Review of the Diagnosis and Treatment of Periodic Paralysis

The long exercise test as a functional marker of periodic paralysis

AIMS

The aim of this study was to evaluate the sensitivity of the long exercise test (LET) in the diagnosis of periodic paralysis (PP) and assess correlations with clinical phenotypes and genotypes.

METHODS

From an unselected cohort of 335 patients who had an LET we analyzed 67 patients with genetic confirmation of PP and/or a positive LET.

RESULTS

32/45 patients with genetically confirmed PP had a significant decrement after exercise (sensitivity of 71%). Performing the short exercise test before the LET in the same hand confounded results in four patients. Sensitivity was highest in patients with frequent (daily or weekly) attacks (8/8, 100%), intermediate with up to monthly attacks (15/21, 71%) and lowest in those with rare attacks (9/16, 56%) (p = .035, Mann-Whitney U-test). Patients with a positive LET without confirmed PP mutation comprised those with typical PP phenotype and a group with atypical features.

DISCUSSION

In our cohort, the LET is strongly correlated with the frequency of paralytic attacks suggesting a role as a functional marker. A negative test in the context of frequent attacks makes a diagnosis of PP unlikely but it does not rule out the condition in less severely affected patients.

Phenotypical variability and atypical presentations in a French cohort of Andersen-Tawil syndrome

BACKGROUND AND PURPOSE

Andersen-Tawil syndrome (ATS) is a skeletal muscle channelopathy caused by KCNJ2 mutations, characterized by a clinical triad of periodic paralysis, cardiac arrhythmias and dysmorphism. The muscle phenotype, particularly the atypical forms with prominent permanent weakness or predominantly painful symptoms, remains incompletely characterized.

METHODS

A retrospective clinical, histological, electroneuromyography (ENMG) and genetic analysis of molecularly confirmed ATS patients, diagnosed and followed up at neuromuscular reference centers in France, was conducted.

RESULTS

Thirty-five patients from 27 unrelated families carrying 17 different missense KCNJ2 mutations (four novel mutations) and a heterozygous KCNJ2 duplication are reported. The typical triad was observed in 42.9% of patients. Cardiac abnormalities were observed in 65.7%: 56.5% asymptomatic and 39.1% requiring antiarrhythmic drugs. 71.4% of patients exhibited dysmorphic features. Muscle symptoms were reported in 85.7%, amongst whom 13.3% had no cardiopathy and 33.3% no dysmorphic features. Periodic paralysis was present in 80% and was significantly more frequent in men. Common triggers were exercise, immobility and carbohydrate-rich diet. Ictal serum potassium concentrations were low in 53.6%. Of the 35 patients, 45.7% had permanent weakness affecting proximal muscles, which was mild and stable or slowly progressive over several decades. Four patients presented with exercise-induced pain and myalgia attacks. Diagnostic delay was 14.4 ± 9.5 years. ENMG long-exercise test performed in 25 patients (71.4%) showed in all a decremental response up to 40%. Muscle biopsy performed in 12 patients revealed tubular aggregates in six patients (associated in two of them with vacuolar lesions), dystrophic features in one patient and non-specific myopathic features in one patient; it was normal in four patients.

DISCUSSION

Recognition of atypical features (exercise-induced pain or myalgia and permanent weakness) along with any of the elements of the triad should arouse suspicion. The ENMG long-exercise test has a high diagnostic yield and should be performed. Early diagnosis is of utmost importance to improve disease prognosis.

In silico, in vitro, and in vivo human metabolism of acetazolamide, a carbonic anhydrase inhibitor and common "diuretic and masking agent" in doping

Acetazolamide (ACZ) is a carbonic anhydrase inhibitor prescribed for the treatment of various pathologies. It is also used in doping and is prohibited in and out of sportive competitions. ACZ was reported not to undergo metabolization. However, the detection of ACZ metabolites may be critical for documenting ACZ use. We aimed to further investigate ACZ metabolic fate in humans. ACZ putative metabolites were generated in silico to assist in metabolite identification. ACZ was incubated with primary human hepatocytes to identify in vitro metabolites (10 µmol/l ACZ and 10⁶ cells/ml), and urine and plasma samples from patients receiving a single 5.0 mg/kg BW PO ACZ dose were analyzed to confirm the results in vivo. Analyses were performed with reversed-phase liquid chromatography and hydrophilic interaction chromatography coupled with high-resolution tandem mass spectrometry (RPLC-HRMS/MS and HILIC-HRMS/MS, respectively). Data were screened with a software-assisted targeted/untargeted workflow. ACZ was quantified in urine samples with creatinine normalization. We identified two metabolites in hepatocyte incubations and three additional metabolites in urine and plasma. Major transformations included cysteine conjugation, glucuronidation, and N-acetylation. All metabolites were detected in plasma, 1.5 h after intake. Major metabolites were detected in urine from 0.25 to 24 h (last collection) after intake. As opposed to the literature, ACZ does undergo metabolization in humans. We propose ACZ, ACZ-Cys, and N-acetyl-ACZ in urine, and ACZ and N-acetyl-ACZ in plasma as specific biomarkers of ACZ intake in doping.

In vitro contractile studies within isolated tissue baths: Translational research from Visible Heart® Laboratories

The isolated tissue bath research methodology was first developed in 1904. Since then, it has been recognized as an important tool in pharmacology and physiology research, including investigations into neuromuscular disorders. The tissue bath is still used routinely as the instrument for performing the "gold standard" test for clinical diagnosis of malignant hyperthermia susceptibility - the caffeine-halothane contracture test. Our research group has utilized this tool for several decades for a range of research studies, and we are currently one of four North American diagnostic centers for determining susceptibility for malignant hyperthermia. This review provides a brief summary of some of the historical uses of the tissue bath. Important experimental considerations for the operation of the tissue bath are further described. Finally, we discuss the different studies our group has performed using isolated tissue baths to highlight the broad potential applications.

Sporadic adult-onset brainstem hyperkalemic periodic paralysis masquerading as recurrent transient ischemic attacks

We report a case of adult-onset, sporadic, hyperkalemic periodic paralysis with primary brainstem musculature symptoms masquerading as recurrent transient ischemic attacks. Unilateral brainstem weakness could be induced with rapid eye blinking, which was followed by lower extremity weakness and cramping. Treatment with acetazolamide and albuterol ameliorated the patient's attacks.

The role of nephrologists in management of hypokalemic periodic paralysis: a case report

Background

Hypokalemic periodic paralysis is a chronic condition characterized by sporadic attacks of weakness associated with acute hypokalemia. Attacks are typically associated with specific triggers, such as prolonged rest following exercise or consumption of a high-carbohydrate meal. Most commonly, this condition is caused by an autosomal dominant calcium channel mutation, and patients typically have an established family medical history of hypokalemic periodic paralysis. Long-term complications include the development of progressive proximal myopathy. Oral potassium chloride may be considered for the treatment of an acute attack, with administration of acetazolamide or dichlorphenamide as long-term prophylaxis. Nephrologists can play an important role in the recognition and treatment of previously undiagnosed hypokalemic periodic paralysis.

Case presentation

We summarize the case of a 19-year-old white man who presented to the emergency department with undiagnosed attacks of hypokalemic periodic paralysis, and who reported, at follow-up, improvement in the severity and frequency of attacks with dichlorphenamide.

Conclusions

This case demonstrates the crucial role nephrologists can play, not only in the diagnosis of hypokalemic periodic paralysis, but also in the ongoing management of this condition. Patients should be advised to regularly follow up with their nephrology team for evaluation due to the risk of developing myopathy.

Novel CACNA1S mutation in hypokalaemic periodic paralysis

A 15-year-old girl was admitted to emergency department with an acute flaccid tetraparesis with no other symptoms. A history of recurrent similar episodes with spontaneous recovery was reported and no family history was known. Laboratory tests revealed severe hypokalaemia and hypokaluria. Symptoms resolution occurred after potassium replacement. The diagnosis of hypokalaemic periodic paralysis (HPP) was confirmed by genetic testing, which revealed a not previously described mutation in CACNA1S gene (c.3715C>G p.Arg1239Gly). HPP is a rare neuromuscular disorder that causes episodic attacks of flaccid paralysis with concomitant hypokalaemia. Primary forms of the disease are skeletal muscle ion channelopathies. HPP occurs due to a problem in potassium distribution rather than a total body potassium deficiency. Therefore potassium replacement should be carefully performed because of the risk of rebound hyperkalaemia. Knowing this rare entity is important in order to avoid diagnostic delays and so that proper treatment can be initiated to reduce morbidity and mortality.

Episodic weakness and axonal sensorimotor neuropathy caused by a mitochondrial MT-ATP6 mutation

Episodic weakness is typically associated with a group of disorders so called periodic paralyses. Their major causes are mutation of ion channels, and have rarely been linked to mitochondrial disorders. We report a 20-year-old man with episodic weakness and axonal sensorimotor neuropathy since the age of 10 years. Analysis of the next generation sequencing data of the entire mitochondrial genome extracted from the blood revealed a homoplasmic m.9185T > C variant in MT-ATP6. Acetazolamide may be responsive for episodic weakness, and supplements with l-carnitine with coenzyme-Q10 seem to be beneficial as well. To the best of our knowledge, this is the first report in Taiwan which reveals episodic weakness and sensorimotor polyneuropathy as a unique phenotype of MT-ATP6 mutations.

The clinical and genetic heterogeneity analysis of five families with primary periodic paralysis

To explore the clinical and genetic characteristics of five families with primary periodic paralysis (PPP). We reviewed clinical manifestations, laboratory results, electrocardiogram, electromyography, muscle biopsy, and genetic analysis from five families with PPP. Five families with PPP included: hypokalemic periodic paralysis type 1 (HypoPP1, CACNA1S, 1/5), hypokalemic periodic paralysis type 2 (HypoPP2, SCN4A, 2/5), normokalemic periodic paralysis (NormoPP, SCN4A, 1/5), and Andersen-Tawil syndrome (ATS, KCNJ2, 1/5). The basic clinical manifestations of five families were consistent with PPP, presenting with paroxysmal muscle weakness, with or without abnormal serum potassium. ATS was accompanied by ventricular arrhythmias, and skeletal and craniofacial anomalies, developing with a permanent fixed myopathy later. The electromyography showed diffuse myopathic discharge, and muscle biopsy showed tubular aggregates. Genetic testing revealed five families with PPP carried CACNA1S (R1242S), SCN4A (R675Q, T704M), and KCNJ2 (R218Q) respectively. The novel heterozygous R1242S mutation in CACNA1S caused a conformational change in the protein structure, and the amino acid of this mutation site was highly conserved among different species. SCN4A mutations led to two phenotypes of HypoPP2 and NormoPP. PPPs are autosomal dominant disorders of ion channel dysfunction characterized by episodic flaccid muscle weakness secondary to abnormal sarcolemmal excitability. PPPs are caused by mutations in skeletal muscle calcium channel CaV1.1 gene (CACNA1S), sodium channel NaV1.4 gene (SCN4A), and potassium channels Kir2.1, Kir3.4 genes (KCNJ2, KCNJ5), including HypoPP1, HypoPP2, NormoPP, HyperPP, and ATS, which have significant clinical and genetic heterogeneity. Diagnosis is based on the characteristic clinical presentation then confirmed by genetic testing.

Case Report: A Novel CACNA1S Mutation Associated With Hypokalemic Periodic Paralysis in a Chinese Family

Hypokalemic periodic paralysis (HypoPP) is a rare autosomal dominant disorder characterized by episodic flaccid paralysis with concomitant hypokalemia. More than half of patients were associated with mutations in CACNA1S that encodes the alpha-1-subunit of the skeletal muscle L-type voltage-dependent calcium channel. Mutations in CACNA1S may alter the structure of CACNA1S and affect the functions of calcium channels, which damages Ca²⁺-mediated excitation-contraction coupling. In this research, we identified and described a Chinese HypoPP patient with a novel frameshift mutation in CACNA1S [NM_000069.2: c.1364delA (p.Asn455fs)] by targeted sequencing. This study would expand the spectrum of CACNA1S mutations, further our understanding of HypoPP, and provided a new perspective for selecting effective treatments.

KCNG1-Related Syndromic Form of Congenital Neuromuscular Channelopathy in a Crossbred Calf

Inherited channelopathies are a clinically and heritably heterogeneous group of disorders that result from ion channel dysfunction. The aim of this study was to characterize the clinicopathologic features of a Belgian Blue x Holstein crossbred calf with paradoxical myotonia congenita, craniofacial dysmorphism, and myelodysplasia, and to identify the most likely genetic etiology. The calf displayed episodes of exercise-induced generalized myotonic muscle stiffness accompanied by increase in serum potassium. It also showed slight flattening of the splanchnocranium with deviation to the right side. On gross pathology, myelodysplasia (hydrosyringomielia and segmental hypoplasia) in the lumbosacral intumescence region was noticed. Histopathology of the muscle profile revealed loss of the main shape in 5.3% of muscle fibers. Whole-genome sequencing revealed a heterozygous missense variant in KCNG1 affecting an evolutionary conserved residue (p.Trp416Cys). The mutation was predicted to be deleterious and to alter the pore helix of the ion transport domain of the transmembrane protein. The identified variant was present only in the affected calf and not seen in more than 5200 other sequenced bovine genomes. We speculate that the mutation occurred either as a parental germline mutation or post-zygotically in the developing embryo. This study implicates an important role for KCNG1 as a member of the potassium voltage-gated channel group in neurodegeneration. Providing the first possible KCNG1-related disease model, we have, therefore, identified a new potential candidate for related conditions both in animals and in humans. This study illustrates the enormous potential of phenotypically well-studied spontaneous mutants in domestic animals to provide new insights into the function of individual genes.

Mind the Gap: Acetazolamide Prolonged Periods without Paralysis in a Girl with Andersen-Tawil Syndrome

We present a case report of a 13-year-old girl with Andersen-Tawil Syndrome (ATS), a rare genetic disorder which is characterized by dysmorphic features, ventricular arrhythmias, and frequent episodes of muscle paralysis that interfere with daily activities and social engagement. After the introduction of off-label treatment with acetazolamide periods without paralysis lengthened, our patient became more independent of the help of her parents and required a wheelchair less frequently, thus improving her social life. Based on our experience, we recommend a trial of acetazolamide in patients with ATS.

New Challenges Resulting From the Loss of Function of Nav1.4 in Neuromuscular Diseases

The voltage-gated sodium channel Na_v1.4 is a major actor in the excitability of skeletal myofibers, driving the muscle force in response to nerve stimulation. Supporting further this key role, mutations in SCN4A, the gene encoding the pore-forming α subunit of Na_v1.4, are responsible for a clinical spectrum of human diseases ranging from muscle stiffness (sodium channel myotonia, SCM) to muscle weakness. For years, only dominantly-inherited diseases resulting from Na_v1.4 gain of function (GoF) were known, i.e., non-dystrophic myotonia (delayed muscle relaxation due to myofiber hyperexcitability), paramyotonia congenita and hyperkalemic or hypokalemic periodic paralyses (episodic flaccid muscle weakness due to transient myofiber hypoexcitability). These last 5 years, SCN4A mutations inducing Na_v1.4 loss of function (LoF) were identified as the cause of dominantly and recessively-inherited disorders with muscle weakness: periodic paralyses with hypokalemic attacks, congenital myasthenic syndromes and congenital myopathies. We propose to name this clinical spectrum sodium channel weakness (SCW) as the mirror of SCM. Na_v1.4 LoF as a cause of permanent muscle weakness was quite unexpected as the Na⁺ current density in the sarcolemma is large, securing the ability to generate and propagate muscle action potentials. The properties of SCN4A LoF mutations are well documented at the channel level in cellular electrophysiological studies However, much less is known about the functional consequences of Na_v1.4 LoF in skeletal myofibers with no available pertinent cell or animal models. Regarding the therapeutic issues for Na_v1.4 channelopathies, former efforts were aimed at developing subtype-selective Na_v channel antagonists to block myofiber hyperexcitability. Non-selective, Na_v channel blockers are clinically efficient in SCM and paramyotonia congenita, whereas patient education and carbonic anhydrase inhibitors are helpful to prevent attacks in periodic paralyses. Developing therapeutic tools able to counteract Na_v1.4 LoF in skeletal muscles is then a new challenge in the field of Na_v channelopathies. Here, we review the current knowledge regarding Na_v1.4 LoF and discuss the possible therapeutic strategies to be developed in order to improve muscle force in SCW.

[17-year-old patient with polymorphic premature ventricular contractions]

A 17-year-old patient with premature ventricular contractions and normal left ventricular function was referred for reablation after an unsuccessful catheter ablation attempt. Holter monitoring demonstrated a high burden of premature ventricular contractions, present throughout the whole recording. The patient reported occasional paralytic attacks; his face had a dysmorphic appearance with a wide distance between the eyes, a caudal insertion of the ears, and a high forehead. These three features resulted in a clinical diagnosis that was confirmed by molecular biology and completely changed the therapeutic strategy.

Mutations associated with hypokalemic periodic paralysis: from hotspot regions to complete analysis of CACNA1S and SCN4A genes

Familial periodic paralyses (PPs) are inherited disorders of skeletal muscle characterized by recurrent episodes of flaccid muscle weakness. PPs are classified as hypokalemic (HypoPP), normokalemic (NormoPP), or hyperkalemic (HyperPP) according to the potassium level during the paralytic attacks. HypoPP is an autosomal dominant disease caused by mutations in the CACNA1S gene, encoding for Cav1.1 channel (HypoPP-1), or SCN4A gene, encoding for Nav1.4 channel (HypoPP-2). In the present study, we included 60 patients with a clinical diagnosis of HypoPP. Fifty-one (85%) patients were tested using the direct sequencing (Sanger method) of all reported HypoPP mutations in CACNA1S and SCN4A genes; the remaining 9 (15%) patients were analyzed through a next-generation sequencing (NGS) panel, including the whole CACNA1S and SCN4A genes, plus other genes rarely associated to PPs. Fifty patients resulted mutated: 38 (76%) cases showed p.R528H and p.R1239G/H CACNA1S mutations and 12 (24%) displayed p.R669H, p.R672C/H, p.R1132G/Q, and p.R1135H SCN4A mutations. Forty-one mutated cases were identified among the 51 patients managed with Sanger sequencing, while all the 9 cases directly analyzed with the NGS panel showed mutations in the hotspot regions of SCN4A and CACNA1S. Ten out of the 51 patients unresolved through the Sanger sequencing were further analyzed with the NGS panel, without the detection of any mutation. Hence, our data suggest that in HypoPP patients, the extension of genetic analysis from the hotspot regions using the Sanger method to the NGS sequencing of the entire CACNA1S and SCN4A genes does not lead to the identification of new pathological mutations.

Co-existence of Congenital Adrenal Hyperplasia and Familial Hypokalemic Periodic Paralysis due to CYP21A2 and SCN4A Pathogenic Variants

Steroid 21-hydroxylase deficiency is the most common cause of congenital adrenal hyperplasia (CAH), usually due to biallelic variants in CYP21A2. Classical 21-hydroxylase deficiency is characterised by virilisation of the external genitalia in females and hypocortisolism. Hyponatremia and hyperkalemia are among the common biochemical findings. Familial hypokalemic periodic paralysis (FHPP) is a rare disorder in which affected individuals may experience paralytic episodes associated with hypokalemia, caused by pathogenic variants in SCN4A or CACNA1S. A 14-year-old female, who had been diagnosed with classical 21-hydroxylase deficiency and treated with hydrocortisone and fludrocortisone since early infancy, presented with acute onset weakness. The laboratory results revealed a remarkably low serum potassium level. The family history revealed that both her father and uncle had the same hypokalemic symptoms, which suggested an FHPP diagnosis. We found two previously reported homozygous variants in the CYP21A2 (p.Ile173Asn) and SCN4A (p.Arg672His) genes in the patient. Therefore, diagnoses of simple virilising 21-hydroxylase deficiency and FHPP were genetically confirmed. Here, FPHH and chronic overtreatment with fludrocortisone may explain the presentation of our patient with severe hypokalemia. The family’s medical history, which is always a valuable clue, should be investigated in detail since rare inherited conditions may co-occur in geographies where consanguineous marriages are common and the genetic pool is diverse. In patients with CAH, care should be taken to avoid overtreatment with fludrocortisone. Androgens may have triggered the hypokalemic attack in FHPP, as supported in a previous study.

19-year-old Woman with Intermittent Weakness

Introduction

Systemic weakness is a common chief complaint of patients presenting to the emergency department (ED). A well thought out approach to the assessment and workup of these patients is key to diagnostic accuracy and definitive therapy.

Case Presentation

In this case, a 19-year-old female presented to the ED with generalized weakness and near syncope. She had global weakness in her extremities and multiple electrolyte abnormalities.

Discussion

This case takes the reader through the differential diagnosis and evaluation of a patient with weakness and profound electrolyte derangements. It includes a discussion of the diagnostic studies and calculations that ultimately led to the patient’s diagnosis.

E-Health & Innovation to Overcome Barriers in Neuromuscular Diseases. Report from the 1st eNMD Congress: Nice, France, March 22-23, 2019

By definition, neuromuscular diseases are rare and fluctuating in terms of symptoms; patients are often lately diagnosed, do not have enough information to understand their condition and be proactive in their management. Usually, insufficient resources or services are available, leading to patients' social burden. From a medical perspective, the rarity of such diseases leads to the unfamiliarity of the medical staff and caregiver and an absence of consensus in disease assessment, treatment, and management. Innovations have to be developed in response to patients' and physicians' unmet needs.It is vital to improve several aspects of patients' quality of life with a better comprehension of their disease, simplify their management and follow-up, help their caregiver, and reduce the social and economic burden for living with a rare debilitating disease. Database construction regrouping patients' data and symptoms according to specific country registration on data privacy will be critical in establishing a clear consensus on neuromuscular disease treatment.Clinicians also need technological innovations to help them recognize neuromuscular diseases, find the best therapeutic approach based on medical consensus, and tools to follow patients' states regularly. Diagnosis also has to be improved by implementing automated systems to analyze a considerable amount of data, representing a significant step forward to accelerate the diagnosis and the patients' follow up. Further, the development of new tools able to precisely measure specific outcomes reliably is of the matter of importance in clinical trials to assess the efficacy of a newly developed compound.In this context, creation of an expert community is essential to communicate and share ideas. To this end, 97 clinicians, healthcare professionals, researchers, and representatives of private companies from 9 different countries met to discuss the new perspective and challenges to develop and implement innovative tools in the field of neuromuscular diseases.

The Role of Nutrition and Physical Activity as Trigger Factors of Paralytic Attacks in Primary Periodic Paralysis

Background:

Primary periodic paralysis (PPP) are rare inherited neuromuscular disorders including Hypokalemic periodic paralysis (HypoPP), Hyperkalemic periodic paralysis (HyperPP) and Andersen-Tawil syndrome (ATS) characterised by attacks of weakness or paralysis of skeletal muscles. Limited effective pharmacological treatments are available, and avoidance of lifestyle related triggers seems important.

Objective:

Our aim was to search and assess the scientific literature for information on trigger factors related to nutrition and physical activity in PPP.

Methods:

We searched Ovid Medline and Embase database for scientific papers published between January 1, 1990, to January 31, 2020.

Results:

We did not identify published observation or intervention studies evaluating effect of lifestyle changes on attacks. Current knowledge is based on case-reports, expert opinions, and retrospective case studies with inadequate methods for description of nutrition and physical activity. In HypoPP, high carbohydrate and salt intake, over-eating, alcohol, dehydration, hard physical activity, and rest after exercise are frequently reported triggers. Regarding HyperPP, fasting, intake of potassium, alcohol, cold foods or beverages, physical activity, and rest after exercise are frequently reported triggers. No nutrition related triggers are reported regarding ATS, exercise can however induce ventricular arrhythmias.

Conclusions:

Our results support that dietary intake and physical activity may play a role in causing paralytic attacks in PPP, although the current scientific evidence is weak. To provide good evidence-based patient care, several lifestyle aspects need to be further assessed and described.

Confirming Genetic Abnormalities of Hypokalemic Periodic Paralysis Using Next-Generation Sequencing: A Case Report and Literature Review

Hypokalemic periodic paralysis (hypoPP) is a disorder characterized by episodic, short-lived, and hypo-reflexive skeletal muscle weakness. HypoPP is a rare disease caused by genetic mutations related to expression of sodium or calcium ion channels. Most mutations are associated with autosomal dominant inheritance, but some are found in patients with no relevant family history. A 28-year-old man who visited the emergency room for paralytic attack was assessed in this study. He exhibited motor weakness in four limbs. There was no previous medical history or family history. The initial electrocardiogram showed a flat T wave and QT prolongation. His blood test was delayed, and sudden hypotension and bradycardia were observed. The blood test showed severe hypokalemia. After correcting hypokalemia, his muscle paralysis recovered without any neurological deficits. The patient's thyroid function and long exercise test results were normal. However, because of the history of high carbohydrate diet and exercise, hypoPP was suspected. Hence, next-generation sequencing (NGS) was performed, and a mutation of Arg669His was noted in the SCN4A gene. Although hypoPP is a rare disease, it can be suspected in patients with hypokalemic paralysis, and iden tification of this condition is important for preventing further attacks and improving patient outcomes. Diagnosing hypoPP through targeted NGS is a cost-effective and useful method.

Long-term efficacy and safety of dichlorphenamide for treatment of primary periodic paralysis

INTRODUCTION/AIM

Long-term efficacy and safety of dichlorphenamide (DCP) were characterized in patients with primary periodic paralysis (PPP).

METHODS

Patients with PPP in a double-blind, placebo-controlled study were randomly assigned to receive DCP 50 mg twice daily or placebo for 9 weeks, followed by a 52-week open-label DCP treatment phase (DCP/DCP and placebo/DCP populations). Efficacy (attack rate, severity-weighted attack rate) and safety were assessed in patients completing the study (61 weeks). In this post hoc analysis, efficacy and safety data were pooled from hyperkalemic and hypokalemic substudies.

RESULTS

Sixty-three adults (age, 19-76 years) completed the double-blind phase; 47 (74.6%) of these patients completed 61 weeks. There were median decreases in weekly attack and severity-weighted attack rates from baseline to week 61 (DCP/DCP [n = 25], -1.00 [P < .0001]; placebo/DCP [n = 20], -0.63 [P = .01] and DCP/DCP, -2.25 [P < .0001]; placebo/DCP, -1.69 [P = .01]). Relatively smaller median decreases in weekly attack and severity-weighted attack rates occurred from weeks 9 to 61 among patients receiving DCP continuously (n = 26; -0.14 [P = .1] and -0.24 [P = .09]) than among those switching from placebo to DCP after 9 weeks (n = 16; -1.04 [P = .049] and -2.72 [P = .08]). Common adverse events (AEs) were paresthesia and cognition-related events, which typically first occurred within 1 month of blinded treatment initiation and in rare cases led to treatment discontinuation. Dose reductions were frequently associated with common AE resolution.

DISCUSSION

One-year open-label DCP treatment after a 9-week randomized, controlled study confirmed long-term DCP remains safe and effective for chronic use. Tolerability issues (paresthesia, cognition-related AEs) were manageable in most patients.

Ion Channel Gene Mutations Causing Skeletal Muscle Disorders: Pathomechanisms and Opportunities for Therapy

Skeletal muscle ion channelopathies (SMICs) are a large heterogeneous group of rare genetic disorders caused by mutations in genes encoding ion channel subunits in the skeletal muscle mainly characterized by myotonia or periodic paralysis, potentially resulting in long-term disabilities. However, with the development of new molecular technologies, new genes and new phenotypes, including progressive myopathies, have been recently discovered, markedly increasing the complexity in the field. In this regard, new advances in SMICs show a less conventional role of ion channels in muscle cell division, proliferation, differentiation, and survival. Hence, SMICs represent an expanding and exciting field. Here, we review current knowledge of SMICs, with a description of their clinical phenotypes, cellular and molecular pathomechanisms, and available treatments.

Nampt controls skeletal muscle development by maintaining Ca2+ homeostasis and mitochondrial integrity

Objective

NAD⁺ is a co-factor and substrate for enzymes maintaining energy homeostasis. Nicotinamide phosphoribosyltransferase (NAMPT) controls NAD⁺ synthesis, and in skeletal muscle, NAD⁺ is essential for muscle integrity. However, the underlying molecular mechanisms by which NAD⁺ synthesis affects muscle health remain poorly understood. Thus, the objective of the current study was to delineate the role of NAMPT-mediated NAD⁺ biosynthesis in skeletal muscle development and function.

Methods

To determine the role of Nampt in muscle development and function, we generated skeletal muscle-specific Nampt KO (SMNKO) mice. We performed a comprehensive phenotypic characterization of the SMNKO mice, including metabolic measurements, histological examinations, and RNA sequencing analyses of skeletal muscle from SMNKO mice and WT littermates.

Results

SMNKO mice were smaller, with phenotypic changes in skeletal muscle, including reduced fiber area and increased number of centralized nuclei. The majority of SMNKO mice died prematurely. Transcriptomic analysis identified that the gene encoding the mitochondrial permeability transition pore (mPTP) regulator Cyclophilin D (Ppif) was upregulated in skeletal muscle of SMNKO mice from 2 weeks of age, with associated increased sensitivity of mitochondria to the Ca²⁺-stimulated mPTP opening. Treatment of SMNKO mice with the Cyclophilin D inhibitor, Cyclosporine A, increased membrane integrity, decreased the number of centralized nuclei, and increased survival.

Conclusions

Our study demonstrates that NAMPT is crucial for maintaining cellular Ca²⁺ homeostasis and skeletal muscle development, which is vital for juvenile survival.

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NAD⁺ salvage capacity is important for skeletal muscle development and survival.

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Skeletal muscle-specific Nampt knockout mice exhibit a dystrophy-like phenotype.

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Nampt deletion alters Ca²⁺ homeostasis and impairs mitochondrial function.

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Low NAD⁺ levels signals mitochondrial permeability transition pore opening.

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Cyclosporin A treatment improves sarcolemma integrity and increases survival rate.

Marked reduction in paralytic attacks in a patient with Andersen-Tawil syndrome switched from acetazolamide to dichlorphenamide

Andersen-Tawil syndrome is a rare, autosomal dominant, multisystem disorder for which the majority of cases are caused by pathogenic variants in the KCNJ2 gene. The syndrome is characterized by the clinical triad of episodic paralysis, cardiac conduction abnormalities, and dysmorphic facial and skeletal features. Treatment of Andersen-Tawil syndrome is primarily focused on management of cardiac arrhythmias and preventive management of paralytic attacks. Dichlorphenamide is approved by the US Food and Drug Administration for use in primary periodic paralysis based on several randomized, controlled trials but has not been studied in patients with Andersen-Tawil syndrome. Here, we report a case of the syndrome caused by a de novo pathogenic variant in the KCNJ2 gene (c.95_98del). The paralytic attack rate for this patient was better controlled with dichlorphenamide compared with acetazolamide, further supporting the use of dichlorphenamide in patients with Andersen-Tawil syndrome.

Appeared inexplicable disorders of consciousness after general anesthesia tracheal tube drawing in endoscopic tympanoplasty

Background

Disorders of consciousness (DOC) are neurocognitive disorders related to sharp fluctuations of attention and consciousness, while DOC is characterized by significant interindividual differences, rapid development, and a higher lethal rate.

Case information

A 53-year-old female patient underwent general anesthesia with tracheal intubation in otoendoscopic tympanoplasty. The patient suddenly appeared moderate DOC after tracheal tube removal with K+ 3.6 (3.5-5.3 mmol/L). Based on the ancillary testing and routine laboratory workup, the possible causes of DOC, such as general anesthesia drugs and cardio cerebral events, were temporarily excluded. DOC was reversed by intravenous administration of KCl 1 g, with K+ 3.78 mmol/L. On one day after surgery, the patient occurred suddenly DOC again after intravenous guttae of 5% glucose 1000 ml, K+ 3.87 mmol/L, possibly because of her recurrent hypokalemic paralysis (HP) of past medical history. The patient's consciousness gradually improved after effective KCl supplementation therapy.

Conclusion

DOC caused by periodic paralysis (PP) has not been reported, we speculate that hypoactive DOC is closely correlated with normokalemic periodic paralysis (NormoPP) in this case.

Skeletal muscle channelopathies: a guide to diagnosis and management

Skeletal muscle channelopathies are a group of rare episodic genetic disorders comprising the periodic paralyses and the non-dystrophic myotonias. They may cause significant morbidity, limit vocational opportunities, be socially embarrassing, and sometimes are associated with sudden cardiac death. The diagnosis is often hampered by symptoms that patients may find difficult to describe, a normal examination in the absence of symptoms, and the need to interpret numerous tests that may be normal or abnormal. However, the symptoms respond very well to holistic management and pharmacological treatment, with great benefit to quality of life. Here, we review when to suspect a muscle channelopathy, how to investigate a possible case and the options for therapy once a diagnosis is made.

Pediatric Paroxysmal Exercise-Induced Neurological Symptoms: Clinical Spectrum and Diagnostic Algorithm

Paroxysmal exercise-induced neurological symptoms (PENS) encompass a wide spectrum of clinical phenomena commonly presenting during childhood and characteristically elicited by physical exercise. Interestingly, few shared pathogenetic mechanisms have been identified beyond the well-known entity of paroxysmal exercise-induced dyskinesia, PENS could be part of more complex phenotypes including neuromuscular, neurodegenerative, and neurometabolic disease, epilepsies, and psychogenetic disorders. The wide and partially overlapping phenotypes and the genetic heterogeneity make the differential diagnosis frequently difficult and delayed; however, since some of these disorders may be treatable, a prompt diagnosis is mandatory. Therefore, an accurate characterization of these symptoms is pivotal for orienting more targeted biochemical, radiological, neurophysiological, and genetic investigations and finally treatment. In this article, we review the clinical, genetic, pathophysiologic, and therapeutic landscape of paroxysmal exercise induced neurological symptoms, focusing on phenomenology and differential diagnosis.

A Case of Hypokalemic Periodic Paralysis in a Young Athlete

Hypokalemic periodic paralysis (HPP) is one of the group muscle disorders that can cause sudden onset paresis or paralysis. It is a quite rare, yet, potentially life-threatening condition that, if appropriately and promptly diagnosed and treated, can be completely reversed. Other forms of periodic paralysis include thyrotoxic periodic paralysis, hyperkalemic periodic paralysis, and Anderson syndrome. We are presenting a case of a young male who presented to the emergency department (ED) with sudden paralysis to shed light on such a diagnosis and on other differential diagnoses.

Increased sarcolemma chloride conductance as one of the mechanisms of action of carbonic anhydrase inhibitors in muscle excitability disorders

To get insight into the mechanism of action of carbonic anhydrase inhibitors (CAI) in neuromuscular disorders, we investigated effects of dichlorphenamide (DCP) and acetazolamide (ACTZ) on ClC-1 chloride channels and skeletal muscle excitability. We performed patch-clamp experiments to test drugs on chloride currents in HEK293T cells transfected with hClC-1. Using the two-intracellular microelectrode technique in current-clamp mode, we measured the effects of drugs on the resting chloride conductance and action potential properties of sarcolemma in rat and mouse skeletal muscle fibers. Using BCECF dye fluorometry, we measured the effects of ACTZ on intracellular pH in single rat muscle fibers. Similarly to ACTZ, DCP (100 μM) increased hClC-1 chloride currents in HEK cells, because of the negative shift of the open probability voltage dependence and the slowing of deactivation kinetics. Bendroflumethiazide (BFT, 100 μM), structurally related to DCP but lacking activity on carbonic anhydrase, had little effects on chloride currents. In isolated rat muscle fibers, 50-100 μM of ACTZ or DCP, but not BFT, induced a ~ 20% increase of the resting chloride conductance. ACTZ reduced action potential firing in mouse muscle fibers. ACTZ (100 μM) reduced intracellular pH to 6.8 in rat muscle fibers. These results suggest that carbonic anhydrase inhibitors can reduce muscle excitability by increasing ClC-1 channel activity, probably through intracellular acidification. Such a mechanism may contribute in part to the clinical effects of these drugs in myotonia and other muscle excitability disorders.

The mechanism underlying transient weakness in myotonia congenita

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 Ca2+ currents contribute to plateau potentials. Na+ persistent inward current (NaPIC) through NaV1.4 channels is the key trigger of plateau potentials and current through CaV1.1 Ca2+ 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.

Clinical and genetic spectrum of a Chinese cohort with SCN4A gene mutations

Skeletal muscle sodium channelopathies due to SCN4A gene mutations have a broad clinical spectrum. However, each phenotype has been reported in few cases of Chinese origin. We present detailed phenotype and genotype data from a cohort of 40 cases with SCN4A gene mutations seen in neuromuscular diagnostic service in Huashan hospital, Fudan University. Cases were referred from 6 independent provinces from 2010 to 2018. A questionnaire covering demographics, precipitating factors, episodes of paralysis and myotonia was designed to collect the clinical information. Electrodiagnostic studies and muscle MRI were retrospectively analyzed. The clinical spectrum of patients included: 6 Hyperkalemic periodic paralysis (15%), 18 Hypokalemic periodic paralysis (45%), 7 sodium channel myotonia (17.5%), 4 paramyotonia congenita (10%) and 5 heterozygous asymptomatic mutation carriers (12.5%). Review of clinical information highlights a significant delay to diagnosis (median 15 years), reports of pain and myalgia in the majority of patients, male predominance, circadian rhythm and common precipitating factors. Electrodiagnostic studies revealed subclinical myotonic discharges and a positive long exercise test in asymptomatic carriers. Muscle MRI identified edema and fatty infiltration in gastrocnemius and soleus. A total of 13 reported and 2 novel SCN4A mutations were identified with most variants distributed in the transmembrane helix S4 to S6, with a hotspot mutation p.Arg675Gln accounting for 32.5% (13/40) of the cohort. Our study revealed a higher proportion of periodic paralysis in SCN4A-mutated patients compared with cohorts from England and the Netherlands. It also highlights the importance of electrodiagnostic studies in diagnosis and segregation studies.

Hypokalemic Periodic Paralysis Masquerading as a Compressive Neuraxial Lesion Following Lumbar Epidural Placement in a Parturient: A Case Report

We report the management of a parturient with undiagnosed hypokalemic periodic paralysis (HOKPP) who underwent epidural analgesia for labor, complicated by an unintentional dural puncture, and the eventual use of epidural anesthesia for cesarean delivery. Following discharge, she represented with lower extremity paresis. After being evaluated for a compressive neuraxial lesion, she made a full recovery following potassium repletion. The obstetric anesthetic implications for patients with HOKPP and how this disorder impacts the evaluation of acute motor weakness in the immediate postpartum period in a patient who recently received a neuraxial procedure are discussed.

Inherited Neuromuscular Disorders: Which Role for Serum Biomarkers?

Inherited neuromuscular disorders (INMD) are a heterogeneous group of rare diseases that involve muscles, motor neurons, peripheral nerves or the neuromuscular junction. Several different lab abnormalities have been linked to INMD: sometimes they are typical of the disorder, but they usually appear to be less specific. Sometimes serum biomarkers can point out abnormalities in presymtomatic or otherwise asymptomatic patients (e.g., carriers). More often a biomarker of INMD is evaluated by multiple clinicians other than expert in NMD before the diagnosis, because of the multisystemic involvement in INMD. The authors performed a literature search on biomarkers in inherited neuromuscular disorders to provide a practical approach to the diagnosis and the correct management of INMD. A considerable number of biomarkers have been reported that support the diagnosis of INMD, but the role of an expert clinician is crucial. Hence, the complete knowledge of such abnormalities can accelerate the diagnostic workup supporting the referral to specialists in neuromuscular disorders.

Acute non-traumatic tetraparesis - Differential diagnosis

INTRODUCTION

Potentially life-threatening disorders may present in the emergency department with acute tetraparesis, and their recognition is crucial for an appropriate management and timely treatment. Our review aims to systematize the differential diagnosis of acute non-traumatic tetraparesis.

RESULTS

Causes of tetraparesis can be classified based on the site of defect: upper motor neuron (UMN), peripheral nerve, neuromuscular junction or muscle. History of present illness should include the distribution of weakness (symmetric/asymmetric or distal/proximal/diffuse) and associated clinical features (pain, sensory findings, dysautonomia, and cranial nerve abnormalities such as diplopia and dysphagia). Neurological examination, particularly tendon reflexes, helps further in the localization of nerve lesions and distinction between UMN and lower motor neuron. Ancillary studies include blood and cerebral spinal fluid analysis, neuroaxis imaging, electromyography, muscle magnetic resonance and muscle biopsy.

CONCLUSIONS

Acute tetraparesis is still a debilitating and potentially serious neurological condition. Despite all the supplementary ancillary tests, the neurological examination is the key to achieve a correct diagnosis. The identification of life-threatening neurologic disorders is pivotal, since failing to identify patients at risk of complications, such as acute respiratory failure, may have catastrophic results.

Anaesthesia challenges of a parturient with paramyotonia congenita and terminal filum lipoma presenting for labour and caesarean section under epidural anaesthesia - a case report

Background

Paramyotonia congenita is a rare autosomal dominant myopathy which presents with periodic weakness due to cold and exercise. It is caused by mutations of the SCN4 gene which encodes the sodium channel in skeletal muscles.

Case presentation

We report a full term obstetric patient with both paramyotonia congenita and terminal filum lipoma who presents for induction of labour followed by an emergency caesarean section performed under epidural anesthesia. Her recovery is subsequently complicated by a 3-day history of postpartum paraparesis attributed to hypokalemic periodic paralysis.

Conclusion

We describe the perioperative anesthesia considerations and challenges in this case with a review of the current literature. This case report highlights the importance of early proactive and collaborative multidisciplinary approach, maintaining normal temperature and electrolytes with a heightened vigilance for muscle-related perioperative complications.

Neurological complications of cardiomyopathies

There is a multifaceted relationship between the cardiomyopathies and a wide spectrum of neurological disorders. Severe acute neurological events, such as a status epilepticus and aneurysmal subarachnoid hemorrhage, may result in an acute cardiomyopathy the likes of Takotsubo cardiomyopathy. Conversely, the cardiomyopathies may result in a wide array of neurological disorders. Diagnosis of a cardiomyopathy may have already been established at the time of the index neurological event, or the neurological event may have prompted subsequent cardiac investigations, which ultimately lead to the diagnosis of a cardiomyopathy. The cardiomyopathies belong to one of the many phenotypes of complex genetic diseases or syndromes, which may also involve the central or peripheral nervous systems. A number of exogenous agents or risk factors such as diphtheria, alcohol, and several viruses may result in secondary cardiomyopathies accompanied by several neurological manifestations. A variety of neuromuscular disorders, such as myotonic dystrophy or amyloidosis, may demonstrate cardiac involvement during their clinical course. Furthermore, a number of genetic cardiomyopathies phenotypically incorporate during their clinical evolution, a gamut of neurological manifestations, usually neuromuscular in nature. Likewise, neurological complications may be the result of diagnostic procedures or medications for the cardiomyopathies and vice versa. Neurological manifestations of the cardiomyopathies are broad and include, among others, transient ischemic attacks, ischemic strokes, intracranial hemorrhages, syncope, muscle weakness and atrophy, myotonia, cramps, ataxia, seizures, intellectual developmental disorder, cognitive impairment, dementia, oculomotor palsies, deafness, retinal involvement, and headaches.

Targeted Therapies for Skeletal Muscle Ion Channelopathies: Systematic Review and Steps Towards Precision Medicine

BACKGROUND

Skeletal muscle ion channelopathies include non-dystrophic myotonias (NDM), periodic paralyses (PP), congenital myasthenic syndrome, and recently identified congenital myopathies. The treatment of these diseases is mainly symptomatic, aimed at reducing muscle excitability in NDM or modifying triggers of attacks in PP.

OBJECTIVE

This systematic review collected the evidences regarding effects of pharmacological treatment on muscle ion channelopathies, focusing on the possible link between treatments and genetic background.

METHODS

We searched databases for randomized clinical trials (RCT) and other human studies reporting pharmacological treatments. Preclinical studies were considered to gain further information regarding mutation-dependent drug effects. All steps were performed by two independent investigators, while two others critically reviewed the entire process.

RESULTS

For NMD, RCT showed therapeutic benefits of mexiletine and lamotrigine, while other human studies suggest some efficacy of various sodium channel blockers and of the carbonic anhydrase inhibitor (CAI) acetazolamide. Preclinical studies suggest that mutations may alter sensitivity of the channel to sodium channel blockers in vitro, which has been translated to humans in some cases. For hyperkalemic and hypokalemic PP, RCT showed efficacy of the CAI dichlorphenamide in preventing paralysis. However, hypokalemic PP patients carrying sodium channel mutations may have fewer benefits from CAI compared to those carrying calcium channel mutations. Few data are available for treatment of congenital myopathies.

CONCLUSIONS

These studies provided limited information about the response to treatments of individual mutations or groups of mutations. A major effort is needed to perform human studies for designing a mutation-driven precision medicine in muscle ion channelopathies.

Andersen-Tawil Syndrome With Novel Mutation in KCNJ2: Case Report

Andersen-Tawil syndrome (ATS) is a rare autosomal dominant disorder characterized by a classic symptom triad: periodic paralysis, ventricular arrhythmias associated with prolonged QT interval, and dysmorphic skeletal and facial features. Pathogenic variants of the inwardly rectifying potassium channel subfamily J member 2 (KCNJ2) gene have been linked to the ATS. Herein, we report a novel KCNJ2 causative variant in a proband and her father showing different ATS-associated symptoms. A 15-year-old girl was referred because of episodic weakness and periodic paralysis in both legs for 2-3 months. The symptoms occurred either when she was tired or after strenuous exercise. These attacks made walking or climbing stairs difficult and lasted from one to several days. She had a short stature (142 cm, <3rd percentile) and weighed 40 kg. The proband also showed orbital hypertelorism, dental crowding, mandibular hypoplasia, fifth-digit clinodactyly, and small hands. Scoliosis in the thoracolumbar region was detected by chest X-ray. Since she was 7 years old, she had been treated for arrhythmia-associated long QT interval and underwent periodic echocardiography. Brain MRI revealed cerebrovascular abnormalities indicating absence or hypoplasia of bilateral internal carotid arteries, and compensation of other collateral vessels was observed. There were no specific findings related to intellectual development. The proband's father also had a history of periodic paralysis similar to the proband. He did not show any cardiac symptoms. Interestingly, he was diagnosed with hyperthyroidism during an evaluation for paralytic symptoms. Clinical exome sequencing revealed a novel heterozygous missense variant: Chr17(GRCh37):g.68171593A>T, NM_000891.2:c.413A>T, p.(Glu138Val) in KCNJ2 in the proband and the proband's father.

Distinctive facial features in Andersen-Tawil syndrome: A three-dimensional stereophotogrammetric analysis

Andersen-Tawil syndrome (ATS) is a rare potassium channelopathy causing periodic paralysis, cardiac arrhythmias, and dysmorphic features. A detailed analysis of the face could facilitate diagnosis of ATS, as approximately 30% of patients do not show variants in KCNJ2 gene, and diagnosis is established by clinical findings. We aimed to characterize the face in ATS through a quantitative approach, as facial anomalies may be unnoticed on visual inspection. Facial images of 12 subjects with genetically confirmed ATS (six males, six females, age 5-67 years) were acquired through stereophotogrammetry. Using 38 soft-tissue landmarks, linear distances, angles, and ratios were calculated and expressed as z-score values, with reference to 477 healthy subjects matched for sex and age. All patients showed decreased lower facial height with shortening of philtrum (mean z-score ± SD: -1.5 ± 0.9), smaller mid and lower facial depths (-1.9 ± 0.7; -2.3 ± 0.9), short palpebral fissures (right -1.2 ± 0.4; left -1.6 ± 0.6), smaller mandibular ramus length (-2.1 ± 0.4), and increased nasal width/length ratio (1.4 ± 0.5) with smaller nostril axis length (right -1.8 ± 0.8, left -1.6 ± 0.7). Hypertelorism and low-set ears were detected in two-thirds of patients. The study quantified facial dysmorphysm in ATS, extending information about known features, and detecting unrecorded philtrum and nostril characteristics, which may be distinctive traits of the disorder.

Next-generation sequencing application to investigate skeletal muscle channelopathies in a large cohort of Italian patients

Non-dystrophic myotonias and periodic paralyses are a heterogeneous group of disabling diseases classified as skeletal muscle channelopathies. Their genetic characterization is essential for prognostic and therapeutic purposes; however, several genes are involved. Sanger-based sequencing of a single gene is time-consuming, often expensive; thus, we designed a next-generation sequencing panel of 56 putative candidate genes for skeletal muscle channelopathies, codifying for proteins involved in excitability, excitation-contraction coupling, and metabolism of muscle fibres. We analyzed a large cohort of 109 Italian patients with a suspect of NDM or PP by next-generation sequencing. We identified 24 patients mutated in CLCN1 gene, 15 in SCN4A, 3 in both CLCN1 and SCN4A, 1 in ATP2A1, 1 in KCNA1 and 1 in CASQ1. Eight were novel mutations: p.G395Cfs*32, p.L843P, p.V829M, p.E258E and c.1471+4delTCAAGAC in CLCN1, p.K1302R in SCN4A, p.L208P in ATP2A1 and c.280-1G>C in CASQ1 genes. This study demonstrated the utility of targeted next generation sequencing approach in molecular diagnosis of skeletal muscle channelopathies and the importance of the collaboration between clinicians and molecular geneticists and additional methods for unclear variants to make a conclusive diagnosis.