A rare TNNT1 gene variant causing creatine kinase elevation in nemaline myopathy: c.271_273del (p.Lys91del).

BACKGROUND: Nemaline Myopathy (NM) is a rare genetic disorder that affects muscle function and is characterized by the presence of nemaline rods in muscle fibers. These rods are abnormal structures that interfere with muscle contraction and can cause muscle weakness, respiratory distress, and other complications. NM is caused by variants in several genes, including TNNT1, which encodes the protein troponin T1. NM is inherited in an autosomal recessive pattern. The prevalence of heterozygous TNNT1 variants has been reported to be 1/152,000, indicating that the disease is relatively rare. OBJECTIVE: Investigation of TNNT1 gene variants that may cause cretin kinase elevation. METHODS: Detailed family histories and clinical data were recorded. Whole exome sequencing was performed and family segregation was done by Sanger sequencing. RESULTS: In this study, we report a 5-year-old girl with a novel variant recessive congenital TNNT1 myopathy. The patient had a novel homozygous (c.271_273del) deletion in the TNNT1 gene that is associated with creatine kinase elevation, which is a marker of muscle damage. CONCLUSION: This case expands the phenotypic spectrum of TNNT1 myopathy and highlights the importance of genetic testing and counseling for families affected by this rare disorder. In this study provides valuable insights into the genetic basis of NM and highlights the importance of early diagnosis and management for patients with this rare disorder. Further research is needed to better understand the pathophysiology of TNNT1 myopathy and to develop effective treatments for this debilitating condition.

Anesthetic management for surgery in a nemaline myopathy patient with difficult airway: A CARE-compliant case report.

RATIONALE: Nemaline myopathy (NM) is a congenital disease characterized by nonprogressive or slowly progressing muscle weakness and may increase the risk of anesthesia in case of respiratory muscle or cardiac involvement. Care should be taken to prevent respiratory failure after surgery. PATIENT CONCERNS: A 35-year-old man with NM, who had difficult airway, restrictive ventilatory pattern, and pulmonary hypertension, required general anesthesia for surgery because of limited mouth opening. DIAGNOSES: The patient was diagnosed with NM (ACTA1 mutation) and coronoid hyperplasia. INTERVENTIONS: Awake fiberoptic nasal intubation was performed following preparations for analgesia. General anesthesia was maintained using inhalational anesthetics and opioids without using neuromuscular blocking agents. OUTCOMES: General anesthesia remained well maintained during surgery, with no movement or spontaneous breathing of the patient and he recovered from anesthesia uneventfully without complications. LESSONS: This report highlights the safe performance of anesthesia induction and recovery in a case where anesthesia management is necessary for surgery in a patient of NM at a high risk of anesthesia-related complications.

Sporadic Late-Onset Nemaline Myopathy: Current Landscape.

PURPOSE OF REVIEW: Sporadic late-onset nemaline myopathy (SLONM) is a rare adult-onset, acquired, muscle disease that can be associated with monoclonal gammopathy or HIV infection. The pathological hallmark of SLONM is the accumulation of nemaline rods in muscle fibers. We review here current knowledge about its presentation, pathophysiology, and management. RECENT FINDINGS: SLONM usually manifests with subacutely progressive proximal and axial weakness, but it can also present with chronic progressive weakness mimicking muscular dystrophy. The pathophysiology of the disease remains poorly understood, with evidence pointing to both autoimmune mechanisms and hematological neoplasia. Recent studies have identified histological, proteomic, and transcriptomic alterations that shed light on disease mechanisms and distinguish SLONM from inherited nemaline myopathies. A majority of SLONM patients respond to intravenous immunoglobulins, chemotherapy, or hematopoietic stem cell transplant. SLONM is a treatable myopathy, although its underlying etiology and pathomechanisms remain unclear. A high degree of suspicion should be maintained for this disease to reduce diagnostic delay and treatment in SLONM and facilitate its distinction from inherited nemaline myopathies.

Nemaline myopathy: reclassification of previously reported variants according to ACMG guidelines, and report of novel genetic variants.

Nemaline myopathy (NM) is a heterogeneous genetic neuromuscular disorder characterized by rod bodies in muscle fibers resulting in multiple complications due to muscle weakness. NM patients and their families could benefit from genetic analysis for early diagnosis, carrier and prenatal testing; however, clinical classification of variants is subject to change as further information becomes available. Reclassification can significantly alter the clinical management of patients and their families. We used the newly published data and ACMG/AMP guidelines to reassess NM-associated variants previously reported by clinical laboratories (ClinVar). Our analyses on rare variants that were not canonical loss-of-function (LOF) resulted in the downgrading of ~29% (28/97) of variants from pathogenic or likely-pathogenic (P/LP) to variants of uncertain significance (VUS). In addition, we analyzed the splicing effect of variants identified in NM patients by clinical laboratories or research, using an accurate in silico prediction tool that applies a deep-learning network. We identified 55 rare variants that may impact splicing (cryptic splicing). We also analyzed six new NM families and identified eight variants in NEB and ACTA1, including three novel variants: homozygous pathogenic c.164A > G (p.Tyr55Cys), and homozygous likely pathogenic c.980T > C (p.Met327Thr) in ACTA1, and heterozygous VUS c.18694-3T > G in NEB. This study demonstrates the importance of reclassifying variants to facilitate more definitive "calls" on causality or no causality in clinical genetic testing of patients with NM. Reclassification of ~150 variants is now available for improved clinical management, risk counseling and screening of NM patients.

Sporadic late onset nemaline myopathy with concurrent dermatological symptoms responding to immunosuppressive treatment.

BACKGROUND: Sporadic late onset nemaline myopathy is a rare, progressive muscle disease, presenting in adulthood, mainly affecting proximal limb and bulbar muscles. Muscle biopsies show characteristic nemaline rods. The putative mechanism is considered immune-related. Other manifestations aside from neuromuscular symptoms have not been described previously. CASE PRESENTATION: We present a case with atypical sporadic late onset nemaline myopathy (SLONM) of a non-HIV, non-MGUS subtype, where skin manifestations preceded neuromuscular symptoms, and a residual thymus with the histology of thymic follicular hyperplasia was detected during the diagnostic workup. Thorough dermatological investigations could not explain the skin presentations. Muscle biopsy revealed variation in fiber diameter, ragged-red and COX-negative fibers associated with discrete fibrosis. Electron microscopy detected atrophic muscle fibres with disorganization of the myofibrils, nemaline rods and abnormal mitochondria. Single-fiber EMG suggested signs of a neuromuscular transmission defect, EMG showed signs of myopathy. Analyses of antibodies associated with myasthenia gravis were negative. The patient showed improvement after intravenous immunoglobulin treatment regarding both the skin and the muscle symptoms. CONCLUSIONS: Our case highlights the heterogeneity of SLONM with its varied spectrum of presentation. A unique combination of dermatological symptoms and SLONM could be seen with skin lesions as primary presenting symptoms. An association can be considered between the different manifestations, presumably based on immune etiology, where immunosuppressive therapy has been beneficial.

Nemaline myopathy in a six-month-old Pomeranian dog.

ABSTRACT: Nemaline myopathy - a clinically and genetically complex heterogenous group of disorders - is described uncommonly in humans and rarely in animals, and is characterised by progressive muscle weakness. The diagnosis is confirmed by histological and/or ultrastructural identification of subsarcolemmal, thread-like, rod-shaped structures called nemaline rod bodies within more than 40% of skeletal muscle fibres. These rods contain the Z-line protein, α-actinin, that can be effectively stained in skeletal muscles using Gomori or Masson trichrome and negatively stained with periodic acid-Schiff. Similar rod-like bodies have been found in smaller numbers in dogs with endocrine disorders and occasionally in other conditions in humans. This report is of a six-monthold Pomeranian dog which had progressive exercise intolerance over a two-month period associated with severe disuse muscle atrophy of the thoracic limbs, as well as gradual pelvic limb weakness and regurgitation of food. Baseline diagnostics ruled out endocrinopathies and after histological and ultrastructural evaluation of thoracic limb muscles and nerve biopsies confirmed nemaline myopathy. The clinical course, diagnostic test results, ultrastructure of skeletal muscle and peripheral nerve, gross necropsy findings and histopathology using various stains are described and illustrated.

Clinicopathologic Profiles of Sporadic Late-Onset Nemaline Myopathy: Practical Importance of Anti-α-Actinin Immunostaining.

BACKGROUND AND OBJECTIVES: Sporadic late-onset nemaline myopathy (SLONM) is a treatable or otherwise fatal myopathy. Diagnosis of SLONM is still challenging, and no therapeutic consensus has been achieved. Here, we reported the clinicopathologic features and long-term follow-up data of SLONM in a Chinese cohort. METHODS: We performed a retrospective evaluation of clinical, pathologic, and treatment outcomes of 17 patients with SLONM diagnosed between March 1986 and April 2021 at our neuromuscular center. Immunohistochemistry (IHC) with antibodies against 5 Z-disc-associated proteins was performed in the muscle biopsies of SLONM to identify a potential pathologic marker in aid of diagnosis. In comparison, we also performed muscle IHC in patients with selective type II fiber atrophy (n = 22), neurogenic atrophy (n = 22), mitochondrial myopathy (n = 5), immune-mediated necrotizing myopathy (n = 5), and normal controls (n = 5). RESULTS: Most of the patients exhibited asymmetric limb muscles weakness (71%, 12/17) and neck extensor weakness (53%, 9/17). Immunofixation electrophoresis was performed in 11 patients, and 4 of them were identified with monoclonal gammopathy of undetermined significance (MGUS). EMG from 16 patients demonstrated a myopathic pattern with spontaneous activities in 69% (11/16) of them. Muscle MRI showed preferential involvement of paraspinal, gluteus minimus and medius, semimembranosus, and soleus muscles. Suspected nemaline bodies on modified Gomori trichrome were confirmed by IHC using anti-α-actinin antibody (100%, 17/17), anti-myotilin antibody (94%, 16/17), anti-desmin antibody (94%, 16/17), anti-α-B crystallin antibody (65%, 11/17), and anti-telethonin antibody (18%, 3/17) with various positive rates. Notably, anti-α-actinin IHC showed the highest percentage of strongly positive staining (77%, 13/17), being the only one without negative results. Moderate improvement following autologous stem cell transplantation (ASCT) was noted in 3/4 patients with MGUS; favorable outcomes were also achieved in 6/7 patients without MGUS, including 3 patients with complete recovery who were given a combined treatment of prednisone and another immunosuppressant. DISCUSSION: SLONM is a treatable myopathy with ASCT or traditional immunotherapy, especially when combined with steroids and immunosuppressants. Anti-α-actinin immunostaining is the most reliable pathologic marker to identify rod-bearing fibers, and it should be performed routinely in adult patients with undiagnosed nonnecrotic myopathies.

Coexisting sporadic late onset nemaline myopathy and AL amyloid myopathy - incidental or related?

Sporadic late onset nemaline myopathy (SLONM) and amyloid myopathy are frequently unrecognized acquired and treatable myopathies, which classically present with rapidly progressive and severe proximal muscle weakness. We report a case of SLONM and amyloid myopathy associated with IgM lambda monoclonal gammopathy in a 77-year-old Caucasian man. Creatine kinase (CK) was mildly elevated. Myositis panel was negative. Electromyogram showed prominent fibrillation potentials and positive sharp waves with myopathic motor unit action potentials. Muscle biopsy revealed nemaline rods and amyloid deposits with characteristic apple-green birefringence under polarized light, and liquid chromatography tandem mass spectroscopy detected a peptide profile consistent with AL (lambda) type amyloid deposition. Genetic testing for congenital nemaline rod myopathy was negative. The patient was treated with dexamethasone and chemotherapy x3 cycles with very good partial remission. CK and lambda light chain normalized. Our case emphasizes the importance of completing a thorough histochemical and pathological evaluation by muscle biopsy analysis, to provide timely and optimal treatment of these conditions.

68-year old man with progressive weakness and ventilator dependent respiratory failure: a case report of sporadic late onset nemaline myopathy.

BACKGROUND: Neuromuscular pathologies must be considered when caring for patients with persistent or progressive respiratory failure. Pertinent disease states may involve skeletal muscles of respiration or associated neurologic structures including motor neurons, peripheral neurons and the neuromuscular junction. Diagnosis may require pulmonary function testing, neurophysiologic studies, imaging, and/or muscle biopsy. CASE PRESENTATION: A 68-year-old male was transferred to our intensive care unit (ICU) for management of ventilator dependent respiratory failure. Upon further historical review, he described gradually worsening gait instability and muscle weakness, which was previously attributed to vascular Parkinsonism in the setting of known cerebrovascular disease. Upon arrival to our hospital, he was found to have elevated muscle specific enzymes, prompting evaluation for neuromuscular causes of respiratory failure. He was also found to have elevated HMG-CoA Reductase (HMGCR) antibodies. Ultimately, a right quadriceps muscle biopsy was performed and electron microscopy identified nemaline bodies within skeletal myofibers. Given the clinical course and other histopathologic findings, he was diagnosed with Sporadic late-onset nemaline myopathy (SLONM). CONCLUSION: The diagnosis of neuromuscular disease in patients with ventilator dependent respiratory failure is challenging. A detailed history of a patient's clinical course prior to hospitalization is key and may raise suspicion for underlying neuromuscular pathology. Further evaluation in non-critically ill patients may include pulmonary function, electromyography and confirmatory muscle biopsy. Sporadic late onset nemaline myopathy remains a rare disease entity which rarely presents with respiratory failure and lacks effective treatment.

Nemaline Myopathy Initially Diagnosed as Right Heart Failure with Type 2 Respiratory Failure.

Nemaline myopathy (NM) is a rare muscle disease with various clinical types. In some cases, NM can lead to type 2 respiratory failure and right heart failure. We herein report a patient with congenital NM with nebulin gene mutation who presented with acute right heart failure and type 2 respiratory failure due to respiratory muscle paralysis after upper respiratory tract infection, needing a permanent ventilator for assistance. However, the limb and trunk muscle strengths were within normal limits. This case showed that NM should be considered as a cause of right heart failure and type 2 respiratory failure.

A homozygous CAP2 pathogenic variant in a neonate presenting with rapidly progressive cardiomyopathy and nemaline rods.

Nemaline Myopathy (NM) is a disorder of skeletal muscles caused by mutations in sarcomere proteins and characterized by accumulation of microscopic rod or thread-like structures (nemaline bodies) in skeletal muscles. Patients diagnosed with both NM and infantile cardiomyopathy are very rare. A male infant presented, within the first few hours of life, with severe dilated cardiomyopathy, biventricular dysfunction and left ventricular noncompaction. A muscle biopsy on the 8th day of life from the right sternocleidomastoid muscle identified nemaline rods. Whole exome sequencing identified a c.1288 delT (homozygous pathogenic variant) in the CAP2 gene (NM_006366), yielding a CAP2 protein (NP_006357.1) with a p.C430fs. Both parents were heterozygous for the same variant but have no history of heart or muscle disease. Analysis of patient derived fibroblasts and cardiomyocytes derived from induced pluripotent stem cells confirmed the p.C430fs mutation (pathogenic variant), which appears to cause loss of both CAP2 protein and mRNA. The CAP2 gene encodes cyclase associated protein 2, an actin monomer binding and filament depolymerizing protein and CAP2 knockout mice develop severe dilated cardiomyopathy and muscle weakness. The patient underwent a heart transplant at 1 year of age. Heart tissue explanted at that time also showed nemaline rods and additionally disintegration of the myofibrillar structure. Other extra cardiac concerns include mild hypotonia, atrophic and widened scarring. This is the first description of a patient presenting with nemaline myopathy associated with a pathogenic variant of CAP2.

Pediatric Nemaline Myopathy: A Systematic Review Using Individual Patient Data.

Nemaline myopathy is a skeletal muscle disease that affects 1 in 50 000 live births. The objective of this study was to develop a narrative synthesis of the findings of a systematic review of the latest case descriptions of patients with NM. A systematic search of MEDLINE, Embase, CINAHL, Web of Science, and Scopus was performed using Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines using the keywords pediatric, child, NM, nemaline rod, and rod myopathy. Case studies focused on pediatric NM and published in English between January 1, 2010, and December 31, 2020, in order to represent the most recent findings. Information was collected about the age of first signs, earliest presenting neuromuscular signs and symptoms, systems affected, progression, death, pathologic description, and genetic changes. Of a total of 385 records, 55 case reports or series were reviewed, covering 101 pediatric patients from 23 countries. We review varying presentations in children ranging in severity despite being caused by the same mutation, in addition to current and future clinical considerations relevant to the care of patients with NM. This review synthesizes genetic, histopathologic, and disease presentation findings from pediatric NM case reports. These data strengthen our understanding of the wide spectrum of disease seen in NM. Future studies are needed to identify the underlying molecular mechanism of pathology, to improve diagnostics, and to develop better methods to improve the quality of life for these patients.

Fetal akinesia: The need for clinical vigilance in first trimester with decreased fetal movements.

OBJECTIVE: We present two cases of fetal akinesia detected by first trimester ultrasound with noticing reduced fetal movements. CASE REPORT: Both of the two cases presented with reduced fetal movements. Fetal microarray results were normal. Follow-up sonographic examinations showed that Case 1 had structural anomalies with reduced fetal movements, and Case 2 had findings of reduced fetal movements and olyhydramnios. Case 1 ended with termination of pregnancy, and was confirmed to suffer from distal arthrogryposis (DA) type 5D (DA5D) with two pathogenic ECEL1 variants, NM_004826: c.110_155del46 (p.F37Cfs∗151) and c.633G > C (p.W211C). Case 2 continued to term. However, the infant developed breathing problems and severe hypotonia after birth, and died at 3 months. Nemaline myopathy was diagnosed with two NEB variants, NM_001271208.1: c.3255+1G > T and c.7165delA (p.W211C) detected in the patient. CONCLUSION: The first trimester ultrasound can detect clues that lead to the diagnosis of fetal akinesias presenting with reduced or absent fetal movements. Our results would be useful in counselling parents of affected pregnancies and in alerting physicians to plan the appropriate follow-up investigations for such cases.

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.

Noteworthy Cardiovascular Involvement with Sporadic Late-onset Nemaline Myopathy.

Cardiac involvement has recently been the focus of sporadic late-onset nemaline myopathy (SLONM). However, right ventricular failure and pulmonary hypertension, in addition to repetitive cardiac arrest, are noteworthy characteristics of SLONM. We herein report a 66-year-old woman with SLONM whose main symptoms were cardiac arrest, right ventricular failure, and pulmonary hypertension. Despite permanent pacemaker replacement, cardiac arrest occurred repetitively, and even with continuous positive airway pressure, right ventricular failure and pulmonary hypertension persisted. The patient was finally diagnosed with SLONM by a muscle biopsy. Our case suggests the possibility of cardiovascular involvement in SLONM, especially right ventricular failure and pulmonary hypertension.

Clinical phenotype and loss of the slow skeletal muscle troponin T in three new patients with recessive TNNT1 nemaline myopathy.

BACKGROUND: Congenital nemaline myopathies are rare pathologies characterised by muscle weakness and rod-shaped inclusions in the muscle fibres. METHODS: Using next-generation sequencing, we identified three patients with pathogenic variants in the Troponin T type 1 (TNNT1) gene, coding for the troponin T (TNT) skeletal muscle isoform. RESULTS: The clinical phenotype was similar in all patients, associating hypotonia, orthopaedic deformities and progressive chronic respiratory failure, leading to early death. The anatomopathological phenotype was characterised by a disproportion in the muscle fibre size, endomysial fibrosis and nemaline rods. Molecular analyses of TNNT1 revealed a homozygous deletion of exons 8 and 9 in patient 1; a heterozygous nonsense mutation in exon 9 and retention of part of intron 4 in muscle transcripts in patient 2; and a homozygous, very early nonsense mutation in patient 3.Western blot analyses confirmed the absence of the TNT protein resulting from these mutations. DISCUSSION: The clinical and anatomopathological presentations of our patients reinforce the homogeneous character of the phenotype associated with recessive TNNT1 mutations. Previous studies revealed an impact of recessive variants on the tropomyosin-binding affinity of TNT. We report in our patients a complete loss of TNT protein due to open reading frame disruption or to post-translational degradation of TNT.

Sporadic late-onset nemaline myopathy with monoclonal gammopathy of undetermined significance: Report of four patients.

Sporadic late-onset nemaline myopathy (SLONM) is a rare, acquired muscle disease presenting with subacute progression in adulthood. It can be accompanied by a monoclonal gammopathy of undetermined significance (MGUS). We describe clinical and histopathological findings of four SLONM patients with MGUS. In all patients, nemaline rod, inter-myofibrillary network disruption, atrophic changes, peripheral basophilic discoloration, vacuole without rim, and cytoplasmic body without inflammation were seen. Three out of four patients were treated with prednisolone in combination with IVIG monthly and had an appropriate response to the treatment. The optimal first-line treatment remains unclear in SLONM-MGUS, although corticosteroids plus IVIg is associated with favorable clinical response. These treatment modalities might be used as an optional treatment before autologous stem cell transplantation; however, further studies with a higher number of patients are required.

[A case of sporadic late-onset nemaline myopathy associated with myasthenia gravis positive for anti-titin antibody and anti-Kv1.4 antibody].

A 66-year-old woman who had myasthenia gravis (MG) admitted for type II respiratory failure and right heart failure. Although she had neither ptosis, eye movement disorder, nor diplopia, she had orbital muscles weakness, reduction of gag reflex, dysarthria, dysphagia, and mild proximal muscle weakness. Blood tests showed anti-striated muscle antibodies (anti-titin antibody and anti-Kv1.4 antibody). A muscle biopsy of the left biceps showed a marked variation in fiber size, mild mononuclear cell infiltration was seen surrounding blood vessels in perimysium and nemaline bodies in some fibers. Immunohistochemical stains showed many muscle fibers express HLA-ABC. The patient was diagnosed as sporadic late-onset nemaline myopathy (SLONM) with MG, and treated by tacrolimus. After treatment, her respiratory function gradually improved and she discharged. In the case of atypical MG, measurement of anti-striated muscle antibody or muscle biopsy should be considered.