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Yi H, Liu CX, Ye SX, Liu YL. Special electromyographic features in a child with paramyotonia congenita: A case report and review of literature. World J Clin Cases 2024; 12:587-595. [PMID: 38322461 PMCID: PMC10841953 DOI: 10.12998/wjcc.v12.i3.587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 12/04/2023] [Accepted: 01/04/2024] [Indexed: 01/18/2024] Open
Abstract
BACKGROUND Paramyotonia congenita (PMC) stands as a rare sodium channelopaty of skeletal muscle, initially identified by Eulenburg. The identification of PMC often relies on electromyography (EMG), a diagnostic technique. The child's needle EMG unveiled trains of myotonic discharges with notably giant amplitudes, alongside irregular wave trains of myotonic discharges. This distinctive observation had not surfaced in earlier studies. CASE SUMMARY We report the case of a 3-year-old female child with PMC, who exhibited laryngeal stridor, muffled speech, myotonia from birth. Cold, exposure to cool water, crying, and physical activity exacerbated the myotonia, which was relieved in warmth, yet never normalized. Percussion myotonia was observable in bilateral biceps. Myotonia symptoms remained unchanged after potassium-rich food consumption like bananas. Hyperkalemic periodic paralysis was excluded. Cranial magnetic resonance imaging yielded normal results. Blood potassium remained within normal range, while creatine kinase showed slight elevation. Exome-wide genetic testing pinpointed a heterozygous mutation on chromosome SCN4A: c.3917G>A (p.G1306E). After a six-month mexiletine regimen, symptoms alleviated. CONCLUSION In this case revealed the two types of myotonic discharges, and had not been documented in other studies. We underscore two distinctive features: Giant-amplitude potentials and irregular waves.
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Affiliation(s)
- Hui Yi
- Department of Neuroelectrophysiology, Qilu Children’s Hospital of Shandong University, Jinan 250000, Shandong Province, China
| | - Chen-Xiang Liu
- Department of Neuroelectrophysiology, University of Health and Rehabilitation Sciences (Qingdao Municipal Hospital), Qingdao 266000, Shandong Province, China
| | - Shu-Xin Ye
- Department of Neuroelectrophysiology, Qilu Children’s Hospital of Shandong University, Jinan 250000, Shandong Province, China
| | - Yu-Lin Liu
- Department of Neuroelectrophysiology, Qilu Children’s Hospital of Shandong University, Jinan 250000, Shandong Province, China
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2
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Trivedi JR. Muscle Channelopathies. Continuum (Minneap Minn) 2022; 28:1778-1799. [PMID: 36537980 DOI: 10.1212/con.0000000000001183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
PURPOSE OF REVIEW This article describes the clinical features, diagnosis, pathophysiology, and management of nondystrophic myotonia and periodic paralysis. RECENT FINDINGS An increasing awareness exists about the genotype-phenotype overlap in skeletal muscle channelopathies, and thus genetic testing is needed to make a definitive diagnosis. Electrodiagnostic testing in channelopathies is highly specialized with significant overlap in various mutation subtypes. Randomized clinical trials have now been conducted in these disorders with expanded treatment options for patients with muscle channelopathies. SUMMARY Skeletal muscle channelopathies are rare heterogeneous conditions characterized by lifelong symptoms that require a comprehensive management plan that includes pharmacologic and nonpharmacologic interventions. The significant variability in biophysical features of various mutations, coupled with the difficulties of performing clinical trials in rare diseases, makes it challenging to design and implement treatment trials for muscle channelopathies.
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Ozceylan G, Toprak D. Familial Hypokalemic Periodic Paralysis: Case Report. EURASIAN JOURNAL OF FAMILY MEDICINE 2019. [DOI: 10.33880/ejfm.2019080205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Hypokalemic periodic paralysis is a congenital disorder which is characterized by intermittent episodes of muscle weakness or paralysis. The attacks can occur everyday or once a year, may last for a few hours or for several days. Serum potassium level is low during the attack. But serum potassium levels are normal between two attacks. There is no potassium deficiency in the whole body. In this report, a 16 years old boy, whose grandfather, father and uncle had the same semptoms, and had his first attack of familial hypokalemic periodic paralysis following a grand exercise were presented according to the clinical and laboratory features.
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Affiliation(s)
| | - Dilek Toprak
- Tekirdağ Namık Kemal University School of Medicine
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Abstract
Skeletal muscle channelopathies are rare heterogeneous diseases with marked genotypic and phenotypic variability. These disorders cause lifetime disability and impact quality of life. Despite advances in understanding of the molecular pathology of these disorders, the diverse phenotypic manifestations remain a challenge in diagnosis, therapeutic, genetic counseling, and research planning. Electrodiagnostic testing is useful in directing the diagnosis, but has several limitations: patient discomfort, time consuming, and significant overlap of findings in muscle channelopathies. Although genetic testing is the gold standard in making a definitive diagnosis, a mutation might not be identified in many patients with a well-supported clinical diagnosis of periodic paralysis. In the recent past, there have been landmark clinical trials in non-dystrophic myotonia and periodic paralysis which are encouraging as they demonstrate the ability of robust clinical research consortia to conduct well-controlled trials of rare diseases.
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Affiliation(s)
- Lauren Phillips
- Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas, 75390, USA
| | - Jaya R Trivedi
- Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas, 75390, USA.
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Portaro S, Russo M, Naro A, Bramanti A, Bramanti P, Rodolico C, Calabrò RS. Advances in assessing myotonia: Can sensor-engineered glove have a role? J Neurol Sci 2017; 375:3-7. [DOI: 10.1016/j.jns.2017.01.038] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 12/17/2016] [Accepted: 01/10/2017] [Indexed: 11/24/2022]
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Fan C, Mao N, Lehmann-Horn F, Bürmann J, Jurkat-Rott K. Effects of S906T polymorphism on the severity of a novel borderline mutation I692M in Na v 1.4 cause periodic paralysis. Clin Genet 2016; 91:859-867. [PMID: 27714768 DOI: 10.1111/cge.12880] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 09/29/2016] [Accepted: 09/30/2016] [Indexed: 11/29/2022]
Abstract
Hyperkalemic periodic paralysis (HyperPP) is a dominantly inherited muscle disease caused by mutations in SCN4A gene encoding skeletal muscle voltage gated Nav 1.4 channels. We identified a novel Nav 1.4 mutation I692M in 14 families out of the 104 genetically identified HyperPP families in the Neuromuscular Centre Ulm and is therefore as frequent as I693T (13 families out of 14 HyperPP families) in Germany. Surprisingly, in 13 families, a known polymorphism S906T was also present. It was on the affected allele in at least 10 families compatible with a possible founder effect in central Europe. All affected members suffered from episodic weakness; myotonia was also common. Compared with I692M patients, I692M-S906T patients had longer weakness episodes, more affected muscles, CK elevation and presence of permanent weakness. Electrophysiological investigation showed that both mutants had incomplete slow inactivation and a hyperpolarizing shift of activation which contribute to membrane depolarization and weakness. Additionally, I692M-S906T significantly enhanced close-state fast inactivation compared with I692M alone, suggesting a higher proportion of inactivated I692M-S906T channels upon membrane depolarization which may facilitate the initiation of weakness episodes and therefore clinical manifestation. Our results suggest that polymorphism S906T has effects on the clinical phenotypic and electrophysiological severity of a novel borderline Nav 1.4 mutation I692M, making the borderline mutation fully penetrant.
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Affiliation(s)
- C Fan
- Division of Neurophysiology, Ulm University, Ulm, Germany
| | - N Mao
- Division of Neurophysiology, Ulm University, Ulm, Germany.,Human Oncology & Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - F Lehmann-Horn
- Division of Neurophysiology, Ulm University, Ulm, Germany
| | - J Bürmann
- Department of Neurology, University Hospital of the Saarland, Homburg, Germany
| | - K Jurkat-Rott
- Dept. of Neurosurgery, Ulm University, Albert-Einstein-Allee 23,89081 Ulm, Germany
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7
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Abstract
OPINION STATEMENT Neuromuscular channelopathies are heterogeneous disorders with marked phenotypic and genotypic variability. These include non-dystrophic myotonia (NDM), periodic paralysis (PP), and congenital myasthenic syndrome (CMS). Their diverse clinical manifestations remain a challenge in diagnosis and management to this date. These disorders impact quality of life and cause lifelong disabling symptoms. Treatment options are few and not FDA-approved. This is largely due to a paucity of large, randomized clinical trials in these rare diseases. Challenges of conducting such trials include the rarity of these disorders and the genetic heterogeneity. Physicians rely on off-label use of drugs to treat muscle channelopathies to reduce morbidity and improve quality of life. Besides pharmacological treatment, dietary modifications, lifestyle changes, awareness of triggers, and genetic counseling also play an important role in long-term disease management. This article reviews the current management strategies for neuromuscular channelopathies.
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9
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Trivedi JR, Cannon SC, Griggs RC. Nondystrophic myotonia: challenges and future directions. Exp Neurol 2013; 253:28-30. [PMID: 24361411 DOI: 10.1016/j.expneurol.2013.12.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2013] [Revised: 11/27/2013] [Accepted: 12/10/2013] [Indexed: 12/29/2022]
Abstract
Non-dystrophic myotonias are rare diseases caused by mutations in skeletal muscle chloride and sodium ion channels with considerable phenotypic overlap between diseases. Common symptoms include muscle stiffness, transitory weakness, fatigue, and pain. Although seldom life-shortening, these myotonias cause life-time disability and affected individuals cannot perform many daily activities. A notable feature of the recessive form of chloride channelopathies is the presence of transient weakness. While there has been considerable progress in skeletal muscle channelopathies with regards to identifying biophysical abnormalities, the mechanism of transient weakness remains unclear. A recent study published in Experimental Neurology (Desaphy et al., 2013) explored this question further by comparing the biophysical properties of 3 chloride channel mutations associated with recessive myotonia congenita, with varying susceptibility to transient weakness. The authors identified a variety of functional defects in channel behavior among the 3 mutations, suggesting that this variability contributes to the differing phenotypes among chloride channelopathies. This commentary discusses nondystrophic myotonias, the results of Desaphy et al., and the treatment challenges in this rare disease.
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Affiliation(s)
- Jaya R Trivedi
- Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, Dallas, TX 75390, USA.
| | - Stephen C Cannon
- Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Robert C Griggs
- Department of Neurology, University of Rochester Medical Center, Rochester, NY, USA
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Trivedi JR, Bundy B, Statland J, Salajegheh M, Rayan DR, Venance SL, Wang Y, Fialho D, Matthews E, Cleland J, Gorham N, Herbelin L, Cannon S, Amato A, Griggs RC, Hanna MG, Barohn RJ. Non-dystrophic myotonia: prospective study of objective and patient reported outcomes. ACTA ACUST UNITED AC 2013; 136:2189-200. [PMID: 23771340 DOI: 10.1093/brain/awt133] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Non-dystrophic myotonias are rare diseases caused by mutations in skeletal muscle chloride and sodium ion channels with considerable phenotypic overlap between diseases. Few prospective studies have evaluated the sensitivity of symptoms and signs of myotonia in a large cohort of patients. We performed a prospective observational study of 95 participants with definite or clinically suspected non-dystrophic myotonia recruited from six sites in the USA, UK and Canada between March 2006 and March 2009. We used the common infrastructure and data elements provided by the NIH-funded Rare Disease Clinical Research Network. Outcomes included a standardized symptom interview and physical exam; the Short Form-36 and the Individualized Neuromuscular Quality of Life instruments; electrophysiological short and prolonged exercise tests; manual muscle testing; and a modified get-up-and-go test. Thirty-two participants had chloride channel mutations, 34 had sodium channel mutations, nine had myotonic dystrophy type 2, one had myotonic dystrophy type 1, and 17 had no identified mutation. Phenotype comparisons were restricted to those with sodium channel mutations, chloride channel mutations, and myotonic dystrophy type 2. Muscle stiffness was the most prominent symptom overall, seen in 66.7% to 100% of participants. In comparison with chloride channel mutations, participants with sodium mutations had an earlier age of onset of stiffness (5 years versus 10 years), frequent eye closure myotonia (73.5% versus 25%), more impairment on the Individualized Neuromuscular Quality of Life summary score (20.0 versus 9.44), and paradoxical eye closure myotonia (50% versus 0%). Handgrip myotonia was seen in three-quarters of participants, with warm up of myotonia in 75% chloride channel mutations, but also 35.3% of sodium channel mutations. The short exercise test showed ≥10% decrement in the compound muscle action potential amplitude in 59.3% of chloride channel participants compared with 27.6% of sodium channel participants, which increased post-cooling to 57.6% in sodium channel mutations. In evaluation of patients with clinical and electrical myotonia, despite considerable phenotypic overlap, the presence of eye closure myotonia, paradoxical myotonia, and an increase in short exercise test sensitivity post-cooling suggest sodium channel mutations. Outcomes designed to measure stiffness or the electrophysiological correlates of stiffness may prove useful for future clinical trials, regardless of underlying mutation, and include patient-reported stiffness, bedside manoeuvres to evaluate myotonia, muscle specific quality of life instruments and short exercise testing.
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Affiliation(s)
- Jaya R Trivedi
- Department of Neurology and Neurotherapeutics, UT Southwestern Medical Centre, Dallas, TX 75390, USA.
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Zhao J, Duprè N, Puymirat J, Chahine M. Biophysical characterization of M1476I, a sodium channel founder mutation associated with cold-induced myotonia in French Canadians. J Physiol 2012; 590:2629-44. [PMID: 22250216 DOI: 10.1113/jphysiol.2011.223461] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
M1476I, a French Canadian founder mutation of Na⁺ channel Nav1.4, causes potassium-aggravated myotonia, with cold-induced myotonia as the most distinctive clinical feature. Mexiletine, a class 1B local anaesthetic, relieves the myotonic symptoms of patients carrying the M1476I mutation. We used the patch-clamp method to investigate the functional characteristics of this mutation by heterologous expression in tsA201 cells. The M1476I mutation caused an increased persistent Na⁺ current, a 2- to 3-fold slower fast inactivation, a 6.4 mV depolarizing shift in the midpoint of steady-state inactivation, and an accelerated recovery from fast inactivation compared to the wild-type (WT) channel. Cooling slowed the kinetics of both channel types and increased the amplitude of the persistent current in M1476I channels.Mexiletine suppressed the persistent Na⁺ current generated by the M1476I mutation and blocked both WT and M1476I channels in a use- dependent manner. The inactivation-deficient M1476I channels were less susceptible to mexiletine during repetitive pulses. The decreased use-dependent block of M1476I channels might have resulted from the slower onset of mexiletine block, and/or the faster recovery from mexiletine block, given that the affinity of mexiletine for the inactivated state of the WT and mutant channels was similar. Increased extracellular concentrations of potassium had no effect on either M1476I or WT currents. These results indicated that cooling can augment the disruption of the voltage dependence of fast inactivation by M1476I channels.
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Affiliation(s)
- Juan Zhao
- Le Centre de recherche en neurosciences, Institut universitaire en santé mentale de Québec, 2601 Chemin de Canardière, Quebec, QC, G1J 2G3, Canada
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12
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Mobasheri A, Barrett-Jolley R. Transient receptor potential channels: emerging roles in health and disease. Vet J 2010; 187:145-6. [PMID: 20304688 DOI: 10.1016/j.tvjl.2010.02.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Accepted: 02/05/2010] [Indexed: 12/23/2022]
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13
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Fishman O, Sogawa Y, Moshé SL. Transient axial hypotonia and alteration of consciousness in an infant with Chiari I malformation. Semin Pediatr Neurol 2010; 17:17-23. [PMID: 20434687 DOI: 10.1016/j.spen.2010.01.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- Olga Fishman
- Saul R. Korey Department of Neurology, Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, NY 10467, USA.
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Chrestian N, Puymirat J, Bouchard JP, Dupré N. Myotonia congenita--a cause of muscle weakness and stiffness. ACTA ACUST UNITED AC 2006; 2:393-9; quiz following 399. [PMID: 16932590 DOI: 10.1038/ncpneuro0239] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Accepted: 04/25/2006] [Indexed: 11/08/2022]
Abstract
BACKGROUND A 56-year-old woman was referred to a neurogenetic clinic with a history of stiffness and transient weakness. A previous needle electromyogram had confirmed the presence of myotonia, but a muscle biopsy had revealed no evidence of dystrophy. INVESTIGATIONS Neurological examination, electrophysiological studies and genetic testing. DIAGNOSIS Recessive myotonia congenita (Becker's disease). MANAGEMENT Explanation of the nature of the disease and treatment with mexiletine 200 mg twice daily.
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Torbergsen T, Hødnebø A, Brautaset NJ, Løseth S, Stålberg E. A rare form of painful nondystrophic myotonia. Clin Neurophysiol 2003; 114:2347-54. [PMID: 14652094 DOI: 10.1016/s1388-2457(03)00275-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
OBJECTIVE In this paper we report a painful nondystrophic myotonia which has not been previously described. Pain is a rare symptom in myotonia. We report a myotonic disorder in a 34-year-old woman and her 14-year-old daughter. Painful cramps occur during and after exercise in the mother, and both patients can demonstrate unusual contractions in the tongue. In the present study we try to evaluate the mechanisms behind the unique finding of trains of high amplitude of positive waves, not seen in the earlier known myotonic conditions. METHODS Clinical investigations and electromyography with single and dual channel recordings and muscle morphometry were performed. RESULTS The electromyographic recordings reveal positive waves, fibrillation potentials and myotonic discharges. In addition, extraordinary findings were made of trains of high frequency positive potentials with very high amplitudes and with conduction block along the muscle fibres. CONCLUSIONS In this new form of myotonia with likely dominant heredity, the specific finding of trains of high amplitude positive waves indicates ephaptic transmission within bundles of neighbouring muscle fibres.
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Affiliation(s)
- T Torbergsen
- Department of Neurology, Tromsø University Hospital, Tromsø, Norway.
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Mutlu GM, Factor P. Acute-onset quadriplegia, respiratory failure, and ventricular tachycardia in a 21-year-old man following a soccer match. Chest 2002; 121:2036-9. [PMID: 12065374 DOI: 10.1378/chest.121.6.2036] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Affiliation(s)
- Gökhan M Mutlu
- Division of Pulmonary and Critical Care Medicine, Evanston Northwestern Healthcare, Evanston, Northwestern University Medical School, Chicago, IL 60201, USA.
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17
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Peng S, Rapoport SI, Pearce RJ, Galdzicki Z. Abnormal chloride and potassium conductances in cultured embryonic tongue muscle from trisomy 16 mouse. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2000; 122:193-7. [PMID: 10960688 DOI: 10.1016/s0165-3806(00)00058-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Trisomy 16 (Ts16) mouse is considered an animal model of Down syndrome (human trisomy 21). Whole-cell patch-clamp was used to evaluate potassium and chloride currents of cultured tongue muscle cells from fetal Ts16 and diploid mice. No difference was found in membrane capacitance between the two groups. K(+) and Cl(-) currents were pharmacologically isolated. K(+) conductance was reduced by 31% in Ts16 cells (373 pS/pF) compared with diploid cells (539 pS/pF). Cl(-) conductance was 51% larger in Ts16 cells (103 pS/pF) compared with diploid cells (68 pS/pF). However kinetics for K(+) and Cl(-) currents did not differ between the cell types. An increase in Cl(-) conductance and a decrease in K(+) conductance in Ts16 muscle cells, if present in muscle of Down syndrome subjects, might account for the observed hypotonia in these subjects.
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Affiliation(s)
- S Peng
- Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Room 6C-103, Building 10, 9000 Rockville Pike, Bethesda, Maryland, MD 20892, USA
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Abstract
The periodic paralyses are a group of muscle diseases with abnormalities of channels. These abnormalities result in paralysis or weakness with or without poor relaxation of muscle. Hypokalemic periodic paralyses, potassium-sensitive periodic paralyses, and paramyotonia congenita are reviewed. The clinical findings, pathophysiologic abnormalities, diagnostic evaluations, and possible treatments are included in this article.
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Affiliation(s)
- L Gutmann
- Department of Neurology, West Virginia University School of Medicine, Morgantown, WV 26506, USA
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19
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Abstract
KATP channels are a newly defined class of potassium channels based on the physical association of an ABC protein, the sulfonylurea receptor, and a K+ inward rectifier subunit. The beta-cell KATP channel is composed of SUR1, the high-affinity sulfonylurea receptor with multiple TMDs and two NBFs, and KIR6.2, a weak inward rectifier, in a 1:1 stoichiometry. The pore of the channel is formed by KIR6.2 in a tetrameric arrangement; the overall stoichiometry of active channels is (SUR1/KIR6.2)4. The two subunits form a tightly integrated whole. KIR6.2 can be expressed in the plasma membrane either by deletion of an ER retention signal at its C-terminal end or by high-level expression to overwhelm the retention mechanism. The single-channel conductance of the homomeric KIR6.2 channels is equivalent to SUR/KIR6.2 channels, but they differ in all other respects, including bursting behavior, pharmacological properties, sensitivity to ATP and ADP, and trafficking to the plasma membrane. Coexpression with SUR restores the normal channel properties. The key role KATP channel play in the regulation of insulin secretion in response to changes in glucose metabolism is underscored by the finding that a recessive form of persistent hyperinsulinemic hypoglycemia of infancy (PHHI) is caused by mutations in KATP channel subunits that result in the loss of channel activity. KATP channels set the resting membrane potential of beta-cells, and their loss results in a constitutive depolarization that allows voltage-gated Ca2+ channels to open spontaneously, increasing the cytosolic Ca2+ levels enough to trigger continuous release of insulin. The loss of KATP channels, in effect, uncouples the electrical activity of beta-cells from their metabolic activity. PHHI mutations have been informative on the function of SUR1 and regulation of KATP channels by adenine nucleotides. The results indicate that SUR1 is important in sensing nucleotide changes, as implied by its sequence similarity to other ABC proteins, in addition to being the drug sensor. An unexpected finding is that the inhibitory action of ATP appears to be through a site located on KIR6.2, whose affinity for ATP is modified by SUR1. A PHHI mutation, G1479R, in the second NBF of SUR1 forms active KATP channels that respond normally to ATP, but fail to activate with MgADP. The result implies that ATP tonically inhibits KATP channels, but that the ADP level in a fasting beta-cell antagonizes this inhibition. Decreases in the ADP level as glucose is metabolized result in KATP channel closure. Although KATP channels are the target for sulfonylureas used in the treatment of NIDDM, the available data suggest that the identified KATP channel mutations do not play a major role in diabetes. Understanding how KATP channels fit into the overall scheme of glucose homeostasis, on the other hand, promises insight into diabetes and other disorders of glucose metabolism, while understanding the structure and regulation of these channels offers potential for development of novel compounds to regulate cellular electrical activity.
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Affiliation(s)
- L Aguilar-Bryan
- Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA
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Moxley RT. 54th ENMC International Workshop: PROMM (proximal myotonic myopathies) and other proximal myotonic syndromes. 10-12th October 1997, Naarden, The Netherlands. Neuromuscul Disord 1998; 8:508-18. [PMID: 9829282 DOI: 10.1016/s0960-8966(98)00068-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Abstract
Ion channels are essential to a wide range of physiological functions including neuronal signaling, muscle contraction, cardiac pacemaking, hormone secretion and cell proliferation. The important role that highly regulated ion influx plays in these processes has been underscored by a recent flurry of discoveries linking ion-channel gene mutations to inherited disorders. Ion channels of many different types have been demonstrated as being causative factors in genetic disease. This review discusses the growing number of disorders associated with genes of the voltage-gated ion channel superfamily, with special focus on those characterized by neurological, neuromuscular, or cardiac dysfunction in humans and mice.
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Affiliation(s)
- J L Doyle
- Division, Oak Ridge National Laboratory, TN 37831-8077, USA
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