Congenital myasthenic syndrome due to choline acetyltransferase mutations in infants: clinical suspicion and comprehensive electrophysiological assessment are important for early diagnosis

Mild phenotype of CHAT-associated congenital myasthenic syndrome: case series

Congenital myasthenic syndrome with episodic apnea is associated with pathogenic variants in the CHAT gene. While respiratory disorders and oculomotor findings are commonly reported in affected individuals, a subset of patients only present with muscle weakness and/or ptosis but not apneic crises. In this case series, we describe five individuals with exercise intolerance caused by single nucleotide variants in the CHAT gene. The age of onset ranged from 1 to 2.5 years, and all patients exhibited a fluctuating course of congenital myasthenic syndrome without disease progression over several years. Notably, these patients maintained a normal neurological status, except for the presence of abnormal fatigability in their leg muscles following prolonged physical activity. We conducted a modified protocol of repetitive nerve stimulation on the peroneal nerve, revealing an increased decrement in amplitude and area of compound muscle action potentials of the tibialis anterior muscle after 15-20 min of exercise. Treatment with 3,4-diaminopyridine showed clear improvement in two children, while one patient experienced severe adverse effects and is currently receiving a combination of Salbutamol Syrup and pyridostigmine with slight positive effects. Based on our findings and previous cases of early childhood onset with muscle fatigability as the sole manifestation, we propose the existence of a mild phenotype characterized by the absence of apneic episodes.

Vocal Cord Paralysis and Feeding Difficulties as Early Diagnostic Clues of Congenital Myasthenic Syndrome with Neonatal Onset: A Case Report and Review of Literature

Herein, we present a newborn female with congenital vocal cord paralysis who required a tracheostomy in the neonatal period. She also presented with feeding difficulties. She was later diagnosed with a clinical picture of congenital myasthenia, associated with three variants of the MUSK gene: the 27-month follow-up was described. In particular, the c.565C>T variant is novel and has never been described in the literature; it causes the insertion of a premature stop codon (p.Arg189Ter) likely leading to a consequent formation of a truncated nonfunctioning protein. We also systematically collected and summarized information on patients' characteristics of previous cases of congenital myasthenia with neonatal onset reported in the literature to date, and we compared them to our case. The literature reported 155 neonatal cases before our case, from 1980 to March 2022. Of 156 neonates with CMS, nine (5.8%) had vocal cord paralysis, whereas 111 (71.2%) had feeding difficulties. Ocular features were evident in 99 infants (63.5%), whereas facial-bulbar symptoms were found in 115 infants (73.7%). In one hundred sixteen infants (74.4%), limbs were involved. Respiratory problems were displayed by 97 infants (62.2%). The combination of congenital stridor, particularly in the presence of an apparently idiopathic bilateral vocal cord paralysis, and poor coordination between sucking and swallowing may indicate an underlying congenital myasthenic syndrome (CMS). Therefore, we suggest testing infants with vocal cord paralysis and feeding difficulties for MUSK and related genes to avoid a late diagnosis of CMS and improve outcomes.

Clinical and Pathologic Features of Congenital Myasthenic Syndromes Caused by 35 Genes-A Comprehensive Review

Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders characterized by impaired neuromuscular signal transmission due to germline pathogenic variants in genes expressed at the neuromuscular junction (NMJ). A total of 35 genes have been reported in CMS (AGRN, ALG14, ALG2, CHAT, CHD8, CHRNA1, CHRNB1, CHRND, CHRNE, CHRNG, COL13A1, COLQ, DOK7, DPAGT1, GFPT1, GMPPB, LAMA5, LAMB2, LRP4, MUSK, MYO9A, PLEC, PREPL, PURA, RAPSN, RPH3A, SCN4A, SLC18A3, SLC25A1, SLC5A7, SNAP25, SYT2, TOR1AIP1, UNC13A, VAMP1). The 35 genes can be classified into 14 groups according to the pathomechanical, clinical, and therapeutic features of CMS patients. Measurement of compound muscle action potentials elicited by repetitive nerve stimulation is required to diagnose CMS. Clinical and electrophysiological features are not sufficient to identify a defective molecule, and genetic studies are always required for accurate diagnosis. From a pharmacological point of view, cholinesterase inhibitors are effective in most groups of CMS, but are contraindicated in some groups of CMS. Similarly, ephedrine, salbutamol (albuterol), amifampridine are effective in most but not all groups of CMS. This review extensively covers pathomechanical and clinical features of CMS by citing 442 relevant articles.

Infant Botulism: Checklist for Timely Clinical Diagnosis and New Possible Risk Factors Originated from a Case Report and Literature Review

Infant botulism is a rare and underdiagnosed disease caused by BoNT-producing clostridia that can temporarily colonize the intestinal lumen of infants less than one year of age. The diagnosis may be challenging because of its rareness, especially in patients showing atypical presentations or concomitant coinfections. In this paper, we report the first infant botulism case associated with Cytomegalovirus coinfection and transient hypogammaglobulinemia and discuss the meaning of these associations in terms of risk factors. Intending to help physicians perform the diagnosis, we also propose a practical clinical and diagnostic criteria checklist based on the revision of the literature.

Utility and practice of electrodiagnostic testing in the pediatric population: An AANEM consensus statement

Nerve conduction studies and needle electromyography, collectively known as electrodiagnostic (EDX) studies, have been available for pediatric patients for decades, but the accessibility of this diagnostic modality and the approach to testing vary significantly depending on the physician and institution. The maturation of molecular diagnostic approaches and other diagnostic technologies such as neuromuscular ultrasound indicate that an analysis of current needs and practices for EDX studies in the pediatric population is warranted. The American Association of Neuromuscular & Electrodiagnostic Medicine convened a consensus panel to perform literature searches, share collective experiences, and develop a consensus statement. The panel found that electrodiagnostic studies continue to have high utility for the diagnosis of numerous childhood neuromuscular disorders, and that standardized approaches along with the use of high-quality reference values are important to maximize the diagnostic yield of these tests in infants, children, and adolescents.

Compound Heterozygous CHAT Gene Mutations of a Large Deletion and a Missense Variant in a Chinese Patient With Severe Congenital Myasthenic Syndrome With Episodic Apnea

Congenital myasthenic syndromes (CMSs) are a group of inherited disorders caused by genetic defects in neuromuscular junctions. Mutations in CHAT, encoding choline acetyltransferase, cause congenital myasthenic syndrome with episodic apnea (CMS-EA), a rare autosomal recessive disease characterized by respiratory insufficiency with cyanosis and apnea after infections, fever, vomiting, or excitement. To date, no studies have reported deletions comprised of multiple exons. Here, using next generation sequencing, we identified compound heterozygous mutations, namely a large maternally inherited deletion, including exons 4, 5, and 6, and a paternally inherited missense variant (c.914T>C [p.Ile305Thr]) in CHAT in a Chinese patient with a severe phenotype of CMS-EA. Furthermore, the large deletion was also validated by real-time fluorescence quantitative polymerase chain reaction. The patient was a 10-month-old boy, who presented with a weak cry and feeding difficulties soon after birth, ptosis at 4 months old, episodic apnea after fever at 9 months old, and respiratory insufficiency with cyanosis and apnea that required intubation after a respiratory tract infection at 10 months old. Unfortunately, he died in the Pediatric Intensive Care Unit soon after hospitalization. The patient's elder sister had similar clinical manifestations, and she died prior to the age of 2 months old without a diagnosis. Genotype-phenotype correlation analysis revealed that loss-of-function mutations in exons 4-6 of CHAT might cause more severe CMS-EA. To our knowledge, this is the first study to show compound heterozygous CHAT mutations consisting of a large deletion and missense mutation in a patient with CMS-EA.

Mutation of a serine near the catalytic site of the choline acetyltransferase a gene almost completely abolishes motility of the zebrafish embryo

In zebrafish, the gene choline acetyltransferase a (chata) encodes one of the two ChAT orthologs responsible for the synthesis of acetylcholine. Acetylcholine (ACh) is essential for neuromuscular transmission and its impaired synthesis by ChAT can lead to neuromuscular junction disorders such as congenital myasthenic syndromes in humans. We have identified a novel mutation in the chata gene of zebrafish, chata^tk64, in a collection of uncharacterised ENU-induced mutants. This mutant carries a missense mutation in the codon of a highly conserved serine changing it to an arginine (S102R). This serine is conserved among ChATs from zebrafish, rat, mice and chicken to humans. It resides within the catalytic domain and in the vicinity of the active site of the enzyme. However, it has not been reported so far to be required for enzymatic activity. Modelling of the S102R variant change in the ChAT protein crystal structure suggests that the change affects protein structure and has a direct impact on the catalytic domain of the protein which abolishes embryo motility almost completely.