isolated CIM showed electrophysiological signs of recovery and significantly lower degrees of weakness. Recovery could not be observed in patients with combined CIM/CIP, even though the ICU length of stay was significantly longer (mean 35 days in CIM/CIP vs mean 19 days in CIM, p<0.001). Conclusion Prognoses of patients differ depending on electrophysiological findings during early critical illness: early electrophysiological differentiation of ICU acquired neuromuscular disorder enhances the evaluation of clinical prognosis during critical illness.

Nonexcitable muscle membrane predicts intensive care unit-acquired paresis in mechanically ventilated, sedated patients.

Objectives:To investigate the predictive value of electrophysiological measurements including validation of muscle membrane excitability on the development of intensive care unit (ICU)-aquired paresis. Design:Prospective observational study. Setting:University ICU. Patients:Surgical ICU patients selected upon a simplified acute physiology score ≥20 on three successive days within 1 wk after ICU admission. Interventions:We performed serial electrophysiological measurements with onset of critical illness including conventional electrophysiological parameters and compound muscle action potentials after direct muscle stimulation (dmCMAP). Patients’ awareness and muscle strength were measured sequentially by Ramsay sedation scale and an additional questionnaire and by Medical Research Council score, respectively. Measurements and Main Results:Among 56 sedated patients 34 patients revealed reduced dmCMAP values <3 mV indicating a myopathic process within 7.5 (5 of 11) days after admission to the ICU. Abnormal dmCMAP anticipated ICU-acquired paresis upon emergence from sedation with a sensitivity and specificity of 83.3% and 88.8%, respectively (positive predictive value of 0.91). Multivariate logistic regression analyses revealed that validating dmCMAP during early course of critical illness had significant diagnostic utility to anticipate ICU-acquired paresis (p = .004; odds ratio = .47; 95% confidence interval = .28–.79). Conclusions:Abnormal dmCMAP occurred within the first week after admission to the ICU and pointed towards a myopathic process as the primary cause of ICU-acquired paresis. Validation of dmCMAP with onset of critical illness allows an early prediction of ICU-acquired paresis and adds important information to clinical estimation of the patients’ motor function.

The role of autoimmune T lymphocytes in the pathogenesis of multiple sclerosis

Autoimmune T cells play a key role as regulators and effectors of autoimmune disease.In multiple sclerosis (MS), activated T cells specific for myelin components or other locally expressed autoantigens enter the CNS and recognize their antigen(s) on local antigen-presenting cells. After local stimulation, the T cells produce a plethora of cytokines and inflammatory mediators that have profound effects on the local cellular environment, induce and recruit additional inflammatory cells, and contribute to myelin damage. An increasingly detailed knowledge of these processes will greatly facilitate the development of new immunotherapies. This article focuses on the role of T cells in MS. We provide a brief overview of the principles of T-cell immunology, discuss the experimental techniques available for studying T cells, address the role of T cells in the pathogenesis of MS, and highlight modern concepts for immunotherapy. NEUROLOGY 1995;45(Suppl 6): S33-S38