Giant Axonal Neuropathy Research Articles (Page 1)

Neurodegenerative disorders are typically caused by harmful protein accumulation and nerve cell damage. A post-translational modification called O-linked N-acetylglucosamine ylation acts as a critical regulator in these disorders by controlling protein behavior, cell signaling, and energy balance. This modification is dynamically balanced through the cooperative actions of O-linked N-acetylglucosamine transferase and O-GlcNAcase. In healthy brains, O-GlcNAcylation supports nerve cell function and survival, but its imbalance contributes to disease progression. Notably, the effects of O-GlcNAcylation differ across disorders. This review reveals how O-GlcNAcylation bridges molecular mechanisms to neurodegeneration, as well as the prospects of targeted O-linked N-acetylglucosamine acylation therapy for neurodegenerative diseases. In Alzheimer's disease, it blocks toxic changes in key proteins like tau and amyloid-beta. In Parkinson's disease, it reduces the clumping of alpha-synuclein, yet may disrupt dopamine production. In amyotrophic lateral sclerosis, it protects nerve fiber transport systems. Additionally, O-GlcNAcylation plays an indispensable part in other neurodegenerative conditions, including Huntington's disease, aging, Machado-Joseph disease, multiple sclerosis, and giant axonal neuropathy. New therapies targeting this mechanism include glucosamine supplements and O-GlcNAcase inhibitors, which show clinical promise but face translational challenges.

The Kelch 3 motif on gigaxonin mediates the interaction with NUDCD3 and regulates vimentin filament morphology.

Abstract Background Giant axonal neuropathy (GAN) is a rare inherited neurodegenerative disease that affects the peripheral and central nervous systems. Herein, we describe three Egyptian siblings with GAN who showed differences in clinical severity. Case Presentation. Case 1 had slowly progressive sensorimotor polyneuropathy starting from 6 years of age with lack of remarkable central nervous system (CNS) involvement till age of 14 years. In contrast, case 2 showed early-onset neurodevelopmental delay, rapidly progressive course, and significant CNS manifestations. Case 3 had an intermediate phenotype. The extent of brain imaging abnormalities paralleled the clinical severity as case 1 had only moderate white matter changes while case 2 showed extensive white matter lesions, ventriculomegaly, and atrophic changes. Whole-exome sequencing revealed a novel homozygous nonsense GAN variant c.918G > A (p.Trp306Ter). Conclusion This is the first case report of GAN from Egyptian populations, which expands the spectrum of disease-causing variants in the GAN gene and underscores the clinical heterogeneity of this disease even among patients sharing the same genotype and environmental conditions.

Gigaxonin is an intermediate filament (IF)-interacting partner belonging to the Kelch-like (KLHL) protein family. Gigaxonin is encoded by the KLHL16 gene, which is mutated in Giant Axonal Neuropathy (GAN). The lack of functional gigaxonin in GAN patient cells impairs IF proteostasis, leading to focal abnormal accumulations of IFs and compromised neuronal function. We hypothesized that gigaxonin forms molecular interactions via specific sequence motifs to regulate IF proteostasis. The goal of this study was to examine how distinct Kelch motifs on gigaxonin regulate IF protein degradation and filament morphology. We analyzed vimentin IFs in HEK293 cells overexpressing wild type (WT) gigaxonin, or gigaxonin lacking each of the six individual Kelch motifs: K1 (aa274–326), K2 (aa327–374), K3 (aa376–421), K4 (aa422–468), K5 (aa470–522), and K6 (aa528–574). All six gigaxonin deletion mutants (ΔK1-ΔK6) promoted the degradation of soluble vimentin. The ΔK3 gigaxonin mutant exhibited soluble vimentin degradation and promoted the bundling of vimentin IFs relative to WT gigaxonin. Using mass spectrometry proteomic analysis we found that, relative to WT gigaxonin, ΔK3 gigaxonin had increased associations with ubiquitination-associated and mitochondrial proteins and lost the association with the NudC domain-containing protein 3 (NUDCD3), a molecular chaperone enriched in the nervous system. Collectively, our cell biological data show the induction of an abnormal GAN-like IF phenotype in cells expressing ΔK3-gigaxonin, while our mass spectrometry profiling links the loss of gigaxonin-NUDCD3 interactions with defective IF proteostasis, revealing NUDCD3 as a potential new target in GAN.

Neurofilament accumulation is associated with many neurodegenerative diseases, but it is the primary pathology in giant axonal neuropathy (GAN). This childhood-onset autosomal recessive disease is caused by loss-of-function mutations in gigaxonin, the E3 adaptor protein that enables neurofilament degradation. Using a combination of genetic and RNA interference approaches, we found that dorsal root ganglia from mice lacking gigaxonin have impaired autophagy and lysosomal degradation through 2 mechanisms. First, neurofilament accumulations interfere with the distribution of autophagic organelles, impairing their maturation and fusion with lysosomes. Second, the accumulations attract the chaperone 14-3-3, which is responsible for the proper localization of the key autophagy regulator transcription factor EB (TFEB). We propose that this dual disruption of autophagy contributes to the pathogenesis of other neurodegenerative diseases involving neurofilament accumulations.

Abstract Background: Giant axonal neuropathy (GAN) type 1 is a rare autosomal recessive, progressive neuro-degenerative disorder, caused by biallelic variants in Gigaxonin (GAN) gene. Clinical Description: An 11-year-old boy born out of consanguineous marriage presented with features of regression of milestones, initially motor, followed by cognitive and speech abnormality, associated with seizures and hearing impairment progressing over past 2–3 years. On examination, he had kinky hair, nystagmus, with diffuse muscle atrophy, absent tendon reflexes, positive cerebellar signs as well as impairment of higher mental functions. Management and Outcome: Laboratory investigations were largely normal, with magnetic resonance imaging showing features of diffuse white matter abnormality with signal changes noted in the dentate nuclei. Exome sequencing identified a homozygous likely pathogenic stop-gain variant in GAN gene. Parents were counselled and child was provided supportive care. Conclusion: The case creates awareness among pediatricians regarding the rare disorder of GAN. A thorough neurological assessment with careful physical examination along with a knowledge of this disorder will help in making an early diagnosis.

BackgroundGiant axonal neuropathy 1 (GAN) is a rare neurodegenerative disorder with autosomal recessive inheritance and significant phenotypic heterogeneity, ranging from milder presentations resembling Charcot–Marie–Tooth disease (CMT) to classical presentations involving central and peripheral nervous systems. We investigated the genetic and clinical spectrum of GAN in Japanese patients with inherited peripheral neuropathies (IPNs).MethodsWe conducted genetic screening of 3315 Japanese patients diagnosed with IPNs between 2007 and 2023 using targeted next-generation or whole-exome sequencing. Variant pathogenicity, clinical features, and neurophysiological and neuroimaging findings were reviewed.ResultsWe identified seven biallelic GAN variants in five patients from four unrelated families, including one homozygous and three compound heterozygous genotypes. Two novel pathogenic variants were identified: c.922G > T (p.Glu308*) and c.456dup (p.Ala153Cysfs*27). Two families exhibited the classical phenotype, whereas the other two exhibited a CMT-like phenotype. Mean onset age was 4.4 years (range 1.5–8), and gait disturbance was the initial symptom. The most common findings included distal weakness (n = 5), sensory impairment (n = 4), scoliosis (n = 3), autonomic dysfunction (n = 2). Neurophysiologically, all patients had sensorimotor axonal polyneuropathy. One patient with mild phenotype maintained a CMT-like state without systemic involvement until the age of 43 years and was still alive at 72, representing the longest documented survival in GAN.ConclusionThis study expands the genetic and phenotypic spectrum of GAN by identifying novel variants and a long-term survivor. These findings underscore the importance of systematic genetic screening for GAN in pediatric-onset CMT, even in the absence of classical features.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00415-025-13243-5.

Giant axonal neuropathy (GAN) is a progressive neurodegenerative disease affecting the peripheral and central nervous system and is caused by bi-allelic variants in the GAN gene, leading to loss of functional gigaxonin protein. A treatment does not exist, but a first clinical trial using a gene therapy approach has recently been completed. Here, we conducted the first systematic study of GAN patients treated by German-speaking child neurologists. We collected clinical, genetic, and epidemiological data from a total of 15 patients representing one of the largest cohorts described thus far. Average age of patients was 11.7 years at inclusion. The most frequently reported symptoms (HPO coded) were gait disturbance and muscle weakness, abnormality of muscle size, and abnormal reflexes. In line with the frequency of homozygous variants, in five families, parents reported being at least distantly related. In 14 patients, diagnosis was confirmed by molecular genetic testing, revealing eight different GAN variants, four being reported as pathogenic in the literature. Proteomics of white blood cells derived from four patients was conducted to obtain unbiased insights into the underlying pathophysiology and revealed dysregulation of 111 proteins implicated in diverse biological processes. Of note, diverse of these proteins is known to be crucial for proper synaptic function and transmission and affection of intermediate filament organisation and proteolysis, which is in line with the known functions of gigaxonin.

Background& Objective: Giant axonal neuropathy (GAN) is a serious progressive neurodegenerative disease. The aim of this study is to evaluate the frequency and phenotypic-genotypic characteristics of GAN patients, which, like many rare diseases, is disguised under the name of polyneuropathy, and to present our experience. Methods: In this retrospective observational study, 105 pediatric patients with polyneuropathy were screened. Demographic characteristics and clinical diagnoses were reviewed. The mean age of the patients was 10.9 years (2-18), 59 were boys (56%) and 46 were girls (44%). GAN patients who were genetically diagnosed by single gene analysis were clinically evaluated in detail. Results: Regarding the etiology of polyneuropathy, 43% of patients had acquired and 57% had hereditary causes. Among hereditary cases, 29% had an unknown diagnosis, and 5% were diagnosed with GAN, presenting first with gait disturbance. These patients exhibited axonal sensorimotor polyneuropathy and diverse hair types (20% straight, 20% kinky, 40% curly, 20% slightly curly). Findings included carious teeth (40%), hyperplexia (20%), and apnea (20%). Disease progression included worsening scoliosis and limb deformities (pes cavus), with pathological cranial MRI findings. Literature identified 5 GAN patients with a homozygous deletion of GAN gene exon 2-5, classified as likely pathogenic (Class 4). Conclusion: This study highlights the frequency of GAN among undiagnosed polyneuropathies in childhood. Although the phenotype-genotype correlation for giant axonal neuropathy has not yet been determined, we hope that further studies in the field of molecular biology will increase the chances of a better quality of life.

An 8-y-old boy, second born out of a third-degree consanguineous marriage, presented with insidious onset, progressively worsening complaints of frequent falls, swaying while walking, slipping of slippers, and difficulty in buttoning shirt for the past 4 to 5 y. There were no similarly affected members in the family. On examination, his head circumference was appropriate for his age and his hair was thick and curly with a wooly texture (Fig. 1 a & b ). He had mild kyphosis, wasting of thenar and hypothenar eminences, bilateral pes cavus, and prominent calcanei (Fig. 1 c & d ). Neurological examination revealed lower limb predominant distal weakness, distal areflexia, proximal hyporeflexia, abnormal proprioception, and gait ataxia. Nerve conduction studies were suggestive of symmetric length-dependent motor and sensory axonal polyneuropathy. A clinical possibility of inherited motor-sensory axonal polyneuropathy was considered. Genetic analysis revealed a likely pathogenic, autosomal recessive, 2.8 Kb homozygous deletion in the GAN gene (Chr16:81410774-Chr16:81413601), encoding the protein Gigaxonin, confirming the diagnosis of Giant Axonal Neuropathy (GAN). GAN is an autosomal recessive neurodegenerative disorder with onset in the first decade, affecting peripheral and central nervous systems [1] . Loss of functional Gigaxonin, a ubiquitin ligase protein leads to defective turnover and accumulation of intermediate filaments in the cerebral cortex, brainstem, and cerebellum leading to neurodegeneration, and around peripheral nerves, causing the pathognomonic 'giant axons' seen in nerve biopsies. The distinctive thick curly hair is due to the abnormal accumulation of keratin [2] .

We present a 7.5-year-old boy born to a family from the Iranian Azeri Turkish ethnic group with a consanguineous marriage who presents with a unique set of symptoms, suggesting Giant Axonal Neuropathy. He achieved independent walking at age 3 years, with frequent falling during running. Physical and neurological examinations reveal curly blond hair, generalized muscle atrophy, slow speech and difficulty swallowing solid food, foot drop, pes cavus, hammertoe deformities; reduced deep tendon reflexes, clumsy gait, impaired sense of position, and intention tremors.This comprehensive report significantly expands the clinical and mutational spectrum of Giant Axonal Neuropathy. Whole Exome Sequencing (WES) analysis revealed a novel homozygous variant (NC_000016.10(NM_022041.3):c.2T > C) in the GAN gene, confirmed by Sanger sequencing. Segregation analysis showed that the parents were heterozygous for the variant. The variant was absent in a cohort of 430 healthy individuals from the same ethnic group and in other published population databases such as GenomAD and the 1000 Genome. The clinical manifestations, segregation analysis, population study, and bioinformatics analysis collectively confirm the pathogenicity of variant.

Giant Axonal Neuropathy (GAN) is a neurodegenerative disease caused by loss-of-function mutations in the KLHL16 gene, encoding the cytoskeleton regulator gigaxonin. In the absence of functional gigaxonin, intermediate filament (IF) proteins accumulate in neurons and other cell types due to impaired turnover and transport. GAN neurons exhibit distended, swollen axons and distal axonal degeneration, but the mechanisms behind this selective neuronal vulnerability are unknown. Our objective was to identify novel gigaxonin interactors pertinent to GAN neurons. Unbiased proteomics revealed a statistically significant predominance of RNA-binding proteins (RBPs) within the soluble gigaxonin interactome and among differentially-expressed proteins in iPSC-neuron progenitors from a patient with classic GAN. Among the identified RBPs was TAR DNA-binding protein 43 (TDP-43), which associated with the gigaxonin protein and its mRNA transcript. TDP-43 co-localized within large axonal neurofilament IFs aggregates in iPSC-motor neurons derived from a GAN patient with the ‘axonal CMT-plus’ disease phenotype. Our results implicate RBP dysfunction as a potential underappreciated contributor to GAN-related neurodegeneration.

BackgroundGiant axonal neuropathy is a rare, autosomal recessive, pediatric, polysymptomatic, neurodegenerative disorder caused by biallelic loss-of-function variants in GAN, the gene encoding gigaxonin.MethodsWe conducted an intrathecal dose-escalation study of scAAV9/JeT-GAN (a self-complementary adeno-associated virus–based gene therapy containing the GAN transgene) in children with giant axonal neuropathy. Safety was the primary end point. The key secondary clinical end point was at least a 95% posterior probability of slowing the rate of change (i.e., slope) in the 32-item Motor Function Measure total percent score at 1 year after treatment, as compared with the pretreatment slope.ResultsOne of four intrathecal doses of scAAV9/JeT-GAN was administered to 14 participants — 3.5×1013 total vector genomes (vg) (in 2 participants), 1.2×1014 vg (in 4), 1.8×1014 vg (in 5), and 3.5×1014 vg (in 3). During a median observation period of 68.7 months (range, 8.6 to 90.5), of 48 serious adverse events that had occurred, 1 (fever) was possibly related to treatment; 129 of 682 adverse events were possibly related to treatment. The mean pretreatment slope in the total cohort was −7.17 percentage points per year (95% credible interval, −8.36 to −5.97). At 1 year after treatment, posterior mean changes in slope were −0.54 percentage points (95% credible interval, −7.48 to 6.28) with the 3.5×1013–vg dose, 3.23 percentage points (95% credible interval, −1.27 to 7.65) with the 1.2×1014–vg dose, 5.32 percentage points (95% credible interval, 1.07 to 9.57) with the 1.8×1014–vg dose, and 3.43 percentage points (95% credible interval, −1.89 to 8.82) with the 3.5×1014–vg dose. The corresponding posterior probabilities for slowing the slope were 44% (95% credible interval, 43 to 44); 92% (95% credible interval, 92 to 93); 99% (95% credible interval, 99 to 99), which was above the efficacy threshold; and 90% (95% credible interval, 89 to 90). Between 6 and 24 months after gene transfer, sensory-nerve action potential amplitudes increased, stopped declining, or became recordable after being absent in 6 participants but remained absent in 8.ConclusionsIntrathecal gene transfer with scAAV9/JeT-GAN for giant axonal neuropathy was associated with adverse events and resulted in a possible benefit in motor function scores and other measures at some vector doses over a year. Further studies are warranted to determine the safety and efficacy of intrathecal AAV-mediated gene therapy in this disorder. (Funded by the National Institute of Neurological Disorders and Stroke and others; ClinicalTrials.gov number, NCT02362438.)

As a non-classical post-translational modification, O-linked β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation) is widely found in human organ systems, particularly in our brains, and is indispensable for healthy cell biology. With the increasing age of the global population, the incidence of neurodegenerative diseases is increasing, too. The common characteristic of these disorders is the aggregation of abnormal proteins in the brain. Current research has found that O-GlcNAcylation dysregulation is involved in misfolding or aggregation of these abnormal proteins to mediate disease progression, but the specific mechanism has not been defined. This paper reviews recent studies on O-GlcNAcylation's roles in several neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, Machado-Joseph's disease, and giant axonal neuropathy, and shows that O-GlcNAcylation, as glucose metabolism sensor, mediating synaptic function, participating in oxidative stress response and signaling pathway conduction, directly or indirectly regulates characteristic pathological protein toxicity and affects disease progression. The existing results suggest that targeting O-GlcNAcylation will provide new ideas for clinical diagnosis, prevention, and treatment of neurodegenerative diseases.

Giant Axonal Neuropathy (GAN) is a pediatric-neurodegenerative disease caused by KLHL16 mutations. KLHL16 encodes gigaxonin, which regulates intermediate filament turnover. Previous neuropathological studies and examination of postmortem brain tissue in the current study revealed involvement of astrocytes in GAN. To develop a clinically relevant model, we reprogrammed skin fibroblasts from seven GAN patients to pluripotent stem cells (iPSCs), which were used to generate neural progenitor cells (NPCs), astrocytes, and brain organoids. Multiple isogenic control clones were derived via CRISPR/Cas9 gene editing of one patient line carrying the G332R gigaxonin mutation. All GAN iPSCs were deficient for gigaxonin and displayed patient-specific increased vimentin expression. GAN NPCs had lower nestin expression and fewer nestin-positive cells compared with isogenic controls, but nestin morphology was unaffected. GAN brain organoids were marked by the presence of neurofilament and GFAP aggregates. GAN iPSC-astrocytes displayed striking dense perinuclear vimentin and GFAP accumulations and abnormal nuclear morphology. In overexpression systems, GFAP oligomerization and perinuclear aggregation were augmented in the presence of vimentin. GAN patient cells with large perinuclear vimentin aggregates accumulated significantly more nuclear KLHL16 mRNA compared with cells without vimentin aggregates. As an early effector of KLHL16 mutations, vimentin may be a potential target in GAN.

Giant axonal neuropathy (GAN) is caused by mutations in the GAN gene encoding for gigaxonin (GIG), which functions as an adaptor of the CUL3-RBX1-GIG (CRL3GIG) E3 ubiquitin ligase complex. The pathological hallmark of GAN is characterized by the accumulation of densely packed neurofilaments (NFs) in the axons. However, there are fundamental knowledge gaps in our understanding of the molecular mechanisms by which the ubiquitin-proteasome system controls the homeostasis of NF proteins. Recently, the deubiquitylating enzyme USP15 was reported to play a crucial role in regulating ubiquitylation and proteasomal degradation of CRL4CRBN substrate proteins. Here, we report that the CRL3GIG-USP15 pathway governs the destruction of NF proteins NEFL and INA. We identified a specific degron called NEFLL12 degron for CRL3GIG. Notably, mutations in the C-terminal Kelch domain of GIG, represented by L309R, R545C, and C570Y, disrupted the binding of GIG to NEFL and INA, leading to the accumulation of these NF proteins. This accounts for the loss-of-function mutations in GAN patients. In addition to regulating NFs, CRL3GIG also controls actin filaments by directly targeting actin-filament-binding regulatory proteins TPM1, TPM2, TAGLN, and CNN2 for proteasomal degradation. Thus, our findings broadly impact the field by providing fundamental mechanistic insights into regulating extremely long-lived NF proteins NEFL and INA by the CRL3GIG-USP15 pathway and offering previously unexplored therapeutic opportunities to treat GAN patients and other neurodegenerative diseases by explicitly targeting downstream substrates of CRL3GIG.

P445 Electrophysiologic and histologic findings following intrathecal AAV9 mediated gene transfer for giant axonal neuropathy

P444 Ophthalmologic findings following intrathecal AAV9 mediated gene transfer for Giant Axonal Neuropathy

Giant axonal neuropathy (GAN) is a fatal neurodegenerative disorder for which there is currently no treatment. Affecting the nervous system, GAN starts in infancy with motor deficits that rapidly evolve toward total loss of ambulation. Using the gan zebrafish model that reproduces the loss of motility as seen in patients, we conducted the first pharmacological screening for the GAN pathology. Here, we established a multilevel pipeline to identify small molecules restoring both the physiological and the cellular deficits in GAN. We combined behavioral, in silico, and high‐content imaging analyses to refine our Hits to five drugs restoring locomotion, axonal outgrowth, and stabilizing neuromuscular junctions in the gan zebrafish. The postsynaptic nature of the drug's cellular targets provides direct evidence for the pivotal role the neuromuscular junction holds in the restoration of motility. Our results identify the first drug candidates that can now be integrated in a repositioning approach to fasten therapy for the GAN disease. Moreover, we anticipate both our methodological development and the identified hits to be of benefit to other neuromuscular diseases.

Research on pathogenic mechanisms underlying giant axonal neuropathy (GAN), a disease caused by a deficiency of gigaxonin, has been hindered by the lack of appropriate animal models exhibiting substantial symptoms and large neurofilament (NF) swellings, a hallmark of the human disease. It is well established that intermediate filament (IF) proteins are substrates for gigaxonin-mediated degradation. However, it has remained unknown to what extent NF accumulations contribute to GAN pathogenesis. Here, we report the generation of a new mouse model of GAN that is based on crossing transgenic mice overexpressing peripherin (Prph) with mice knockout for Gan The Gan-/-;TgPer mice developed early onset sensory-motor deficits along with IF accumulations made up of NF proteins and of Prph, causing swelling of spinal neurons at a young age. Abundant inclusion bodies composed of disorganized IFs were also detected in the brain of Gan-/-;TgPer mice. At 12 months of age, the Gan-/-;TgPer mice exhibited cognitive deficits as well as severe sensory and motor defects. The disease was associated with neuroinflammation and substantial loss of cortical neurons and spinal neurons. Giant axons (≥160 μm2) enlarged by disorganized IFs, a hallmark of GAN disease, were also detected in dorsal and ventral roots of the Gan-/-;TgPer mice. These results, obtained with both sexes, support the view that the disorganization of IFs can drive some neurodegenerative changes caused by gigaxonin deficiency. This new mouse model should be useful to investigate the pathogenic changes associated with GAN disease and for drug testing.SIGNIFICANCE STATEMENT Research on pathogenic mechanism and treatment of GAN has been hampered by the lack of animal models exhibiting overt phenotypes and substantial neurofilament disorganization, a hallmark of the disease. Moreover, it remains unknown whether neurologic defects associated with gigaxonin deficiency in GAN are because of neurofilament disorganization as gigaxonin may also act on other protein substrates to mediate their degradation. This study reports the generation of a new mouse model of GAN based on overexpression of Prph in the context of targeted disruption of gigaxonin gene. The results support the view that neurofilament disorganization may contribute to neurodegenerative changes in GAN disease. The Gan-/-;TgPer mice provide a unique animal model of GAN for drug testing.