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ELife Apr 2021In addition to the hallmark muscle stiffness, patients with recessive myotonia congenita (Becker disease) experience debilitating bouts of transient weakness that remain...
In addition to the hallmark muscle stiffness, patients with recessive myotonia congenita (Becker disease) experience debilitating bouts of transient weakness that remain poorly understood despite years of study. We performed intracellular recordings from muscle of both genetic and pharmacologic mouse models of Becker disease to identify the mechanism underlying transient weakness. Our recordings reveal transient depolarizations (plateau potentials) of the membrane potential to -25 to -35 mV in the genetic and pharmacologic models of Becker disease. Both Na and Ca currents contribute to plateau potentials. Na persistent inward current (NaPIC) through Na1.4 channels is the key trigger of plateau potentials and current through Ca1.1 Ca channels contributes to the duration of the plateau. Inhibiting NaPIC with ranolazine prevents the development of plateau potentials and eliminates transient weakness in vivo. These data suggest that targeting NaPIC may be an effective treatment to prevent transient weakness in myotonia congenita.
Topics: Animals; Disease Models, Animal; Female; Male; Membrane Potentials; Mice; Myotonia Congenita; Sodium
PubMed: 33904400
DOI: 10.7554/eLife.65691 -
Pathogenic variants in TNNC2 cause congenital myopathy due to an impaired force response to calcium.The Journal of Clinical Investigation May 2021Troponin C (TnC) is a critical regulator of skeletal muscle contraction; it binds Ca2+ to activate muscle contraction. Surprisingly, the gene encoding fast skeletal TnC...
Troponin C (TnC) is a critical regulator of skeletal muscle contraction; it binds Ca2+ to activate muscle contraction. Surprisingly, the gene encoding fast skeletal TnC (TNNC2) has not yet been implicated in muscle disease. Here, we report 2 families with pathogenic variants in TNNC2. Patients present with a distinct, dominantly inherited congenital muscle disease. Molecular dynamics simulations suggested that the pathomechanisms by which the variants cause muscle disease include disruption of the binding sites for Ca2+ and for troponin I. In line with these findings, physiological studies in myofibers isolated from patients' biopsies revealed a markedly reduced force response of the sarcomeres to [Ca2+]. This pathomechanism was further confirmed in experiments in which contractile dysfunction was evoked by replacing TnC in myofibers from healthy control subjects with recombinant, mutant TnC. Conversely, the contractile dysfunction of myofibers from patients was repaired by replacing endogenous, mutant TnC with recombinant, wild-type TnC. Finally, we tested the therapeutic potential of the fast skeletal muscle troponin activator tirasemtiv in patients' myofibers and showed that the contractile dysfunction was repaired. Thus, our data reveal that pathogenic variants in TNNC2 cause congenital muscle disease, and they provide therapeutic angles to repair muscle contractility.
Topics: Binding Sites; Calcium; Humans; Molecular Dynamics Simulation; Muscle Contraction; Myotonia Congenita; Sarcomeres; Troponin C
PubMed: 33755597
DOI: 10.1172/JCI145700 -
Acta Neurologica Belgica Jun 2022Nemaline myopathy (NM) is a congenital myopathy of great heterogeneity, characterized by the presence of rods in the cytoplasm of muscle fibers. The samples of 16...
Nemaline myopathy (NM) is a congenital myopathy of great heterogeneity, characterized by the presence of rods in the cytoplasm of muscle fibers. The samples of 16 nemaline myopathy patients diagnosed by characteristically pathological features went through whole exon sequencing. Clinico-pathological and genetic features of the cases were systematically analyzed. According to the classification of nemaline myopathy by ENMC, 8 cases are typical congenital subtype, 6 cases are childhood/juvenile onset subtype and 2 case are adult onset subtype. In histological findings, characteristic purple-colored rods are discovered under modified gömöri trichrome staining (MGT). Electron microscopy revealed the presence of high electron-dense nemaline bodies around the submucosa and the nucleus nine patients (9/16 56.3%) were detected pathogenic causative mutations, among whom mutations in the NEB gene were the most frequent (6 patients, 66.7%). KBTBD13 gene mutation was discovered in two patients and ACTA1 gene mutation was discovered in 1 patient. Nemaline myopathy is a congenital myopathy with highly clinico-pathological and genetic heterogeneity. NEB gene mutation is the most common mutation, in which splicing change c.21522 +3A > G is hotspot mutation in Chinese NM patients.
Topics: Adult; Asian People; Child; China; Humans; Muscle Proteins; Muscle, Skeletal; Muscular Diseases; Mutation; Myopathies, Nemaline; Myotonia Congenita
PubMed: 33742414
DOI: 10.1007/s13760-020-01542-9 -
Cells Feb 2021Non-dystrophic myotonias have been linked to loss-of-function mutations in the ClC-1 chloride channel or gain-of-function mutations in the Na1.4 sodium channel. Here, we...
Non-dystrophic myotonias have been linked to loss-of-function mutations in the ClC-1 chloride channel or gain-of-function mutations in the Na1.4 sodium channel. Here, we describe a family with members diagnosed with Thomsen's disease. One novel mutation (p.W322*) in and one undescribed mutation (p.R1463H) in are segregating in this family. The -p.W322* was also found in an unrelated family, in compound heterozygosity with the known -p.G355R mutation. One reported mutation, -p.T1313M, was found in a third family. Both mutations exhibited loss-of-function: -p.W322* probably leads to a non-viable truncated protein; for -p.G355R, we predict structural damage, triggering important steric clashes. The -p.R1463H produced a positive shift in the steady-state inactivation increasing window currents and a faster recovery from inactivation. These gain-of-function effects are probably due to a disruption of interaction R1463-D1356, which destabilizes the voltage sensor domain (VSD) IV and increases the flexibility of the S4-S5 linker. Finally, modelling suggested that the p.T1313M induces a strong decrease in protein flexibility on the III-IV linker. This study demonstrates that -p.W322* and -p.R1463H mutations can act alone or in combination as inducers of myotonia. Their co-segregation highlights the necessity for carrying out deep genetic analysis to provide accurate genetic counseling and management of patients.
Topics: Chloride Channels; Female; Genetic Testing; Humans; Male; Middle Aged; Mutation; Myotonia; Myotonia Congenita; NAV1.4 Voltage-Gated Sodium Channel; Pedigree
PubMed: 33670307
DOI: 10.3390/cells10020374 -
Molecular Genetics & Genomic Medicine Feb 2021Myotonia congenita (MC) is a common channelopathy affecting skeletal muscle and which is due to pathogenic variants within the CLCN1 gene. Various alterations in the...
Functional analysis of the F337C mutation in the CLCN1 gene associated with dominant myotonia congenita reveals an alteration of the macroscopic conductance and voltage dependence.
BACKGROUND
Myotonia congenita (MC) is a common channelopathy affecting skeletal muscle and which is due to pathogenic variants within the CLCN1 gene. Various alterations in the function of the channel have been reported and we here illustrate a novel one.
METHODS
A patient presenting the symptoms of myotonia congenita was shown to bear a new heterozygous missense variant in exon 9 of the CLCN1 gene (c.1010 T > G, p.(Phe337Cys)). Confocal imaging and patch clamp recordings of transiently transfected HEK293 cells were used to functionally analyze the effect of this variant on channel properties.
RESULTS
Confocal imaging showed that the F337C mutant incorporated as well as the WT channel into the plasma membrane. However, in patch clamp, we observed a smaller conductance for F337C at -80 mV. We also found a marked reduction of the fast gating component in the mutant channels, as well as an overall reduced voltage dependence.
CONCLUSION
To our knowledge, this is the first report of a mixed alteration in the biophysical properties of hClC-1 consisting of a reduced conductance at resting potential and an almost abolished voltage dependence.
Topics: Action Potentials; Cell Membrane; Chloride Channels; HEK293 Cells; Humans; Ion Channel Gating; Mutation, Missense; Myotonia Congenita; Protein Transport
PubMed: 33507632
DOI: 10.1002/mgg3.1588 -
Acta Neuropathologica Mar 2021Mutations 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...
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.
Topics: Adolescent; Adult; Aged; Child; Child, Preschool; Connectin; Female; Humans; Infant; Male; Middle Aged; Mutation, Missense; Myotonia Congenita; Young Adult
PubMed: 33449170
DOI: 10.1007/s00401-020-02257-0 -
Journal of Biomedical Science Jan 2021Congenital myopathy (CM) is a group of clinically and genetically heterogeneous muscle disorders, characterized by muscle weakness and hypotonia from birth. Currently,...
BACKGROUND
Congenital myopathy (CM) is a group of clinically and genetically heterogeneous muscle disorders, characterized by muscle weakness and hypotonia from birth. Currently, no definite treatment exists for CM. A de novo mutation in Tropomyosin 3-TPM3(E151G) was identified from a boy diagnosed with CM, previously TPM3(E151A) was reported to cause CM. However, the role of TPM3(E151G) in CM is unknown.
METHODS
Histopathological, swimming behavior, and muscle endurance were monitored in TPM3 wild-type and mutant transgenic fish, modelling CM. Gene expression profiling of muscle of the transgenic fish were studied through RNAseq, and mitochondria respiration was investigated.
RESULTS
While TPM3(WT) and TPM3(E151A) fish show normal appearance, amazingly a few TPM3(E151G) fish display either no tail, a crooked body in both F0 and F1 adults. Using histochemical staining for the muscle biopsy, we found TPM3(E151G) displays congenital fiber type disproportion and TPM3(E151A) resembles nemaline myopathy. TPM3(E151G) transgenic fish dramatically swimming slower than those in TPM3(WT) and TPM3(E151A) fish measured by DanioVision and T-maze, and exhibit weaker muscle endurance by swimming tunnel instrument. Interestingly, L-carnitine treatment on TPM3(E151G) transgenic larvae significantly improves the muscle endurance by restoring the basal respiration and ATP levels in mitochondria. With RNAseq transcriptomic analysis of the expression profiling from the muscle specimens, it surprisingly discloses large downregulation of genes involved in pathways of sodium, potassium, and calcium channels, which can be rescued by L-carnitine treatment, fatty acid metabolism was differentially dysregulated in TPM3(E151G) fish and rescued by L-carnitine treatment.
CONCLUSIONS
These results demonstrate that TPM3(E151G) and TPM3(E151A) exhibit different pathogenicity, also have distinct gene regulatory profiles but the ion channels were downregulated in both mutants, and provides a potential mechanism of action of TPM3 pathophysiology. Our results shed a new light in the future development of potential treatment for TPM3-related CM.
Topics: Animals; Animals, Genetically Modified; Carnitine; Muscle, Skeletal; Myotonia Congenita; Tropomyosin; Zebrafish
PubMed: 33435938
DOI: 10.1186/s12929-020-00707-1 -
Obstetric Medicine Dec 2020Paramyotonia congenita is a rare autosomal dominant non-dystrophic myopathy caused by mutations in the SNC4A gene, which encodes for the voltage-gated sodium channel in...
Paramyotonia congenita is a rare autosomal dominant non-dystrophic myopathy caused by mutations in the SNC4A gene, which encodes for the voltage-gated sodium channel in skeletal muscle. Symptom onset is typically during early childhood and is characterised by myotonia followed by flaccid paralysis or weakness, usually exacerbated by repeated muscle contractions or cold temperatures. Pregnancy has been reported to increase symptoms of myotonia; however, there is limited information in the literature regarding the possible effects of paramyotonia congenita on pregnancy and labour. We present a successful case of a 20-year-old primigravida with confirmed paramyotonia congenita and review the literature regarding paramyotonia congenita during pregnancy.
PubMed: 33343696
DOI: 10.1177/1753495X18816171 -
Frontiers in Physiology 2020Reduced Cl conductance causes inhibited muscle relaxation after forceful voluntary contraction due to muscle membrane hyperexcitability. This represents the...
Reduced Cl conductance causes inhibited muscle relaxation after forceful voluntary contraction due to muscle membrane hyperexcitability. This represents the pathomechanism of myotonia congenita. Due to the prevailing data suggesting that an increased potassium level is a main contributor, we studied the effect of a modulator of a big conductance Ca- and voltage-activated K channels (BK) modulator on contraction and relaxation of slow- and high-twitch muscle specimen before and after the pharmacological induction of myotonia. Human and murine muscle specimens (wild-type and BK) were exposed to anthracene-9-carboxylic acid (9-AC) to inhibit CLC-1 chloride channels and to induce myotonia . Functional effects of BK-channel activation and blockade were investigated by exposing slow-twitch (soleus) and fast-twitch (extensor digitorum longus) murine muscle specimens or human musculus vastus lateralis to an activator (NS1608) and a blocker (Paxilline), respectively. Muscle-twitch force and relaxation times (T) were monitored. Compared to wild type, fast-twitch muscle specimen of BK mice resulted in a significantly decreased T in presence of 9-AC. Paxilline significantly shortened T of murine slow- and fast-twitch muscles as well as human vastus lateralis muscle. Moreover, twitch force was significantly reduced after application of Paxilline in myotonic muscle. NS1608 had opposite effects to Paxilline and aggravated the onset of myotonic activity by prolongation of T. The currently used standard therapy for myotonia is, in some individuals, not very effective. This study demonstrated that a BK channel blocker lowers myotonic stiffness and thus highlights its potential therapeutic option in myotonia congenital (MC).
PubMed: 33329012
DOI: 10.3389/fphys.2020.533946