Leukoencephalopathy due to variants in GFPT1-associated congenital myasthenic syndrome

Agenesis of Pectoralis Major Muscle in Late-Onset GFPT1-Related Congenital Myasthenic Syndrome: A Case Report

Objectives

The objective of this study was to expand the phenotypic spectrum of glutamine-fructose-6-phosphate transaminase 1 (GFPT1)-related congenital myasthenia syndrome (CMS).

Methods

A 61-year-old man with agenesis of the left pectoralis major muscle presented with progressive muscle weakness for a decade that transiently improved after exertion.

Results

His examination revealed proximal and distal muscle weakness in upper extremities and proximal muscle weakness in lower extremities. Muscle enzymes were elevated. An electromyogram revealed a myopathic pattern; however, a muscle biopsy of deltoid muscle and genetic testing for limb-girdle muscular dystrophies were nondiagnostic. A 3-Hz repetitive nerve stimulation of the spinal accessory nerve recording from trapezius muscle demonstrated a >20% drop in amplitude of the 5th compound motor action potential relative to 1st at both baseline and after 45-second exercise. Acetylcholine receptor binding, lipoprotein-related protein 4, muscle-specific kinase, and voltage-gated calcium channel P/Q antibodies were negative. Genetic testing targeting CMS revealed 2 likely pathogenic variants within GFPT1: novel c.7+2T>G (intron 1) that was predicted to result in a null allele and known c*22 C>A (exon 19) associated with reduced GFPT1 expression. His muscle strength dramatically improved after pyridostigmine initiation.

Discussion

In addition to other reported neurodevelopmental abnormalities, pectoralis major muscle agenesis (or Poland syndrome) may be a clinical manifestation of GFPT1-related CMS.

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.

Identification of Novel Genetic Markers for the Risk of Spinal Pathologies: A Genome-Wide Association Study of 2 Biobanks

BACKGROUND

Identifying genetic risk factors for spinal disorders may lead to knowledge regarding underlying molecular mechanisms and the development of new treatments.

METHODS

Cases of lumbar spondylolisthesis, spinal stenosis, degenerative disc disease, and pseudarthrosis after spinal fusion were identified from the UK Biobank. Controls were patients without the diagnosis. Whole-genome regressions were used to test for genetic variants potentially implicated in the occurrence of each phenotype. External validation was performed in FinnGen.

RESULTS

A total of 389,413 participants were identified from the UK Biobank. A locus on chromosome 2 spanning GFPT1, NFU1, AAK1, and LOC124906020 was implicated in lumbar spondylolisthesis. Two loci on chromosomes 2 and 12 spanning genes GFPT1, NFU1, and PDE3A were implicated in spinal stenosis. Three loci on chromosomes 6, 10, and 15 spanning genes CHST3, LOC102723493, and SMAD3 were implicated in degenerative disc disease. Finally, 2 novel loci on chromosomes 5 and 9, with the latter corresponding to the LOC105376270 gene, were implicated in pseudarthrosis. Some of these variants associated with spinal stenosis and degenerative disc disease were also replicated in FinnGen.

CONCLUSIONS

This study revealed nucleotide variations in select genetic loci that were potentially implicated in 4 different spinal pathologies, providing potential insights into the pathological mechanisms.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Abnormal decrement on high-frequency repetitive nerve stimulation in congenital myasthenic syndrome with GFPT1 mutations and review of literature

Objectives

Congenital myasthenic syndrome (CMS) is a clinically and genetically heterogeneous group of inherited disorders characterized by neuromuscular junction defects. Mutations in GFPT1 have been shown to underlie CMS. An increasing number of patients with CMS due to mutations in GFPT1 have been reported. However, a comprehensive review of clinical and genetic analyses of GFPT-related CMS worldwide is lacking, especially, given that the common or hotspot mutations in GFPT1 have not been reported. Here, we described the clinical and genetic findings of three patients with GFPT1 mutations from southwestern China and reviewed the clinical and genetic features of patients with GFPT1-related CMS worldwide.

Methods

Clinical, laboratory, electrophysiological, myopathological, and genetic analyses of three patients with GFPT1-related CMS from southwestern China were conducted, and a review of previously published or reported cases about congenital myasthenic syndrome with GFPT1 mutations in the PubMed database was made.

Results

The clinical, laboratory, electrophysiological, and myopathological features by muscle biopsy of three patients with GFPT1-related CMS were consistent with those of previously reported patients with GFPT1 mutations. Additionally, an abnormal decrement in high-frequency RNS was found. Two different homozygous missense mutations (c.331C>T, p.R111C; c.44C>T, p.T15M) were detected by whole-exome sequencing (WES) or targeted neuromuscular disorder gene panels.

Conclusion

A distinct decremental response to high-frequency RNS was found in three patients with GFPT1-related CMS from southwestern China, which has never been reported thus far. In addition, the location and degree of tubular aggregates (TAs) seemed to be associated with the severity of clinical symptoms and serum creatine kinase levels, further expanding the phenotypic spectrum of GFPT1-related CMS. Lastly, some potential hotspot mutations in GFPT1 have been found in GFPT1-CMS worldwide.

GFPT1-Associated Congenital Myasthenic Syndrome Mimicking a Glycogen Storage Disease – Diagnostic Pitfalls in Myopathology Solved by Next-Generation-Sequencing

GFPT1-related congenital myasthenic syndrome (CMS) is characterized by progressive limb girdle weakness, and less prominent involvement of facial, bulbar, or respiratory muscles. While tubular aggregates in muscle biopsy are considered highly indicative in GFPT1-associated CMS, excessive glycogen storage has not been described. Here, we report on three affected siblings with limb-girdle myasthenia due to biallelic pathogenic variants in GFPT1: the previously reported missense variant c.41G >  A (p.Arg14Gln) and the novel truncating variant c.1265_1268del (p.Phe422TrpfsTer26). Patients showed progressive proximal atrophic muscular weakness with respiratory involvement, and a lethal disease course in adulthood. In the diagnostic workup at that time, muscle biopsy suggested a glycogen storage disease. Initially, Pompe disease was suspected. However, enzymatic activity of acid alpha-glucosidase was normal, and gene panel analysis including 38 genes associated with limb-girdle weakness (GAA included) remained unevocative. Hence, a non-specified glycogen storage myopathy was diagnosed. A decade later, the diagnosis of GFPT1-related CMS was established by genome sequencing. Myopathological reexamination showed pronounced glycogen accumulations, that were exclusively found in denervated muscle fibers. Only single fibers showed very small tubular aggregates, identified in evaluation of serial sections. This family demonstrates how diagnostic pitfalls can be addressed by an integrative approach including broad genetic analysis and re-evaluation of clinical as well as myopathological findings.

Deduction and exploration of the evolution and function of vertebrate GFPT family

BACKGROUND

Glutamine-fructose-6-phosphate aminotransferase (GFPT) is a key factor in the hexosamine metabolism pathway. It regulates the downstream factor O-GlcNAc to change cell function and plays an important role in the metabolism and immune process of tissues and organs. However, the evolutionary relationship of GFPT family proteins in vertebrates has not been elucidated.

OBJECTIVE

To deduce and explore the evolution and function of vertebrate GFPT family.

METHODS

18 GFPT sequences were obtained from Homo sapiens (H. sapiens), Trachypithecus francoisi (T. francoisi), Mus musculus (M. musculus), Rattus norvegicus (R. norvegicus), Gallus gallus (G. gallus), Zootoca vivipara (Z. vivipara), Xenopus tropicalis (X. tropicalis), Danio rerio (D. rerio), Rhincodon typus (R. typus), Plasmodium relictum from National Center for Biotechnology Information (NCBI). The physical and chemical characteristics and molecular evolution of GFPT family proteins and nucleic acid sequences were analyzed by ClustalX2, Gene Doc, MEGA-X, SMART, Datamonkey, R etc. RESULTS: Based on the neighbor-joining (NJ) phylogenetic tree and evolution fingerprints, GFPT family members of vertebrates can be divided into two groups: the GFPT1 group and the GFPT2 group. Seven positive selection sites were identified by IFEL and integrated methods mixed effects model of evolution (MEME) and fixed effects likelihood (REL). Finally, we predicted 28 phosphorylation sites and 18 ubiquitousness sites in the human GFPT1 sequence, 10 phosphorylation sites, and five ubiquitousness sites in GFPT2. Gene ontology (GO) analyzes the protein molecules and KEGG signaling pathways of vertebrates interacting with GFPT family proteins.

CONCLUSIONS

Our work confirmed that higher animals GFPT family may have differentiated GFPT1 and GFPT2, which meets their own functional needs. This knowledge answers the question what the origin and evolution of GFPT family in vertebrates and provided the basis for disease treatment and function research of GFPT protein.

Diverse myopathological features in the congenital myasthenia syndrome with GFPT1 mutation

INTRODUCTION

Mutations in the GFPT1 gene are associated with a particular subtype of congenital myasthenia syndrome (CMS) called limb-girdle myasthenia with tubular aggregates. However, not all patients show tubular aggregates in muscle biopsy, suggesting the diversity of myopathology should be further investigated.

METHODS

In this study, we reported two unrelated patients clinically characterized by easy fatigability, limb-girdle muscle weakness, positive decrements of repetitive stimulation, and response to pyridostigmine. The routine examinations of myopathology were conducted. The causative gene was explored by whole-exome screening. In addition, we summarized all GFPT1-related CMS patients with muscle biopsy in the literature.

RESULTS

Pathogenic biallelic GFPT1 mutations were identified in the two patients. In patient one, muscle biopsy indicated vacuolar myopathic changes and atypical pathological changes of myofibrillar myopathy characterized by desmin deposits, Z-disc disorganization, and electronic dense granulofilamentous aggregation. In patient two, muscle biopsy showed typical myopathy with tubular aggregates. Among the 51 reported GFPT1-related CMS patients with muscle biopsy, most of them showed tubular aggregates myopathy, while rimmed vacuolar myopathy, autophagic vacuolar myopathy, mitochondria-like myopathy, neurogenic myopathy, and unspecific myopathic changes were also observed in some patients. These extra-synaptic pathological changes might be associated with GFPT1-deficiency hypoglycosylation and altered function of muscle-specific glycoproteins, as well as partly responsible for the permanent muscle weakness and resistance to acetylcholinesterase inhibitor therapy.

CONCLUSIONS

Most patients with GFPT1-related CMS had tubular aggregates in the muscle biopsy, but some patients could show great diversities of the pathological change. The myopathological findings might be a biomarker to predict the prognosis of the disease.

Congenital myasthenic syndrome in a cohort of patients with 'double' seronegative myasthenia gravis

BACKGROUND

Congenital myasthenic syndromes (CMS) have some phenotypic overlap with seronegative myasthenia gravis (SNMG).

OBJECTIVE

The aim of this single center study was to assess the minimum occurrence of CMS misdiagnosed as double SNMG in a Brazilian cohort.

METHODS

The genetic analysis of the most common mutations in CHRNE, RAPSN, and DOK7 genes was used as the main screening tool.

RESULTS

We performed genetic analysis in 22 patients with a previous diagnosis of 'double' SNMG. In this study, one CMS patient was confirmed due to the presence of compound heterozygous variants in the CHRNE gene (c.130insG/p.Cys210Phe).

CONCLUSIONS

This study confirmed that CMS due to CHNRE mutations can be mistaken for SNMG. In addition, our study estimated the prevalence of misdiagnosed CMS to be 4.5% in 'double' SNMG patients of our center. Based on our findings, genetic screening could be helpful in the diagnostic workup of patients with 'double' SNMG in whom differential diagnosis is recommended.

Comprehensive Transcriptomic Profiling of Murine Osteoclast Differentiation Reveals Novel Differentially Expressed Genes and LncRNAs

Osteoclasts are the sole bone resorbing cells, which undertake opposing roles to osteoblasts to affect skeletal mass and structure. However, unraveling the comprehensive molecular mechanisms behind osteoclast differentiation is necessitated to overcome limitations and scarcity of available data, particularly in relation with the emerging roles of long non-coding RNAs (LncRNAs) in gene expression. In this study, we performed comprehensive and progressive analyses of the dynamic transcriptomes of murine osteoclasts, generated in vitro. We compared the total RNA-based transcriptomes of murine bone marrow derived cells with differentiated osteoclasts, while focusing on potentially novel genes and LncRNAs, to uncover critical genes and their associated pathways, which are differentially regulated during osteoclast differentiation. We found 4,214 differentially regulated genes during osteoclast differentiation, which included various types of LncRNAs. Among the upregulated protein coding genes not previously associated with osteoclast are Pheta1, Hagh, Gfpt1 and Nol4, while downregulated genes included Plau, Ltf, Sell and Zfp831. Notably, we report Nol4 as a novel gene related to osteoclast activity since Nol4 knockout mice Nol4^{em1(International Mouse Phenotyping Consortium)J} exhibit increased bone mineral density. Moreover, the differentially expressed LncRNAs included antisense and long intergenic non-coding RNAs, among others. Overall, immune-related and metabolism-related genes were downregulated, while anatomical morphogenesis and remodeling-related genes were upregulated in early-differentiated osteoclasts with sustained downregulation of immune-related genes in mature osteoclasts. The gene signatures and the comprehensive transcriptome of osteoclast differentiation provided herein can serve as an invaluable resource for deciphering gene dysregulation in osteoclast-related pathologic conditions.

Congenital myasthenic syndrome caused by a frameshift insertion mutation in GFPT1

Objective

Description of a new variant of the glutamine-fructose-6-phosphate transaminase 1 (GFPT1) gene causing congenital myasthenic syndrome (CMS) in 3 children from 2 unrelated families.

Methods

Muscle biopsies, EMG, and whole-exome sequencing were performed.

Results

All 3 patients presented with congenital hypotonia, muscle weakness, respiratory insufficiency, head lag, areflexia, and gastrointestinal dysfunction. Genetic analysis identified a homozygous frameshift insertion in the GFPT1 gene (NM_001244710.1: c.686dupC; p.Arg230Ter) that was shared by all 3 patients. In one of the patients, inheritance of the variant was through uniparental disomy (UPD) with maternal origin. Repetitive nerve stimulation and single-fiber EMG was consistent with the clinical diagnosis of CMS with a postjunctional defect. Ultrastructural evaluation of the muscle biopsy from one of the patients showed extremely attenuated postsynaptic folds at neuromuscular junctions and extensive autophagic vacuolar pathology.

Conclusions

These results expand on the spectrum of known loss-of-function GFPT1 mutations in CMS12 and in one family demonstrate a novel mode of inheritance due to UPD.

[Advances in the diagnosis and treatment of congenital myasthenic syndrome]

Congenital myasthenic syndrome (CMS) is a group of clinical and genetic heterogeneous diseases caused by impaired neuromuscular transmission due to genetic defects. At present, it has been reported that more than 30 genes can cause CMS. All CMS subtypes have the clinical features of fatigue and muscle weakness, but age of onset, symptoms, and treatment response vary with the molecular mechanisms underlying genetic defects. Pharmacotherapy and symptomatic/supportive treatment are the main methods for the treatment of CMS, and antisense oligonucleotide technology has been proven to be beneficial for CHRNA 1-related CMS in animals. Since CMS is a group of increasingly recognized clinical and genetic heterogeneous diseases, an understanding of the latest knowledge and research advances in its clinical features, genetic research, and treatment helps to give early diagnosis and treatment as well as gain a deeper understanding of the pathogenesis of CMS, so as to make new breakthroughs in the treatment of CMS.

Trouble at the junction: When myopathy and myasthenia overlap

Although myopathies and neuromuscular junction disorders are typically distinct, their coexistence has been reported in several inherited and acquired conditions. Affected individuals have variable clinical phenotypes but typically display both a decrement on repetitive nerve stimulation and myopathic findings on muscle biopsy. Inherited causes include myopathies related to mutations in BIN1, DES, DNM2, GMPPB, MTM1, or PLEC and congenital myasthenic syndromes due to mutations in ALG2, ALG14, COL13A1, DOK7, DPAGT1, or GFPT1. Additionally, a decrement due to muscle fiber inexcitability is observed in certain myotonic disorders. The identification of a defect of neuromuscular transmission in an inherited myopathy may assist in establishing a molecular diagnosis and in selecting patients who would benefit from pharmacological correction of this defect. Acquired cases meanwhile stem from the co-occurrence of myasthenia gravis or Lambert-Eaton myasthenic syndrome with an immune-mediated myopathy, which may be due to paraneoplastic disorders or exposure to immune checkpoint inhibitors.