Congenital myasthenic syndrome due to novel GFPT1 variant presenting with head drop and visual impairment: A case report

Abstract

Background

Glutamine-fructose-6-phosphate transaminase 1 (GFPT1) gene variants are a known cause of congenital myasthenic syndrome (CMS), typically presenting with fatigable limb-girdle weakness and characteristic tubular aggregates on muscle biopsy, though recent reports have broadened the clinical spectrum.

Methods

We describe a 5-year-old boy presenting with hypotonia, progressive muscle weakness with head drop, cognitive delay, and visual impairment, found on neuromuscular genetic panel to have a novel homozygous missense variant in GFPT1 (c.1154G>A, p.Arg385Gln).

Results

Further workup revealed white matter abnormalities with atrophy of corpus callosum and cerebellum on neuroimaging, myopathic motor unit potentials on electromyography, and non-specific changes on the left biceps muscle biopsy with absence of tubular aggregates. Stimulated jitter analysis of the right orbicularis oculi muscle showed increased jitter and blocking indicative of neuromuscular junction (NMJ) transmission defect. Trio whole-exome and trio whole-genome sequencing confirmed autosomal recessive GFPT1-related myasthenia.

Discussion

The muscle-eye-brain (MEB) phenotype of our case was like that of alpha-dystroglycanopathy, a glycosylation-related severe congenital muscular dystrophy. The presence of NMJ abnormalities expands the novel GFPT1 variant genotype-phenotype to include central nervous system features and muscle-eye-brain congenital myasthenic syndrome (MEB-CMS). This case study highlights the role of multiple specialists (neurologist, radiologist, ophthalmologist, pathologist, geneticist) and neurodiagnostic techniques (neuroimaging, electrodiagnostic, muscle pathology) to help deep phenotype symptomatic patients with novel gene variants found on next-generation sequencing.

Keywords

congenital myasthenic syndrome (CMS)glycosylation muscle-eye-brain neuromuscular junction defect

Introduction

Congenital myasthenic syndromes (CMS) are a group of rare, heterogenous inherited disorders with pathogenic genetic variants leading to impaired protein formation necessary for the stability and function of the neuromuscular junction (NMJ). Impaired NMJ transmission leads to fatigable weakness. Patients typically present in the first two years of life with symptoms including hypotonia, feeding and breathing difficulties, and motor delays.¹ Due to the wide variability in CMS symptoms, it is often underdiagnosed or misdiagnosed as myopathy, developmental delay, or hypotonia. Treatments for CMS patients depend on the location of NMJ defect i.e. pre-synaptic, synaptic, or post-synaptic and include acetylcholinesterase inhibitors (e.g., pyridostigmine, neostigmine), 3,4-diaminopyridine (DAP), salbutamol and ephedrine.^2,3 To date, CMS has been found to be associated with variants in over 40 genes encoding pre- and postsynaptic NMJ proteins.¹ Among them, variants in GFPT1, a gene involved in the glycosylation of NMJ components, are becoming an increasingly recognized cause of autosomal recessive limb-girdle CMS.

GFPT1 encodes for glutamine-fructose-6-phosphate transaminase 1, an enzyme that catalyzes the initial and rate-determining step of the hexosamine biosynthetic pathway regulating the glycosylation of key NMJ proteins including acetylcholine receptor subunits^1,4 (Figure 1). The pathogenic GFPT1 variants result in decreased NMJ acetylcholine receptor expression and impaired signaling. These abnormalities are reflected in the electrophysiologic findings like attenuated responses to repetitive nerve stimulation and increased jitter on single-fiber electromyography.^5,6 The most typical clinical presentation of GFPT1-CMS is fatigable proximal (limb-girdle) muscle weakness, usually accompanied by tubular aggregates on muscle biopsy.^7,8 While this presentation remains the classic phenotype, recent case studies and reports have broadened our understanding of the clinical, pathologic, and genetic spectrum associated with GFPT1-CMS.

Figure 1.

The role of glutamine-fructose-6-phosphate transaminase 1 (GFPT1) in postsynaptic signal transmission. GFPT1 variants result in reduced urine diphosphate-N-acetylglucosamine (UDP-GlcNAc), leading to reduced glycosylation of key NMJ proteins including acetylcholine receptor subunits and ultimately decreased muscle contraction.

Recently published case reports on GFPT1-CMS have included descriptions of patients with other clinical manifestations, including respiratory insufficiency, ptosis, opthalmoparesis, facial weakness, neck weakness, and distal weakness.^4,8–10 Other clinical observations include retinal involvement (e.g., juvenile macular degeneration leading to vision loss), leukoencephalopathy on neuroimaging, and metacarpophalangeal joint hyperextension, raising questions about potential connective tissue involvement or overlapping mechanisms with other congenital muscle disorders such as seen in muscle-eye-brain disease (MEB), a disorder of glycosylation (alpha-dystroglycanopathies).^2,9–11

Pathologically, most GFPT1-CMS patients present with tubular aggregates on muscle biopsy, the extent and distribution of which have been shown to correlate with severity of disease burden.¹ Tubular aggregates are sarcoplasmic reticulum–derived inclusions believed to represent a compensatory response to intracellular calcium dysregulation.¹ However, not all patients demonstrate this classic finding. Several case reports have described alternative or additional pathologic features, including rimmed vacuoles, desmin-positive myofibrillar disorganization, ragged red fibers, and Z-disc disruption, highlighting the heterogeneity of muscle pathology in GFPT1-CMS.^2,4,7,9,10

Of note, the number of GFPT1 variants known to cause CMS is increasing, with case studies continuing to identify novel variants.^4,6,8,10 These findings show that GFPT1-CMS represents a broad and variable disorder with clinical, pathological, and genetic features that continue to evolve with ongoing research (Table 1). We present a novel case of a GFPT1 gene variant confirmed to have CMS using stimulated jitter analysis. This study was approved by the local institution review board (00002814).

Table 1.

Review of literature on GFPT1 congenital myasthenic syndrome.

Author, year	N number	Specific GFPT1 variant(s)	Main takeaways
Guergueltcheva, 2011⁹	24 (from 14 families)	Multiple, unspecified	- First detailed report linking GFPT1 variants to CMS phenotypes and tubular aggregates
			- Neck muscle weakness observed in several patients
			- Retinal involvement reported in some patients
Senderek, 2011¹²	18 (from 13 families)	Multiple	- Identified 18 different biallelic GFPT1 mutations in autosomal recessive CMS
Senderek, 2011¹²	18 (from 13 families)	Multiple	- Reduced GFPT1 expression in zebrafish embryos led to abnormal muscle fiber structure and disrupted neuromuscular junction development, supporting its essential role in NMJ function.
Bauché, 2017¹³	11 (from 9 families)	Multiple	- Long-term follow-up demonstrated that GFPT1-CMS evolved toward a myopathic weakness over time
Bauché, 2017¹³	11 (from 9 families)	Multiple	- Muscle biopsy molecular analysis revealed tubular aggregates and reduced O-glycosylation and sialylation of transmembrane proteins
Helman, 2019²	4 (from 2 families)	c.41G>T, p.R14L; c.452C>A, p.T151K	-Novel GFPT1-CMS variants observed with leukoencephalopathy and ragged red fibers on muscle biopsy, possible link with mitochondrial dysfunction
Helman, 2019²	4 (from 2 families)	c.41G>T, p.R14L; c.452C>A, p.T151K	-Symptom improvement noted with pyridostigmine treatment
Luo, 2019⁶	2 (siblings)	c.462G>C, p.K154N; c.1088A>G, p.N363S	- Novel missense variants identified causing GFPT1-CMS with tubular aggregates
Szelinger, 2020⁸	3 (from 2 families)	c.686dupC, p.R230*	- New frameshift variant discovered with novel maternal UDP inheritance
			- CMS symptoms present congenitally at birth
			- Respiratory insufficiency reported as a new clinical feature
Ma, 2021¹⁰	1	c.T581T>C, p.F194S; c.T14T>A, p.F5Y	- New heterozygous GFPT1 variants linked to CMS
			- Muscle biopsy showed expected tubular aggregates plus novel rimmed vacuoles
			- Muscle weakness also observed around metacarpophalangeal joints
An, 2022¹	3 (unrelated)	c.331C>T, p.R111C; c.44C>T, p.T15M	-Patients showed classic limb-girdle weakness
			-First report of decremental responses to both low and high frequency repetitive nerve stimulation
			-Severity of tubular aggregates on biopsy correlated with severity of disease and serum creatine kinase levels
Huang, 2022⁵	9 (1 GFPT1)	c.331C>T, p.R111C; c.635G>A, p.R212Q	- Reinforced role of GFPT1 point variants in CMS, especially c.331C>T variant
Jiang 2022⁷	2 (unrelated)	c.331C>T, p.R111C; c.332G>A, p.R111H; c.1534C>T, p.R512W	-Demonstrates a case of GFPT1-CMS without tubular aggregates on muscle biopsy; biopsy showed myofibrillar myopathy with desmin buildup, Z-disc disruption, and vacuoles
Polavarapu 2024¹⁴	10	Multiple	- Emphasized the growing importance of glycosylation pathway genes (DPAGT1, GFPT1, and GMPPB) as contributors to NMJ dysfunction
Polavarapu 2024¹⁴	10	Multiple	- Patients with glycosylation-related defects showed favorable responses to dual therapy with pyridostigmine and salbutamol
Zhang, 2025⁴	24	Multiple, including “hotspot” variant c.331C>T, p.R111C and novel variant c.704C>G, p.S235*	-Identified ocular involvement in 6 patients (ptosis, ophthalmoparesis)
			- Defined “hotspot” c.331C>T variant common in Chinese population
			- Homozygous variants associated with more severe phenotypes
			-Further evidence that tubular aggregates are common but not always present in cases of GFPT1-CMS
Camelo-Filho, 2025¹⁵	5 (from 2 families)	c.41G>A	- Further delineated the clinical spectrum of GFPT1-CMS through multimodal neuromuscular evaluation, including nerve conduction studies, electromyography, repetitive nerve stimulation, and muscle ultrasound.
Camelo-Filho, 2025¹⁵	5 (from 2 families)	c.41G>A	- Described a patient with GFPT1-CMS and central nervous system involvement including neonatal onset epilepsy and cognitive impairment
Ramezani, 2026¹⁶	9	Multiple	-Further characterized new GFPT1 variants causing CMS, as well as other glycosylation-related variants
Ramezani, 2026¹⁶	9	Multiple	-Patients with GFPT1-CMS had a median age of onset of 6 but a median age at diagnosis of 24, highlighting the diagnostic challenge and delay in recognition of this condition

Case description

Five-year-old boy with global developmental delay, hypotonia, cognitive delay, and visual impairment presented to the neuromuscular clinics at a tertiary care children’s hospital. He was born full-term to consanguineous parents (first cousins) of Guinean ancestry and spent two weeks in the neonatal intensive care unit for respiratory distress syndrome. His early life was marked with delayed developmental milestones; he rolled at 6-7 months, sat at 12 months, cruised at 2.5 years, and continues to be non-ambulatory. On neurological examination he was non-verbal with poor visual fixation or tracking. He had diffuse hypotonia with muscle weakness, intact tendon jerks and significant head drop (Supplemental Figure 1). Ophthalmic examination demonstrated light perception vision in both eyes, with severely reduced visual function and large excavated macular lesions surrounded by hyperpigmented rims bilaterally. The optic nerve heads appeared normal in both eyes. Macular optical coherence tomography showed prominent outer band loss. He required assistance with activities of daily living including feeding, dressing, and toileting. His medical history was significant for sickle cell trait and possible alpha thalassemia. There is no family history of neuromuscular disease, but he has a full sibling with an unrelated Lipodystrophy condition.

Patient underwent neuromuscular genetic panel testing and was found to have a homozygous missense variant in GFPT1 (NM_001244710.1) c.1154G>A (p.Arg385Gln) (GRCh37/hg 19 chr2-69569333-C-T). This is a missense variant resulting in a single amino acid substitution of arginine for glutamine. This precise variant is novel and has not previously been reported in an individual with this disorder, but a different missense variant at this position has been previously reported in an individual with this condition (PubMed identification: 40442802) (PM5 supporting).⁴ It is present rarely in population databases (1/1611910 gnomAD v4.1) (PM2-supporting). This variant localizes to the SIS1 functional domain, in which other pathogenic variants have been described (PM1-supporting). This variant’s rare exome variant ensemble learner (REVEL) score (0.521) does not provide supportive evidence for pathogenicity, but other prediction tools do support an impact on protein structure/function [Protein variation effect analyzer (PROVEAN) -3.86, Alpha Missense 0.8021, deleterious annotation of genetic variants using neural networks (DANN) 0.9995] (PP3-moderate). This variant raised suspicion for a possible CMS, though his precise diagnosis remained uncertain due to the novelty of this variant and his nonspecific symptoms.

To further investigate his clinical features and genetic findings, we performed an electromyography with concentric needle electrode of the right biceps brachii and tibialis anterior muscles. The insertion and spontaneous activity of the muscles were normal; however, the motor unit potentials were small, short duration, polyphasic with early recruitment indicating chronic non-irritable myopathy such as seen in congenital myopathy. A brain magnetic resonance imaging without contrast showed abnormal signal within the posterior periventricular white matter with associated volume loss of the posterior corpus callosum, as well as a small cerebellar vermis with prominent interfolia spaces suggestive of congenital hypoplasia with or without superimposed volume loss, and small bilateral incompletely rotated hippocampi (Supplemental Figure 2). Left biceps muscle biopsy was performed, showing scattered mildly atrophic myofibers and several with multiple internalized nuclei and some fragmentation of the internal myofibrillar architecture (Supplemental Figure 3). Of note, no tubular aggregates were present on biopsy.

To study the NMJ transmission, the stimulated jitter analysis (stim-JA) of the right orbicularis oculi muscle was performed. Twenty apparent single fiber action potentials (ASFAPs) were recorded with mean jitter value of 69 µs (normal < 24 µs). 95% of ASFAPs (n=19) showed increased jitter and 55% (n=8) were blocked. The NMJ transmission defect on stim-JA study confirmed the clinical and genetic suspicions of CMS. The patient was given a trial of oral pyridostigmine but showed no clinical improvement.

GFPT1 variant was affirmed on his trio exome and trio genome sequencing, in addition to sickle cell trait. No other candidate variants were identified on trio exome, trio genome, or mitochondrial genome sequencing. As other possible Congenital Myasthenic Syndrome genes were covered on this testing, in combination with other clinical and neurophysiological features, our patient’s phenotype is highly specific for GFPT1 congenital disorder of glycosylation (PP4-moderate). His parents are heterozygous for the GFPT1 variant. We classify this variant as likely pathogenic for our patient’s history according to the American College of Medical Genetics and Genomics standards and guidelines for the interpretation of sequence variants (PMID: 25741868).

Conclusions

The index case underscores the importance of deep phenotyping a genotype based on suspected clinical presentation. The homozygous GFPT1 variant identified in our study patient (c.1154G>A p.Arg385Gln) has not, to our knowledge, been previously reported in individuals with CMS. While the routine electrodiagnostic testing and muscle biopsy indicated myopathy, the findings were nonspecific and inconclusive. The stim-JA study confirmed NMJ dysfunction, highlighting the importance of neurophysiological studies in neuromuscular disorder patients in novel gene variants.

Congenital myasthenic syndromes can present broadly and can be diagnostically challenging due to their clinical overlap with other neuromuscular disorders.¹⁰ This report contributes to the growing body of evidence illustrating the genetic and phenotypic heterogeneity of GFPT1-CMS and underscores the importance of recognizing atypical presentations. We reviewed the published English literature describing GFPT1-CMS cases from the past 15 years and have summarized key findings in Table 1.

Our study patient demonstrates an atypical presentation of GFPT1-CMS, with features of cognitive delay and visual impairment that extend beyond the classic neuromuscular phenotype. Although central nervous system (CNS) involvement is uncommon, it has been reported among GFPT1-CMS patients, including a case described by Camelo-Filho et al. (2025) with neonatal-onset epilepsy and cognitive impairment.¹⁵ Visual manifestations have also been documented, as Guergueltcheva et al. (2011) reported GFPT1-CMS patients with macular degeneration and retinitis pigmentosa.⁹ In this context, our case further supports the presence of CNS involvement in GFPT1-CMS and expands the recognized clinical spectrum to include both cognitive and visual manifestations.

GFPT1 pathogenic variants lead to abnormal glycosylation of key neuromuscular junction proteins. Of note, variants in several other genes including DPAGT1, ALG2, ALG14, and GMPPB have been reported to cause CMS through similar disruptions in glycosylation of NMJ proteins.^16–21 The glycosylation defects lead to central nervous system abnormalities such as cerebral and cerebellar atrophy, white matter abnormalities including corpus callosum defects, and brain malformations including cysts, visual impairment and retinal abnormalities. Together these findings are referred to as muscle-eye-brain (MEB) disease. Recent case reports describe overlapping features among patients with variants in the above-mentioned genes and severe truncal hypotonia.^3,17–19 Interestingly, DPAGT1 has also been linked with intellectual disability in a set of siblings with CMS, while ALG14-CMS was associated with delayed myelination, cerebral atrophy, and hypotonia in another sibling pair.^20,21 It has even been shown that significant phenotypic variability can occur among family members carrying identical glycosylation-related CMS variants, underscoring the complexity of genotype–phenotype correlations.¹⁶ Our patient’s case adds to this growing evidence of multi-system involvement that broadens the recognized disease spectrum of glycosylation-related CMS and underscores the need to systemically evaluate CNS involvement in affected patients.

Our patient’s muscle biopsy lacked the tubular aggregates that are typically considered pathognomonic for GFPT1-CMS. Instead, histopathology revealed scattered atrophic myofibers with internalized nuclei and disrupted myofibrillar architecture. Although rare, similar biopsy findings have been described in other cases of GFPT1-CMS, highlighting the broader pathological spectrum than previously appreciated.^4,7,9,10 CMS with nonspecific biopsy changes, lacking tubular aggregates, has additionally been described for glycosylation-related ALG2 and ALG14 variants.¹⁷

Limitations of this case include lack of animal models of this novel GFPT1 variant. We were unable to obtain alpha dystroglycan staining on the muscle. Nevertheless, the case illustrates the challenges in diagnosis of CMS and the utility of stimulated jitter analysis to deep phenotype novel gene variants in a setting of unexplained muscle weakness.

This case expands the clinical, pathological, neurophysiological and genetic understanding of GFPT1-CMS and emphasizes the importance of deep phenotyping a novel genotype. This case highlights the expanding spectrum of glycosylation-related CMS, CNS involvement, and overlapping features of the muscle-eye-brain phenotype.

Supplemental material

Supplemental material - Congenital myasthenic syndrome due to novel GFPT1 variant presenting with head drop and visual impairment: A case report

Supplemental material for Congenital myasthenic syndrome due to novel GFPT1 variant presenting with head drop and visual impairment: A case report by Katharine Torrey, Rachel Logan, Emmanuelle Tiongson, John V. Dennison, Andrew Fischer, Nieraj Jain, Matthew Schniederjan, Ricardo A. Maselli, Sumit Verma in Journal of Neuromuscular Diseases

Footnotes

Acknowledgements

We are grateful to our patient and his family for their trust and for allowing us to write up this case. We also extend our gratitude to the multidisciplinary care team for their expertise and collaboration.

ORCID iDs

Katharine Torrey

Andrew Fischer

Ethical considerations

We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines.

Consent to participate

The patient’s guardian provided written informed consent for participation in this case report and any accompanying images. Every effort has been made to protect patient identity.

Consent for publication

The patient’s guardian provided written informed consent for publication of this case report and any accompanying images.

Author Contributions

Katharine Torrey, BA, and Sumit Verma, MD conceived the study. Katharine Torrey, BA, Rachel Logan, CGC, Emmanuelle Tiongson, MD, Andrew Fischer, MD, Nieraj Jain, MD, Matthew Schniederjan, MD, John V. Dennison, MD, Sumit Verma, MD, collected data and reviewed and revised the manuscript. Ricardo A. Maselli, MD, reviewed the manuscript. Katharine Torrey, BA, and Sumit Verma, MD, drafted a significant portion of the manuscript, conceptualized, coordinated, and supervised data collection, and critically reviewed the manuscript for important intellectual content. Rachel Logan, CGC, reviewed and revised portions of the manuscript and provided variation annotation details. All authors approved the final manuscript as submitted and agreed to be accountable for all aspects of the work.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Supplemental material

Supplemental material for this article is available online.

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