New phenotype of severe neonatal episodic laryngospasm due to a missense mutation in SCN4A: A case report and literature review. / 由SCN4AåŸºå› é”™ä¹‰çªå˜å¯¼è‡´çš„ä¸¥é‡æ–°ç”Ÿå„¿å‘ä½œæ€§å–‰ç—‰æŒ›1ä¾‹åŠæ–‡çŒ®å¤ä¹ .

Severe neonatal episodic laryngospasm (SNEL) is an ion channel disease characterized by recurrent life-threatening myotonia of respiratory muscle due to mutations in the voltage-gated sodium channel genes. Here we reported a newborn manifested as paroxysmal cyanosis and limb myotonia after birth. The neonate also developed muscle hypertrophy and stunted growth during the follow-up. Whole exome sequencing confirmed c.2395G>A, p.Ala799Thr heterozygous mutation of SCN4A. Carbamazepine was found to be effective on treating the disease. This case expands our understanding of the phenotype resulting from SCN4Amutations. By summarizing the characteristics of reported 16 cases in SNEL,we found they were mainly in the p.G1306E mutation. The common symptoms were upper airway muscle stiffness and feeding difficulties during neonates.When grow up, most patients have different degrees of recurrent attacks of myotonia and progressed muscle hypertrophy. Some of them have athlete-like special faces but all showed myotonic discharge in eletromyogram.

Improving genetic diagnostics of skeletal muscle channelopathies.

INTRODUCTION: Skeletal muscle channelopathies are rare inherited conditions that cause significant morbidity and impact on quality of life. Some subsets have a mortality risk. Improved genetic methodology and understanding of phenotypes have improved diagnostic accuracy and yield. AREAS COVERED: We discuss diagnostic advances since the advent of next-generation sequencing and the role of whole exome and genome sequencing. Advances in genotype-phenotype-functional correlations have improved understanding of inheritance and phenotypes. We outline new phenotypes, particularly in the pediatric setting and consider co-existing mutations that may act as genetic modifiers. We also discuss four newly identified genes associated with skeletal muscle channelopathies. EXPERT OPINION: Next-generation sequencing using gene panels has improved diagnostic rates, identified new mutations, and discovered patients with co-existing pathogenic mutations ('double trouble'). This field has previously focussed on single genes, but we are now beginning to understand interactions between co-existing mutations, genetic modifiers, and their role in pathomechanisms. New genetic observations in pediatric presentations of channelopathies broadens our understanding of the conditions. Genetic and mechanistic advances have increased the potential to develop treatments.

Myasthenic congenital myopathy from recessive mutations at a single residue in NaV1.4.

OBJECTIVE: To identify the genetic and physiologic basis for recessive myasthenic congenital myopathy in 2 families, suggestive of a channelopathy involving the sodium channel gene, SCN4A. METHODS: A combination of whole exome sequencing and targeted mutation analysis, followed by voltage-clamp studies of mutant sodium channels expressed in fibroblasts (HEK cells) and Xenopus oocytes. RESULTS: Missense mutations of the same residue in the skeletal muscle sodium channel, R1460 of NaV1.4, were identified in a family and a single patient of Finnish origin (p.R1460Q) and a proband in the United States (p.R1460W). Congenital hypotonia, breathing difficulties, bulbar weakness, and fatigability had recessive inheritance (homozygous p.R1460W or compound heterozygous p.R1460Q and p.R1059X), whereas carriers were either asymptomatic (p.R1460W) or had myotonia (p.R1460Q). Sodium currents conducted by mutant channels showed unusual mixed defects with both loss-of-function (reduced amplitude, hyperpolarized shift of inactivation) and gain-of-function (slower entry and faster recovery from inactivation) changes. CONCLUSIONS: Novel mutations in families with myasthenic congenital myopathy have been identified at p.R1460 of the sodium channel. Recessive inheritance, with experimentally established loss-of-function, is a consistent feature of sodium channel based myasthenia, whereas the mixed gain of function for p.R1460 may also cause susceptibility to myotonia.

Hypocalcaemia in an adult: the importance of not overlooking the cause.

A 58-year-old male patient was admitted at the São Bernardos's Hospital (Setúbal, Portugal) with generalised muscle spasms, dyspnoea, laryngospasm and bronchospasm in the context of severe hypocalcaemia. Despite efforts to correct serum calcium, it remained below average, leading to question the true cause of hypocalcaemia. Low parathyroid hormone and 25-hydroxyvitamin D, along with facial anomalies, palate defect and cognitive impairment with concomitant psychiatric disorder led to a suspicion of a DiGeorge/velocardiofacial/22q11.2 deletion syndrome (DS), which was confirmed through genetic testing. The 22q11.2 DS has a wide phenotypic expression and there are growing reports of diagnosis being made in adulthood. This case report highlights the importance of understanding the cause of refractory hypocalcaemia and alerts medical community to carefully access these patients, for this metabolic disorder may only present in later stages of life.

Mutations in SCN4A: a rare but treatable cause of recurrent life-threatening laryngospasm.

Laryngospasm is a rare but potentially life-threatening occurrence in infants and usually has infective, allergic, metabolic, or anatomic causes. Underlying genetic conditions are rarely considered. Mutations in SCN4A encoding the voltage-gated sodium channel NaV1.4 have been implicated in a wide spectrum of neuromuscular disorders with variable onset, ranging from a rare form of congenital myasthenic syndrome to both hypokalemic and hyperkalemic forms of periodic paralysis and paramyotonia congenita. Here we report on 3 unrelated patients without family history presenting with recurrent, life-threatening episodes of laryngospasm from the first months of life. Clinical features more typically associated with SCN4A-related disorders such as generalized muscle hypertrophy with clinical or electrical myotonia evolved later in life. All patients were found to be heterozygous for the same SCN4A mutation, c.3917G>A; p.Gly1306Glu. Treatment with carbamazepine resulted in complete abolition of recurrent laryngospasm and alleviated symptoms associated with myotonia and muscle stiffness. We conclude that SCN4A mutations ought to be considered in the differential diagnosis of recurrent infantile laryngospasm because timely institution of treatment can be life-saving.

Distinct acoustic features in spinal and bulbar muscular atrophy patients with laryngospasm.

OBJECTIVE: Laryngospasm is a sudden onset of transient respiratory difficulty that is perceived as life-threatening by patients with spinal and bulbar muscular atrophy (SBMA). The purpose of the study was to analyze the voice characteristics of SBMA patients with laryngospasm using acoustic voice analysis. METHODS: Acoustic measurements were obtained from 39 consecutive Japanese patients with genetically confirmed SBMA. A comparison was made between the acoustic voice profiles of 16 patients with laryngospasm and 23 patients without laryngospasm within 6 months before the evaluation. Computerized acoustic analysis was performed for a prolonged vowel (/a:/) using the Multi-Dimensional Voice Program (MDVP). RESULTS: SBMA patients with laryngospasm had smaller fluctuations of vocal fold vibration and the turbulent noise component, indicating stronger vocal fold closure than in those without laryngospasm. Receiver operating characteristic curve analysis showed that the noise-to-harmonic ratio, which globally measures the noise components of voice, is the most useful acoustic parameter to distinguish laryngospasm (area under the curve = 0.767, p = 0.007). CONCLUSIONS: The smaller noise component in patients with laryngospasm suggests that the vocal folds of these patients are more adducted during phonation than those of the patients without laryngospasm, even in the absence of laryngospasm. Quantitative laryngeal analysis using the MDVP helps to detect laryngeal dysfunction and provides physiological insight into the pathophysiology of laryngospasm in SBMA.

Diagnosis and outcome of SCN4A-related severe neonatal episodic laryngospasm (SNEL): 2 new cases.

Mutations of SCN4A encoding the skeletal muscle sodium channel Nav 1.4 cause several types of disease, including sodium channel myotonias. The latter may be responsible for neonatal symptoms, including severe neonatal episodic laryngospasm (SNEL). Establishing the diagnosis of SCN4A-related SNEL early in the neonatal period is crucial because treatment is available that can reduce laryngospasm and improve vital and cerebral outcome. We report 2 new unrelated French patients who presented with SNEL. The first patient was initially diagnosed with laryngomalacia and underwent laryngeal surgery in the neonatal period before being diagnosed with myotonia at 14 months of age. The episodes of laryngospasm disappeared spontaneously, although occasional circumstances such as cold exposure could trigger laryngeal reactions; in addition, he developed myotonia corresponding to an adult myotonia permanens phenotype. This patient is now 24 years old and leading a normal life. The second patient was initially diagnosed with gastroesophageal reflux, then SNEL; his condition improved with carbamazepine treatment, and he is now 6 months old. The diagnostic sequence in both patients was the same: first, severe episodic apneic attacks necessitating hospitalization occurring in the first week of life; second, observation of muscle hypertrophy and peripheral hypertonia with a clear myotonic pattern on electromyogram (at 14 and 3 months of age, respectively); third, genetic testing revealing de novo SCN4A G1306E mutation. Both patients have had good therapeutic response to sodium channel blockers (carbamazepine or mexiletine).

Mechanisms underlying a life-threatening skeletal muscle Na+ channel disorder.

Myotonia is an intrinsic muscular disorder caused by muscle fibre hyperexcitability, which produces a prolonged time for relaxation after voluntary muscle contraction or internal mechanical stimulation. Missense mutations in skeletal muscle genes encoding Cl− or Na+ channels cause non-dystrophic myotonias.Mutations of the SCN4A gene that encodes the skeletal voltage-gated Na+ channel Nav1.4 can produce opposing phenotypes leading to hyperexcitable or inexcitable muscle fibres. Nav1.4 mutations result in different forms of myotonias that can be found in adults. However, the recently reported myotonic manifestations in infants have been shown to be lethal. This was typically the case for children suffering from severe neonatal episodic laryngospasm (SNEL). A novel Nav1.4 channel missense mutation was found in these children that has not yet been analysed. In this study, we characterize the functional consequences of the new A799S Na+ channel mutation that is associated with sodium channel myotonia in newborn babies. We have used mammalian cell expression and patch-clamp techniques to monitor the channel properties.We found that the A799S substitution changes several biophysical properties of the channel by causing a hyperpolarizing shift of the steady-state activation, and slowing the kinetics of fast inactivation and deactivation. In addition, the single channel open probability was dramatically increased, contributing hence to a severe phenotype. We showed that substitutions at position 799 of the Nav1.4 channel favoured the channel open state with sustained activity leading to hyperexcitability of laryngeal muscles that could be lethal during infancy.

Severe neonatal episodic laryngospasm due to de novo SCN4A mutations: a new treatable disorder.

BACKGROUND: Myotonia is unusual in infants, and not well-known. METHODS: We describe neonatal life-threatening features of myotonia caused by de novo mutations in the muscle sodium channel gene SCN4A. RESULTS: Three male neonates initially displayed episodic laryngospasms, with face and limb myotonia appearing later. We found SCN4A de novo mutations in these neonates: p.Gly1306Glu in 2 unrelated cases and a novel mutation p.Ala799Ser in the third. Two patients survived their respiratory attacks and were efficiently treated by sodium channel blockers (mexiletine, carbamazepine) following diagnosis of myotonia. CONCLUSION: Severe neonatal episodic laryngospasm is a new phenotype caused by a sodium channelopathy, which can be alleviated by channel blockers.

Effect of high-intensity exercise on arterial blood gas tensions and upper airway and cardiac function in clinically normal quarter horses and horses heterozygous and homozygous for hyperkalemic periodic paralysis.

OBJECTIVE: To determine the effect of exercise on arterial blood gas tensions and upper airway and cardiac function in clinically normal Quarter Horses and horses heterozygous and homozygous for hyperkalemic periodic paralysis (HYPP). ANIMALS AND PROCEDURE: 5 clinically normal Quarter Horses, and 5 heterozygous and 2 homozygous HYPP-affected horses were examined before, during, and after exercise on a high-speed treadmill. Arterial blood gas tensions, ECG, and echocardiogram were obtained prior to exercise. Upper airway endoscopy, collection of arterial blood samples, and continuous electrocardiography were performed during a high-intensity stepwise exercise test. An ECG was obtained within 1-minute after completion of the final step. RESULTS: None of the horses homozygous or heterozygous for HYPP had signs of weakness or muscle fasciculations before, during, or after exercise. Horses homozygous for HYPP had intermittent laryngospasm, dynamic pharyngeal collapse, and appreciable hypoxemia, hypercapnia, and ventricular premature contractions during exercise. Heterozygous and clinically normal horses did not have any abnormalities. Potassium concentration increased significantly above the baseline reference range during exercise in all groups of horses. CONCLUSIONS: Horses homozygous for HYPP had laryngospasm and dynamic pharyngeal collapse associated with exercise, most likely secondary to increase in potassium concentration. Upper airway dysfunction is the most likely cause of hypoxemia and hypercapnia. Cardiac arrhythmias were most likely caused by a combination of hypoxemia and hyperkalemia.

Laryngeal dystonia: a series with botulinum toxin therapy.

Laryngeal dystonia is a syndrome characterized by action-induced, involuntary spasms of the laryngeal muscles. Most patients have involvement of the adductor laryngeal muscles producing uncontrolled spasms during phonation, and a "strain-strangle" speech pattern commonly termed "spastic dysphonia." Other patients have involvement of the abductor muscles producing "whispering dysphonia." Rare patients have paradoxical vocal cord motion during respiration with adductor spasms on inspiration. Over the past 5 years we have used botulinum toxin (BOTOX) to treat more than 200 patients with laryngeal dystonia. This group includes patients with adductor involvement (phonatory dystonia, recurrent laryngeal nerve section failure, respiratory dystonia) and those with abductor involvement (whispering dystonia). Patients received benefit within 24 to 72 hours, with sustained improvement for 2 to 9 months with an average of 4 months. Patients improved to an average of 90% of normal function. Clinically significant adverse effects included extended breathy dysphonia and mild choking on fluids. BOTOX has become our treatment of choice for dystonic conditions of the larynx.