Diagnosis of muscle diseases presenting with early respiratory failure

Improved diagnostic performance of high-sensitivity cardiac troponins in muscle dystrophies using comprehensive definition criteria for cardiac involvement: A longitudinal study on 35 patients

BACKGROUND AND PURPOSE

Sparse information is available on the correct interpretation of elevated high-sensitivity cardiac troponin (hs-cTn) in confirmed muscular dystrophies.

METHODS

Serum concentrations of hs-cTn T (hs-cTnT) and hs-cTn I (hs-cTnI) were determined in 35 stable outpatients with confirmed skeletal muscle dystrophies. We calculated sensitivities, specificities, and positive and negative predictive values of hs-cTnT and hs-cTnI for identification of cardiac involvement using a comprehensive definition that included diastolic left ventricular and right ventricular function, strain analysis using two-dimensional transthoracic echocardiogram and magnetic resonance imaging, myocardial biopsies, and consideration of a variety of triggers for cardiac injury, including arrhythmias, conduction disorders, and hypoxemia due to respiratory failure.

RESULTS

Cardiac involvement was diagnosed in 34 of 35 cases. Specificities of hs-cTnT increased from 12.5% to 100% (p = 0.0006) applying the comprehensive definition compared to a definition based on electrocardiography and echocardiography alone. At the recommended 99th percentile upper limit of normal, sensitivities were significantly lower for hs-cTnI than for hs-cTnT (29.4% vs. 100%, p = 0.0164). Conversely, the specificities of hs-cTnT and hs-cTnI increased to 100% when using the comprehensive definition criteria for diagnosing cardiac involvement.

CONCLUSIONS

Elevated hs-cTnT but not hs-cTnI discriminates cardiac involvement in cases with confirmed skeletal muscle dystrophies with very high sensitivity and 100% specificity. Prior reports on worse performance may be explained by the use of less sensitive imaging methods or incomplete assessment of cardiac involvement.

Update on recent advances in amyotrophic lateral sclerosis

In the last few years, our understanding of disease molecular mechanisms underpinning ALS has advanced greatly, allowing the first steps in translating into clinical practice novel research findings, including gene therapy approaches. Similarly, the recent advent of assistive technologies has greatly improved the possibility of a more personalized approach to supportive and symptomatic care, in the context of an increasingly complex multidisciplinary line of actions, which remains the cornerstone of ALS management. Against this rapidly growing background, here we provide an comprehensive update on the most recent studies that have contributed towards our understanding of ALS pathogenesis, the latest results from clinical trials as well as the future directions for improving the clinical management of ALS patients.

Dynamic equilibrium of skeletal muscle macrophage ontogeny in the diaphragm during homeostasis, injury, and recovery

The diaphragm is a unique skeletal muscle due to its continuous activation pattern during the act of breathing. The ontogeny of macrophages, pivotal cells for skeletal muscle maintenance and regeneration, is primarily based on two distinct origins: postnatal bone marrow-derived monocytes and prenatal embryonic progenitors. Here we employed chimeric mice to study the dynamics of these two macrophage populations under different conditions. Traditional chimeric mice generated through whole body irradiation showed virtually complete elimination of the original tissue-resident macrophage pool. We then developed a novel method which employs lead shielding to protect the diaphragm tissue niche from irradiation. This allowed us to determine that up to almost half of tissue-resident macrophages in the diaphragm can be maintained independently from bone marrow-derived monocytes under steady-state conditions. These findings were confirmed by long-term (5 months) parabiosis experiments. Acute diaphragm injury shifted the macrophage balance toward an overwhelming predominance of bone marrow (monocyte)-derived macrophages. However, there was a remarkable reversion to the pre-injury ontological landscape after diaphragm muscle recovery. This diaphragm shielding method permits analysis of the dynamics of macrophage origin and corresponding function under different physiological and pathological conditions. It may be especially useful for studying diseases which are characterized by acute or chronic injury of the diaphragm and accompanying inflammation.

Peripheral nervous system and neuromuscular disorders in the emergency department: A review

INTRODUCTION

Acute presentations and emergencies in neuromuscular disorders (NMDs) often challenge clinical acumen. The objective of this review is to refine the reader's approach to history taking, clinical localization and early diagnosis, as well as emergency management of neuromuscular emergencies.

METHODS

An extensive literature search was performed to identify relevant studies. We prioritized meta-analysis, systematic reviews, and position statements where possible to inform any recommendations.

SUMMARY

The spectrum of clinical presentations and etiologies ranges from neurotoxic envenomation or infection to autoimmune disease such as Guillain-Barré Syndrome (GBS) and myasthenia gravis (MG). Delayed diagnosis is not uncommon when presentations occur "de novo," respiratory failure is dominant or isolated, or in the case of atypical scenarios such as GBS variants, severe autonomic dysfunction, or rhabdomyolysis. Diseases of the central nervous system, systemic and musculoskeletal disorders can mimic presentations in neuromuscular disorders.

CONCLUSIONS

Fortunately, early diagnosis and management can improve prognosis. This article provides a comprehensive review of acute presentations in neuromuscular disorders relevant for the emergency physician.

"De Novo" Hypercapnic Respiratory Failure Unmasking Neuromuscular Disorders: Experiences From a Tertiary Care Center and Review of Literature

OBJECTIVES

Neuromuscular disorders could have respiratory involvement early or late into illness. Rarely, patients may present with a hypercapnic respiratory failure (with minimal motor signs) unmasking an underlying disease. There are hardly any studies which have addressed the spectrum and challenges involved in management of this subset, especially in the real-world scenario.

METHODS

A retrospective study comprising consecutive patients hospitalized with hypercapnic respiratory failure as the sole/dominant manifestation. The clinical-electrophysiological spectrum, phrenic conductions, diaphragm thickness, and outcomes were analyzed.

RESULTS

Twenty-seven patients were included, the mean age was 47.29 (SD 15.22) years, and the median duration of respiratory symptoms was 2 months (interquartile range [IQR] 1-4). Orthopnea was present in 23 patients (85.2%) and encephalopathy in 8 patients (29.6%). Phrenic nerve latencies and amplitudes were abnormal in 83.3% and 95.6%, respectively. Abnormal diaphragm thickness was noted in 78.5%. Based on a comprehensive electrophysiological strategy and paraclinical tests, an etiology was established in all. Reversible etiologies were identified in 17 patients (62.9%). These included myasthenia gravis (anti-AChR and MuSK), inflammatory myopathy, riboflavin transporter deficiency neuronopathy, Pompe disease, bilateral phrenic neuritis, and thyrotoxicosis. Respiratory onset motor neuron disease was diagnosed in 8 patients (29.6%). Despite diaphragmatic involvement, a functional respiratory recovery was noted at discharge (45%) and last follow-up (60%). Predictors for good outcomes included female sex, normal nerve conductions, and recent-onset respiratory symptoms.

DISCUSSION

A good functional recovery was noted in most of the patients including respiratory onset motor neuron disease. A systematic algorithmic approach helps in proper triaging, early diagnosis, and treatment. Clinical and electrodiagnostic challenges and observations from a tertiary care referral center are discussed.

Gustavson syndrome is caused by an in-frame deletion in RBMX associated with potentially disturbed SH3 domain interactions

RNA binding motif protein X-linked (RBMX) encodes the heterogeneous nuclear ribonucleoprotein G (hnRNP G) that regulates splicing, sister chromatid cohesion and genome stability. RBMX knock down experiments in various model organisms highlight the gene's importance for brain development. Deletion of the RGG/RG motif in hnRNP G has previously been associated with Shashi syndrome, however involvement of other hnRNP G domains in intellectual disability remain unknown. In the current study, we present the underlying genetic and molecular cause of Gustavson syndrome. Gustavson syndrome was first reported in 1993 in a large Swedish five-generation family presented with profound X-linked intellectual disability and an early death. Extensive genomic analyses of the family revealed hemizygosity for a novel in-frame deletion in RBMX in affected individuals (NM_002139.4; c.484_486del, p.(Pro162del)). Carrier females were asymptomatic and presented with skewed X-chromosome inactivation, indicating silencing of the pathogenic allele. Affected individuals presented minor phenotypic overlap with Shashi syndrome, indicating a different disease-causing mechanism. Investigation of the variant effect in a neuronal cell line (SH-SY5Y) revealed differentially expressed genes enriched for transcription factors involved in RNA polymerase II transcription. Prediction tools and a fluorescence polarization assay imply a novel SH3-binding motif of hnRNP G, and potentially a reduced affinity to SH3 domains caused by the deletion. In conclusion, we present a novel in-frame deletion in RBMX segregating with Gustavson syndrome, leading to disturbed RNA polymerase II transcription, and potentially reduced SH3 binding. The results indicate that disruption of different protein domains affects the severity of RBMX-associated intellectual disabilities.

Respiratory failure as first presentation of myasthenia gravis: a case report

Myasthenia gravis (MG) is often complicated by respiratory failure, an exacerbation known as myasthenic crisis. However, most patients with MG develop respiratory symptoms during the late course of the disease. Respiratory failure as an exclusive initial and primary complaint in patients with MG is rare and seldom reported. We herein describe a woman in her late 50s who presented with respiratory failure and was diagnosed with obesity hypoventilation syndrome at a local hospital. Her condition gradually worsened during the next 4 months and became accompanied by dysphagia. After 1 year of medical investigation, she was diagnosed in our hospital. A high level of anti-muscle-specific receptor tyrosine kinase antibody was found in her serum, and stimulation and electromyography results suggested MG. The patient's symptoms were improved by intravenous immunoglobulin and hormone therapy. This case reminds physicians to consider MG when encountering a patient who initially presents with respiratory failure.

Targeted next-generation sequencing determined a novel SGCG variant that is associated with limb-girdle muscular dystrophy type 2C: A case report

Limb-girdle muscular dystrophy-type 2C (LGMD2C) is caused by mutations in the SGCG gene. Here, we report a case of a 26-year-old male who had inactive walking due to proximal muscle weakness. Targeted next-generation sequencing found a novel variant c.412C > T (Q138*) in the SGCG gene.

A late presentation of TPM3 myopathy presenting as sleep hypoventilation in the setting of acute demyelinating encephalomyelitis

Central hypoventilation is a rare cause of respiratory failure that has been associated with multiple underlying disorders, including congenital central hypoventilation syndrome, obesity hypoventilation syndrome, and several neuromuscular conditions. We report the case of an adolescent who presented with respiratory failure in the setting of acute demyelinating encephalomyelitis whose clinical history was consistent with a congenital myopathy and whom we found to have a Tropomyosin 3 (TPM3) genetic variant on further genetic testing. This case expands the clinical spectrum of causes for late-onset central hypoventilation in the setting of a neuromuscular disorder.

CITATION

Stringel V, Bizargity P, Laureta E, Kothare S. A late presentation of TPM3 myopathy presenting as sleep hypoventilation in the setting of acute demyelinating encephalomyelitis. J Clin Sleep Med. 2022;18(11):2695-2698.

Learning Prognostic Models Using Disease Progression Patterns: Predicting the Need for Non-Invasive Ventilation in Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis is a devastating neurodegenerative disease causing rapid degeneration of motor neurons and usually leading to death by respiratory failure. Since there is no cure, treatment's goal is to improve symptoms and prolong survival. Non-invasive Ventilation (NIV) is an effective treatment, leading to extended life expectancy and improved quality of life. In this scenario, it is paramount to predict its need in order to allow preventive or timely administration. In this work, we propose to use itemset mining together with sequential pattern mining to unravel disease presentation patterns together with disease progression patterns by analysing, respectively, static data collected at diagnosis and longitudinal data from patient follow-up. The goal is to use these static and temporal patterns as features in prognostic models, enabling to take disease progression into account in predictions and promoting model interpretability. As case study, we predict the need for NIV within 90, 180 and 365 days (short, mid and long-term predictions). The learnt prognostic models are promising. Pattern evaluation through growth rate suggests bulbar function and phrenic nerve response amplitude, additionally to respiratory function, are significant features towards determining patient evolution. This confirms clinical knowledge regarding relevant biomarkers of disease progression towards respiratory insufficiency.

Early respiratory muscle involvement in LGMDR25: a case report

Limb girdle muscular dystrophy type R25 (LGMDR25) is a rare genetic disorder due to loss-of-function mutations in BVES, characterized by progressive proximal lower limb weakness and atrioventricular block. Here we report a young Chinese man with LGMDR25 who presented with asymmetrical lower limb weakness, myalgia, palpitations and dyspnea on exertion. Muscle imaging demonstrated fatty infiltration of the long head of biceps femoris, adductor magnus, gastrocnemius and soleus, and myoedema of semitendinosus and quadriceps, sparing rectus femoris. ECG showed only mild sinus tachycardia but pulmonary function test suggested prominent respiratory muscle weakness. Our report expands the phenotypical spectrum and indicates the importance of monitoring respiratory function in LGMDR25 patients.

S/F and ROX indices in predicting failure of high-flow nasal cannula in children

BACKGROUND

A high-flow nasal cannula (HFNC) is a useful respiratory support for children with respiratory distress; however, it elevates the risk of belated intubation. Recently, indices based on percutaneous oxygen saturation, a fraction of inspired oxygen, and respiratory rate (RR) have been suggested for the prediction of HFNC failure. We aimed to evaluate various indices predicting HFNC failure in children who started receiving HFNC at a tertiary center for 27 months.

METHODS

Cases of HFNC failure were classified as hypoxic respiratory failure (HRF) or non-HRF (NHRF) depending on the cause of intubation. The ratio of percutaneous oxygen saturation to the fraction of inspired oxygen (S/F), the ratio of S/F to RR (ROX), the ratio of S/F to RR/median RR (ROX-M), and the ratio of S/F to z-score of RR (ROX-Z) were calculated and compared between groups.

RESULTS

Of the 152 cases, 45 (29.6%) failed to wean from the HFNC support, of which 21 (46.7%) were HRFs and 24 (53.3%) were NHRFs. The S/F and ROX-M at 6 h and 3 h, respectively, predicted HRF well with a high area under the curve. Initial hypercapnia and low weight were good predictors for NHRF.

CONCLUSIONS

For the management of children with HFNC, these risk factors and indicators should be monitored to make an early decision regarding intubation.

Clinical, pathological, and molecular genetic analysis of 7 Chinese patients with hereditary myopathy with early respiratory failure

Hereditary myopathy with early respiratory failure (HMERF) is a subtype of myofibrillar myopathy. Mutations located on exon 344 of the titin-A band, the 119th fibronectin-3 domain (FN₃ 119), are responsible for HMERF. In this article, we retrospectively analyzed the clinical features, findings of muscle imaging, muscle pathology, immunohistochemistry, and ultrastructural characteristics of seven patients diagnosed with HMERF at a single center in China. Muscle MRI showed the involvement of semitendinosus in four patients. The common pathological features were variability in fiber diameter, increased internal nuclei, endomysial fibrosis, and cytoplasmic bodies. On immunohistochemical examination, the cytoplasmic bodies stained positive for calpain-3, p53, and programmed death-ligand 1. Electron microscopy showed cytoplasmic bodies, distorted sarcomere architecture, glycogen pool, and subsarcolemmal accumulation of mitochondria and lysosomes. We retrospectively reviewed four reported HMERF patients in China. Among the 11 patients, the median age at onset was 34 years (range 14-54). Allelic frequency of mutation c.95195C > T was 36.36%. This study characterizes the phenotype and genotype spectrum of HMERF in China.

Marked Respiratory Failure in an Ambulant Patient with Immune-mediated Necrotizing Myopathy and Anti-Kv1.4 and Anti-titin Antibodies

We herein report a case of seronegative immune-mediated necrotizing myopathy (IMNM) concurrent with anti-Kv1.4 and anti-titin antibodies. A 72-year-old Japanese woman presented with a 29-year history of fluctuating high serum creatine kinase (CK) levels followed by intermittent ptosis and respiratory muscle weakness. This case highlights the fact that marked respiratory muscle weakness requiring intubation can be seen in an ambulant patient with IMNM. Marked respiratory muscle weakness, rhabdomyolysis-like acute elevation of CK levels, and anti-striational muscle antibodies may be a characteristic constellation of findings in a distinct subgroup of patients with inflammatory myopathy with myasthenia gravis or similar symptoms.

Factors Influencing the Severity and Progression of Respiratory Muscle Dysfunction in Myotonic Dystrophy Type 1

Respiratory complications are the most common cause of death among patients with Myotonic Dystrophy type 1 (DM1), but the natural history of respiratory decline in DM1 patients is incompletely characterized and few predictors of the progression of respiratory dysfunction have been identified. To identify factors influencing the progression of respiratory dysfunction electronic medical records from 110 adult patients diagnosed with DM1 were reviewed along with data for respiratory symptoms and pulmonary function obtained from routine respiratory therapist clinical evaluations. At baseline, 70.9% had evidence of restrictive respiratory impairment. We examined various parameters of respiratory functional status, and found FVC (% predicted) correlated best with other measures of disease severity. Annual change in FVC was −1.42 (std error = 0.381). Greater CTG repeat size, higher MIRS rating, and longer disease duration were all correlated with lower baseline FVC but not with annual rate of change. Wide variability in clinical phenotype made determination of disease measures directly related to respiratory functional decline challenging.

Novel TNNT1 mutation and mild nemaline myopathy phenotype in an Italian patient

Mutations in the TNNT1 gene cause an infantile, lethal form of myopathy named "Amish" Nemaline Myopathy. Adult patients are very rarely described. We report a 49-year-old patient who presented a slowly progressive phenotype characterized by myalgia, exercise intolerance and dyspnea since infancy. In adult life she lapsed into a coma as a result of acute respiratory failure, with the need of tracheostomy, subsequently removed once her respiratory condition improved. Afterwards, non-invasive ventilation was started. Short stature, contractures, a small size posterior cranial fossa and osteonecrosis were additional clinical findings. Muscle MRI showed minor hypotrophy and degenerative changes of the muscles of the posterior thigh compartment and involvement of the paraspinal, medial gastrocnemius and soleus muscles with sparing of the gracilis muscle. Muscle biopsy revealed multiminicores and nemaline rods. Genetic analysis identified a new pathogenetic biallelic deletion c.786delG p.(Lys263Serfs*36) in exon 13 of TNNT1 gene. This case confirms that recessive mutations in TNNT1 gene can manifest mainly with respiratory failure in adult life.

Management of respiratory complications and rehabilitation in individuals with muscular dystrophies: 1st Consensus Conference report from UILDM - Italian Muscular Dystrophy Association (Milan, January 25-26, 2019)

Respiratory complications are common in the patient with muscular dystrophy. The periodic clinical and instrumental respiratory evaluation is extremely important. Despite the presence in the literature of updated guidelines, patient associations often report lack of knowledge of these pathologies, particularly in peripheral hospitals. The purpose of this work, inspired by the Italian Muscular Dystrophy Association (UILDM) is to improve management of respiratory problems necessary for the management of these patients complex. To this end, the main items that the specialist can meet in the follow-up of these pathologies have been analyzed and discussed, among which the respiratory basal evaluation, the criteria of adaptation to non-invasive ventilation, management of bronchial secretions, situations of respiratory emergency, indications for tracheostomy and the subject of advance directives of treatment (DAT).

Making sense of missense variants in TTN-related congenital myopathies

Mutations in the sarcomeric protein titin, encoded by TTN, are emerging as a common cause of myopathies. The diagnosis of a TTN-related myopathy is, however, often not straightforward due to clinico-pathological overlap with other myopathies and the prevalence of TTN variants in control populations. Here, we present a combined clinico-pathological, genetic and biophysical approach to the diagnosis of TTN-related myopathies and the pathogenicity ascertainment of TTN missense variants. We identified 30 patients with a primary TTN-related congenital myopathy (CM) and two truncating variants, or one truncating and one missense TTN variant, or homozygous for one TTN missense variant. We found that TTN-related myopathies show considerable overlap with other myopathies but are strongly suggested by a combination of certain clinico-pathological features. Presentation was typically at birth with the clinical course characterized by variable progression of weakness, contractures, scoliosis and respiratory symptoms but sparing of extraocular muscles. Cardiac involvement depended on the variant position. Our biophysical analyses demonstrated that missense mutations associated with CMs are strongly destabilizing and exert their effect when expressed on a truncating background or in homozygosity. We hypothesise that destabilizing TTN missense mutations phenocopy truncating variants and are a key pathogenic feature of recessive titinopathies that might be amenable to therapeutic intervention.

Predictors of respiratory decline in myotonic dystrophy type 1 (DM1): a longitudinal cohort study

We studied 33 patients affected by juvenile and adult myotonic dystrophy type 1 (DM1). The aim of the study was to assess clinical and laboratory parameters that could predict the requirement of noninvasive ventilation (NIV) in DM1. Secondary outcome was to assess the interplay between genetic profile, muscle impairment severity and presence of cardiac comorbidities.Patients with genetic diagnosis of DM1 were recruited. An abnormal trinucleotide repeat (CTG) expansion of dystrophy protein kinase gene (DMPK) on chromosome 19q13.3 was the prerequisite for inclusion. The number of triplet repeats was measured in genomic DNA to classify subjects. A multidisciplinary team evaluated the patients every 6-8 months up to 18 years with serial cardiological and respiratory function assessments. Neurological progression was monitored using a validated DM1-specific rating scale (MIRS). Independent variables considered for the study outcomes were gender, genetic status, age of presentation, MIRS scores, and results of pulmonary function tests (PFTs).Patients were 17 males (51.5%) and 16 females (48.5%). 16 cases were younger than mean age of 31.4 years, the remaining 17 were up to 65. 12 subjects (36.4%) underwent NIV during follow up. Cardiac comorbidities were detected in 63.6% of cases and in 91% of patients in NIV. Among PFTs, forced vital capacity (FVC) was a reliable indicator of respiratory decline. FVC values were significantly associated with clinical muscle severity assessed by MIRS.Severity of muscular impairment, CTG expansion size, age and presence of cardiac comorbidities predict respiratory impairment in DM1.

Titinopathy, an atypical respiratory failure

Hereditary myopathy with early respiratory failure is a neuromuscular disease with an autosomal dominant inheritance pattern. Clinical presentation is characterised by proximal and distal muscle weakness, exertional dyspnoea and generalised fatigue. There is no disease-modifying therapy and the prognosis is unknown. Herein we present a case of a 40-year-old woman with long-standing asthenia and apathy and, more recently, daytime sleepiness, dyspnoea and difficulty in walking. A hypercapnic respiratory failure with severe acidemia was identified. The muscle biopsy showed the presence of cytoplasmatic bodies and rimmed vacuoles, suggestive of a hereditary myopathy with early respiratory failure disease. The genetic study confirmed this diagnosis identifying a heterozygous mutation on c.95134T>C (p.Cys31712Arg) in exon 343 in the titin gene. The patient was discharged home under supportive treatment with non-invasive ventilation.

Predictors of prognosis in type 1 myotonic dystrophy (DM1): longitudinal 18-years experience from a single center

The aim of the study was to identify possible predictors of neurological worsening and need of non-invasive ventilation (NIV) in individuals affected by myotonic dystrophy type 1 (DM1), the most common form of adult-onset muscular dystrophy.

METHODS

A retrospective observational cohort study was undertaken. Thirty-three patients with genetic diagnosis of DM1 were followed at our Neuromuscular unit in Modena. Abnormal trinucleotide repeat (CTG) expansion of dystrophy protein kinase gene (MDPK) on chromosome 19q 13.3 was the prerequisite for inclusion. The number of CTG repeats was determined. All the participants were older than 14 at the time of enrolment, therefore they could be included into the juvenile or adult form of the disease. Participants were neurologically evaluated every 6-8 months up to 18 years. Neurological impairment was assessed by Muscular Impairment Rating (MIRS), Medical Research Council (MRC), and modified Rankin (mRS) scales. The independent variables considered for prognosis were age at first evaluation, duration of the disease, CTG repeat number, gender, and presence of cardiac and vascular morbidities.Male patients were 51.5% and female patients 48.5%. Sixteen patients were younger than the mean age of 30.1 years, while the remaining 17 were up to 65. Twelve subjects (36.4%) underwent NIV before the end of follow-up. Muscle force and disability scores showed statistically significant deterioration (p < 0.001) during follow-up. The worsening was significantly higher among patients carrying higher number of CTG repeats and of younger age. The presence of cardio-vascular involvement has significant impact on neurological and respiratory progression.Neurological worsening is predicted by CTG expansion size, young age and presence of cardio-vascular morbidities.

Signs and Symptoms in Congenital Myopathies

Congenital myopathies (CM) represent a continuously growing group of disorders with a wide range of clinical and histopathologic presentations. The refinement and application of new technologies for genetic diagnosis have broadened our understanding of the genetic causes of CM. Our growing knowledge has revealed that there are no clear limits between each subgroup of CM, and thus the clinical overlap between genes has become more evident. The implementation of next generation sequencing has produced vast amounts of genomic data that may be difficult to interpret. With an increasing number of reports revealing variants of unknown significance, it is essential to support the genetic diagnosis with a well characterized clinical description of the patient. Phenotype-genotype correlation should be a priority at the moment of disclosing the genetic results. Thus, a detailed physical examination can provide us with subtle differences that are not only key in order to arrive at a correct diagnosis, but also in the characterization of new myopathies and candidate genes.

Expanding the importance of HMERF titinopathy: new mutations and clinical aspects

Objective

Hereditary myopathy with early respiratory failure (HMERF) is caused by titin A-band mutations in exon 344 and considered quite rare. Respiratory insufficiency is an early symptom. A collection of families and patients with muscle disease suggestive of HMERF was clinically and genetically studied.

Methods

Altogether 12 new families with 19 affected patients and diverse nationalities were studied. Most of the patients were investigated using targeted next-generation sequencing; Sanger sequencing was applied in some of the patients and available family members. Histological data and muscle MRI findings were evaluated.

Results

Three families had several family members studied while the rest were single patients. Most patients had distal and proximal muscle weakness together with respiratory insufficiency. Five heterozygous TTN A-band mutations were identified of which two were novel. Also with the novel mutations the muscle pathology and imaging findings were compatible with the previous reports of HMERF.

Conclusions

Our collection of 12 new families expands mutational spectrum with two new mutations identified. HMERF is not that rare and can be found worldwide, but maybe underdiagnosed. Diagnostic process seems to be complex as this study shows with mostly single patients without clear dominant family history.

Identification of novel target genes in human lung tissue involved in chronic obstructive pulmonary disease

Introduction

As part of a study aimed at illuminating at least some of the complex molecular events taking place in COPD, we screened tissues by means of transcriptome analyses.

Materials and methods

Tissues were subjected to transcriptome analysis. Candidate genes were identified and validated by immunohistochemistry. Primary human lung cells were subjected to stimulation with cigarette smoke extract for further validation by real time PCR.

Results

Six candidate genes were selected for further investigations: Aquaporin 3 (AQP3), extracellular matrix protein 1 (ECM1), four and a half LIM domain 1 (FHL1), milk fat globule epidermal growth factor 8 (MFGE8, lactadherin), phosphodiesterase 4D-interacting protein (PDE4DIP), and creatine transporter SLC6A8. All six proteins were allocated to distinct cell types by immunohistochemistry. Upon stimulation with cigarette smoke extract, human type II pneumocytes showed a dose-dependent down-regulation of MFGE8, while ECM1 and FHL1 also tended to be down-regulated. Although present, none of the candidates was regulated by cigarette smoke extract in primary human macrophages.

Discussion

MFGE8 turned out to be an interesting new candidate gene in COPD deserving further studies.

Respiratory involvement in neuromuscular disorders

PURPOSE OF REVIEW

In numerous neuromuscular disorders (NMDs), respiratory muscle weakness is present, and acute or chronic respiratory failure may evolve. Very often, respiratory involvement substantially adds to the burden of disease, impairs quality of life, or reduces life expectancy. This article summarizes new aspects of both diagnosis and management of respiratory muscle weakness in patients with NMDs.

RECENT FINDINGS

Drugs like deflazacort, ataluren, eteplirsen, and nusinersen are now approved treatments for Duchenne Muscular Dystrophy and Spinal Muscular Atrophy, and others are on their way in NMDs. Although observing how innovative drugs will change the natural history of these diseases, including respiratory function over time, adequate symptomatic treatment remains meaningful and is strongly recommended. Physicians should systematically take respiratory involvement into account to improve patients' quality of life and prognosis.

SUMMARY

First, it is outlined in which subtypes of NMD respiratory muscle dysfunction is particularly relevant. Second, new developments regarding diagnostic procedures, including respiratory muscle strength testing, spirometry, and sleep studies, are covered. Third, this article gives an overview on current concepts of ventilatory support and management of secretions in patients with NMD.

Respiratory failure because of neuromuscular disease

PURPOSE OF REVIEW

Understanding the mechanisms and abnormalities of respiratory function in neuromuscular disease is critical to supporting the patient and maintaining ventilation in the face of acute or chronic progressive impairment.

RECENT FINDINGS

Retrospective clinical studies reviewing the care of patients with Guillain-Barré syndrome and myasthenia have shown a disturbingly high mortality following step-down from intensive care. This implies high dependency and rehabilitation management is failing despite evidence that delayed improvement can occur with long-term care. A variety of mechanisms of phrenic nerve impairment have been recognized with newer investigation techniques, including EMG and ultrasound. Specific treatment for progressive neuromuscular and muscle disease has been increasingly possible particularly for the treatment of myasthenia, metabolic myopathies, and Duchenne muscular dystrophy. For those conditions without specific treatment, it has been increasingly possible to support ventilation in the domiciliary setting with newer techniques of noninvasive ventilation and better airway clearance. There remained several areas of vigorous debates, including the role for tracheostomy care and the place of respiratory muscle training and phrenic nerve/diaphragm pacing.

SUMMARY

Recent studies and systematic reviews have defined criteria for anticipating, recognizing, and managing ventilatory failure because of acute neuromuscular disease. The care of patients requiring long-term noninvasive ventilatory support for chronic disorders has also evolved. This has resulted in significantly improved survival for patients requiring domiciliary ventilatory support.

Prevalence of adult Pompe disease in patients with proximal myopathic syndrome and undiagnosed muscle biopsy

We examined patients with limb-girdle muscle weakness and/or hyper-CKaemia and undiagnosed muscle biopsy for late onset Pompe disease (LOPD). Patients with an inconclusive limb-girdle muscle weakness who presented at our neuromuscular centre between 2005 and 2015 with undiagnosed muscle biopsies were examined by dry blood spot testing (DBS) including determination of the enzyme activity of acid alpha-glucosidase (GAA). In the case of depressed enzyme activity, additional gene testing of the GAA gene was carried out. Of the 340 evaluated muscle biopsies, 69 patients fulfilled the inclusion criteria and were examined with DBS. Among those patients, 76% showed a limb-girdle muscle weakness and 14% showed a hyper-CKaemia. A diagnosis of LOPD could be established in the case of two patients (2.9%) with reduced GAA enzyme activity and proof of mutations in the GAA gene. One of the two patients presents in the muscle biopsy suggestive features of Pompe disease including vacuoles with positive acid phosphatase reaction. In summary, our results show that a muscle biopsy can be helpful in identifying LOPD patients, but vacuolation with glycogen storage can also be absent. An inconspicuous muscle biopsy does not rule out Pompe disease. Consequently, all patients with limb-girdle muscle weakness should be examined by DBS before conducting a muscle biopsy.

TITINdb-a computational tool to assess titin's role as a disease gene

SUMMARY

Large numbers of rare and unique titin missense variants have been discovered in both healthy and disease cohorts, thus the correct classification of variants as pathogenic or non-pathogenic has become imperative. Due to titin's large size (363 coding exons), current web applications are unable to map titin variants to domain structures. Here, we present a web application, TITINdb, which integrates titin structure, variant, sequence and isoform information, along with pre-computed predictions of the impact of non-synonymous single nucleotide variants, to facilitate the correct classification of titin variants.

AVAILABILITY AND IMPLEMENTATION

TITINdb can be freely accessed at http://fraternalilab.kcl.ac.uk/TITINdb.

CONTACT

franca.fraternali@kcl.ac.uk.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Clinical Features, Molecular Heterogeneity, and Prognostic Implications in YARS2-Related Mitochondrial Myopathy

Importance

YARS2 mutations have been associated with a clinical triad of myopathy, lactic acidosis, and sideroblastic anemia in predominantly Middle Eastern populations. However, the identification of new patients expands the clinical and molecular spectrum of mitochondrial disorders.

Objectives

To review the clinical, molecular, and genetic features of YARS2-related mitochondrial disease and to demonstrate a new Scottish founder variant.

Design, Setting, and Participants

An observational case series study was conducted at a national diagnostic center for mitochondrial disease in Newcastle upon Tyne, England, and review of cases published in the literature. Six adults in a well-defined mitochondrial disease cohort and 11 additional cases described in the literature were identified with YARS2 variants between January 1, 2000, and January 31, 2015.

Main Outcome and Measures

The spectrum of clinical features and disease progression in unreported and reported patients with pathogenic YARS2 variants.

Results

Seventeen patients (median [interquartile range] age at onset, 1.5 [9.8] years) with YARS2-related mitochondrial myopathy were identified. Fifteen individuals (88%) exhibited an elevated blood lactate level accompanied by generalized myopathy; only 12 patients (71%) manifested with sideroblastic anemia. Hypertrophic cardiomyopathy (9 [53%]) and respiratory insufficiency (8 [47%]) were also prominent clinical features. Central nervous system involvement was rare. Muscle studies showed global cytochrome-c oxidase deficiency in all patients tested and severe, combined respiratory chain complex activity deficiencies. Microsatellite genotyping demonstrated a common founder effect shared between 3 Scottish patients with a p.Leu392Ser variant. Immunoblotting from fibroblasts and myoblasts of an affected Scottish patient showed normal YARS2 protein levels and mild respiratory chain complex defects. Yeast modeling of novel missense YARS2 variants closely correlated with the severity of clinical phenotypes.

Conclusions and Relevance

The p.Leu392Ser variant is likely a newly identified founder YARS2 mutation. Testing for pathogenic YARS2 variants should be considered in patients presenting with mitochondrial myopathy, characterized by exercise intolerance and muscle weakness even in the absence of sideroblastic anemia irrespective of ethnicity. Regular surveillance and early treatment for cardiomyopathy and respiratory muscle weakness is advocated because early treatment may mitigate the significant morbidity and mortality associated with this genetic disorder.

Prevalence of late-onset pompe disease in Portuguese patients with diaphragmatic paralysis - DIPPER study

Pompe disease is a rare autosomal recessive neuromuscular disorder caused by acid α-glucosidase enzyme (GAA) deficiency and divided into two distinct variants, infantile- and late-onset. The late-onset variant is characterized by a spectrum of phenotypic variation that may range from asymptomatic, to reduced muscle strength and/or diaphragmatic paralysis. Since muscle strength loss is characteristic of several different conditions, which may also cause diaphragmatic paralysis, a protocol was created to search for the diagnosis of Pompe disease and exclude other possible causes.

METHODS

We collected a sample size of 18 patients (10 females, 8 males) with a median age of 60 years and diagnosis of diaphragmatic paralysis of unknown etiology, followed in the Pulmonology outpatient consultation of 9 centers in Portugal, over a 24-month study period. We evaluated data from patient's clinical and demographic characteristics as well as complementary diagnostic tests including blood tests, imaging, neurophysiologic and respiratory function evaluation. All patients were evaluated for GAA activity with DBS (dried blood test) or serum quantification and positive results confirmed by serum quantification and sequencing.

RESULTS

Three patients were diagnosed with Pompe's disease and recommended for enzyme replacement therapy. The prevalence of Pompe, a rare disease, in our diaphragmatic paralysis patient sample was 16.8%.

CONCLUSION

We conclude that DBS test for GAA activity should be recommended for all patients with diaphragmatic paralysis which, despite looking at all the most common causes, remains of unknown etiology; this would improve both the timing and accuracy of diagnosis for Pompe disease in this patient population. Accurate diagnosis will lead to improved care for this rare, progressively debilitating but treatable neuromuscular disease.

Recent advances in amyotrophic lateral sclerosis

ALS is a relentlessly progressive and fatal disease, with no curative therapies available to date. Symptomatic and palliative care, provided in a multidisciplinary context, still remains the cornerstone of ALS management. However, our understanding of the molecular mechanisms underlying the disease has advanced greatly over the past years, giving new hope for the development of novel diagnostic and therapeutic approaches. Here, we have reviewed the most recent studies that have contributed to improving both clinical management and our understanding of ALS pathogenesis.

BAG3: a new player in the heart failure paradigm

BAG3 is a cellular protein that is expressed predominantly in skeletal and cardiac muscle but can also be found in the brain and in the peripheral nervous system. BAG3 functions in the cell include: serving as a co-chaperone with members of the heat-shock protein family of proteins to facilitate the removal of misfolded and degraded proteins, inhibiting apoptosis by interacting with Bcl2 and maintaining the structural integrity of the Z-disk in muscle by binding with CapZ. The importance of BAG3 in the homeostasis of myocytes and its role in the development of heart failure was evidenced by the finding that single allelic mutations in BAG3 were associated with familial dilated cardiomyopathy. Furthermore, significant decreases in the level of BAG3 have been found in end-stage failing human heart and in animal models of heart failure including mice with heart failure secondary to trans-aortic banding and in pigs after myocardial infarction. Thus, it becomes relevant to understand the cellular biology and molecular regulation of BAG3 expression in order to design new therapies for the treatment of patients with both hereditary and non-hereditary forms of dilated cardiomyopathy.

[Non-cardiac and non-pulmonary causes of dyspnea]

In addition to cardiac and pulmonary diseases there is a broad variety of different underlying causes of dyspnea. The spectrum includes the different forms of anemia, all causes of upper airway obstructions, neuromuscular diseases and psychopathological disorders. This article gives a brief review of the entire spectrum by providing information about differential diagnostics as well as the main therapeutic principles. A field of growing interest is dyspnea in the context of palliative care.

A comprehensive review of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset fatal neurodegenerative disease affecting motor neurons with an incidence of about 1/100,000. Most ALS cases are sporadic, but 5–10% of the cases are familial ALS. Both sporadic and familial ALS (FALS) are associated with degeneration of cortical and spinal motor neurons. The etiology of ALS remains unknown. However, mutations of superoxide dismutase 1 have been known as the most common cause of FALS. In this study, we provide a comprehensive review of ALS. We cover all aspects of the disease including epidemiology, comorbidities, environmental risk factor, molecular mechanism, genetic factors, symptoms, diagnostic, treatment, and even the available supplement and management of ALS. This will provide the reader with an advantage of receiving a broad range of information about the disease.