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Muscle Disorders
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Kourosh Rezania, Peter Pytel, Betty Soliven
Paramyotonia congenita is an autosomal dominant disorder characterized by episodic cold-induced or exercise-induced myotonia in exposed areas lasting minutes to hours. Potassium-aggravated myotonias (PAMs) are characterized by worsening of myotonia with potassium ingestion and include myotonia fluctuans, myotonia permanens, and acetazolamide-sensitive myotonia.
Neurogenetics
Published in John W. Scadding, Nicholas A. Losseff, Clinical Neurology, 2011
Sonia Gandhi, Sarah Tabrizi, Nicholas Wood
Myotonia is a disorder in which muscle stiffness occurs as a result of failure of muscle relaxation. Myotonia congenita may be dominant (Thomsen’s disease) or recessive (Becker’s disease). Myotonia may be detected clinically or on electromyography (EMG). Both types are caused by mutations in the muscle chloride channel gene (CLCN1). Paramyotonia congenita is a myotonic autosomal dominant disorder that occurs during exercise and, in contrast to myotonia congenita, worsens with activity. This disorder is caused by mutations in the muscle sodium channel SCN4A, which also causes hyperkalaemic periodic paralysis.
Sodium Channel Myotonia and a Novel Gly701Asp Mutation in the SCN4A Gene: From an Ophthalmological Symptom to a Familial Disease
Published in Neuro-Ophthalmology, 2021
Filipa Sampaio, Sérgia Soares, Sara Pereira, José Alberto Lemos, Ágata Mota
The non-dystrophic myotonias are caused by dysfunction of key skeletal muscle ion channels. The worldwide prevalence of non-dystrophic myotonia has been estimated to be 1 in 100 000.1 The major clinical manifestation of the non-dystrophic myotonias is muscle stiffness and additional common symptoms include pain, weakness and fatigue.2,3 Myotonia can be demonstrated on examination as delayed muscle relaxation following muscle contraction. Non-dystrophic myotonias are classified as myotonia congenita, caused by mutations in the skeletal muscle chloride channel gene (CLCN1) and inherited in a dominant or in a recessive fashion; paramyotonia congenita and the sodium channel myotonias, characterised by allelic, autosomal dominant disorders caused by mutations in the skeletal muscle sodium channel gene (SCN4A); and hyperkalaemic periodic paralysis, also caused by mutations in SCN4A gene in which episodic paralysis is usually the dominant feature (Table 1).4
Improving genetic diagnostics of skeletal muscle channelopathies
Published in Expert Review of Molecular Diagnostics, 2020
Vinojini Vivekanandam, Roope Männikkö, Emma Matthews, Michael G. Hanna
Paramyotonia congenita (PMC) and Sodium channel myotonia (SCM) are caused by mutations in the SCN4A gene encoding the alpha sub-unit of the voltage-gated sodium channel, Nav1.4. The mutant channels show a gain of channel function on heterologous expression [8]. Both conditions are inherited in a dominant fashion. Patients with paramyotonia congenita can be particularly sensitive to cold and have ‘paradoxical warm-up’ phenomenon where myotonia worsens with repeated contraction [9]. They may also have episodic muscle weakness or paralysis. This episodic weakness is not seen in Sodium Channel Myotonia [10].
Ophthalmological Manifestations of Hereditary Myopathies
Published in Journal of Binocular Vision and Ocular Motility, 2022
Marta Saint-Gerons, Miguel Angel Rubio, Gemma Aznar, Ana Matheu
Paramyotonia congenita (PM) is a non-dystrophic myopathy caused by mutations in the SCN4A gene. Mutations in SCN4A are associated with different ionic channelopathies.57 PM can be confused with myotonia congenita.59 Beginning in infancy or early childhood, myotonia causes muscle stiffness that typically occurs after exercise and can be induced by muscle cooling.60 Ocular manifestations include eyelid myotonia (with lid-lag sign) and saccade alterations.31,61