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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
HypoPP is an autosomal dominant disorder characterized by episodes of flaccid muscle weakness associated with hypokalemia. Types of hypoPP include: HypoPP1 (mutations in calcium channel gene [CACNA1S] dihydropyridine receptor) (most common).HypoPP2 (SCN4A mutations).HypoPP3 (KCNE3).Thyrotoxic periodic paralysis (KCNJ18).Andersen–Tawil syndrome (KCNJ2): 65% hypokalemic, remainder normokalemic or hyperkalemic; characteristic facies and long QT arrhythmia present.Distal renal tubular acidosis (SLC4A1).
Histopathology of the Conduction System in Long QT Syndrome
Published in Fetal and Pediatric Pathology, 2022
Alexandra Rogers, Rachel Taylor, Janet Poulik, Bahig M. Shehata
A less common, but significant variant of LQTS is LQT7, also known as Andersen-Tawil Syndrome. The majority of ATS cases are caused by mutations in the KCNJ2 gene and follow an autosomal dominant inheritance pattern. About 50% of individuals diagnosed with ATS have a parent with the condition and the remaining 50% are thought to develop the disease via de novo mutation of the KCNJ2 gene [4]. Symptoms of Andersen-Tawil Syndrome include periodic paralysis, cardiac arrhythmias, and developmental abnormalities (with mild learning disabilities), as well as physical anomalies such as micrognathia, clinodactyly, and scoliosis [4]. ATS typically presents in the second decade of life as cardiac symptoms and/or episodes of muscle weakness which can last anywhere from several hours to several days. Sometimes these periods of flaccid paralysis occur during extended times of rest or during rest following exertion; other times they happen without any clear trigger. Episodic paralysis can be treated with oral potassium if serum levels are low, or intake of carbohydrates if serum potassium is elevated [4]. It has also been shown that mild exertion can help mitigate the length and severity of these episodes. Andersen-Tawil Syndrome is not curable, but can be managed by avoiding QTc-prolonging medications and by maintaining an appropriate diet and consistent exercise.
Improving genetic diagnostics of skeletal muscle channelopathies
Published in Expert Review of Molecular Diagnostics, 2020
Vinojini Vivekanandam, Roope Männikkö, Emma Matthews, Michael G. Hanna
While there is currently no cure, symptomatic management in these groups can be very effective. Sodium channel blockers have been used to reduce myotonia. Mexiletine has been shown to be effective in a large randomized-controlled multi-center trial [19]. Potassium supplementation, or potassium-sparing agents such as spironolactone may be effective in hypokalaemic periodic paralysis [20] and potassium wasting diuretics, e.g. thiazides in hyperkalemic periodic paralysis. Acetazolamide and other carbonic anhydrase inhibitors can be effective in reducing symptoms of muscle weakness in all forms of periodic paralysis [21]. Cardiac screening is essential in Andersen-Tawil Syndrome because of the risk of cardiac arrhythmia [15]. Education about the condition, trigger avoidance and lifestyle management is pivotal.
Precision medicine in cardiac electrophysiology: where we are and where we need to go
Published in Expert Review of Precision Medicine and Drug Development, 2020
Ashish Correa, Syed Waqas Haider, Wilbert S. Aronow
Congenital LQTS is an inherited arrhythmia syndrome characterized by a prolonged QT interval on the surface electrocardiogram (EKG) resulting from abnormal cardiac repolarization that puts an individual at an increased risk for a particular type of polymorphic ventricular tachycardia known as torsades des pointes [20,21]. LQTS are divided into 13 subtypes based on 13 genotypes that have been identified. Each genotype is due to a mutation of a discrete gene. Phenotypically, the disease may present as a cardiac arrhythmia syndrome alone or one associated with other conditions. When occurring without any other associated conditions, it is known as Romano-Ward Syndrome – an LQTS that can be caused by mutations of any the 13 identified genes and with autosomal dominant inheritance [20,22,23]. Other rarer phenotypes of LQTS include Jervell and Lange-Nielsen Syndrome, Andersen-Tawil Syndrome, and Timothy Syndrome. Jervell and Lange-Nielsen Syndrome (JLNS) is an extremely severe and rare autosomal recessive disorder characterized by marked QT prolongation with high rates of SCD as well as sensorineural deafness [24]. Andersen-Tawil Syndrome, also known as hypokalemic periodic paralysis or long QT syndrome 7 (LQT7) is an autosomal dominant disorder characterized by a triad of a prolonged QT interval with ventricular arrhythmias, potassium-sensitive periodic paralysis and various dysmorphic features [25,26]. Timothy Syndrome or LQT8 is an extremely rare autosomal recessive arrhythmia syndrome characterized by various arrhythmias, QT prolongation, and developmental disorders [27].