Intrathecal Gene Therapy for Giant Axonal Neuropathy.

BACKGROUND: Giant axonal neuropathy is a rare, autosomal recessive, pediatric, polysymptomatic, neurodegenerative disorder caused by biallelic loss-of-function variants in GAN, the gene encoding gigaxonin. METHODS: We 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. RESULTS: One 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. CONCLUSIONS: Intrathecal 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.).

[Involvement of autonomic nervous system since middle age in elderly patient with giant axonal neuropathy caused by novel genetic mutation].

A 69-year-old man began to experience difficulty with walking at the age of 5 years and started use of a cane at around 13 years, then finally started using a wheelchair at 17 years old. A diagnosis of Charcot-Marie-Tooth disease was previously determined at another hospital, though neither peripheral nerve biopsy nor gene analysis was conducted. He visited our institution at the age of 54 years and irregular outpatient examinations were started, which indicated slowly progressive muscle weakness and sensory disturbance of the limbs, leading to a decline in activities of daily living. Gene analysis at 60 years old identified a novel homozygous missense mutation in the gigaxonin gene, c.1478A>C, p.E493A. Intellectual capacity was preserved and kinky hair was not present, though complications such as vocal cord paralysis, paralytic ileus, and dysarthria were noted starting at age 61. Based on these findings, the patient was diagnosed with a mild form of giant axonal neuropathy.

Características clínicas y respuesta al recambio plasmático terapéutico en los pacientes con síndrome de Guillain Barré / Clinical characteristics and plasma exchange response in Guillain-Barré patients

RESUMEN El objetivo del estudio fue describir las características clínicas, la respuesta al tratamiento y posibles factores asociados de los pacientes con síndrome de Guillain Barré en el Instituto Nacional de Ciencias Neurológicas. Se realizó un estudio descriptivo sobre egresos hospitalarios durante el periodo 2017-2019. La respuesta al tratamiento se evaluó mediante la escala de discapacidad de Hughes. De los 31 pacientes el 61,3% eran varones, y la edad promedio fue de 50 años. Al ingreso, el 87,1% de pacientes se encontraban en el grado 3 o 4 de la escala de Hughes, la mayoría con compromiso axonal, el cual estuvo asociado a discapacidad. Solo 22 pacientes recibieron recambio plasmático; luego de seis meses el 90,9% disminuyó al menos en un grado en la escala de Hughes y el 42,8% quedaron sin discapacidad. En conclusión, se encontró un predominio del sexo masculino y del compromiso axonal, este último asociado a discapacidad.

ABSTRACT The objective of the study was to describe the clinical characteristics, treatment response and possible associated factors of patients with Guillain-Barré syndrome at the National Institute of Neurological Sciences. A descriptive study on hospital discharges was conducted during the period 2017-2019. Treatment response was evaluated based on Hughes' disability scale. From 31 patients 61.3% were males and the mean age was 50 years. At admission, 87.1% of patients were on grade 3 or 4 of Hughes scale, most of them with axonal compromise which was associated to disability. Only 22 patients received plasma exchange; 6 months thereafter, 90.9% of patients decreased by at least one degree in Hughes scale and 42.8% were left without disability. In conclusion, a male and axonal subtype predominance was found, been the latter associated to disability.

Características clínicas y respuesta al recambio plasmático terapéutico en los pacientes con síndrome de Guillain Barré / Clinical characteristics and plasma exchange response in Guillain-Barré patients

RESUMEN El objetivo del estudio fue describir las características clínicas, la respuesta al tratamiento y posibles factores asociados de los pacientes con síndrome de Guillain Barré en el Instituto Nacional de Ciencias Neurológicas. Se realizó un estudio descriptivo sobre egresos hospitalarios durante el periodo 2017-2019. La respuesta al tratamiento se evaluó mediante la escala de discapacidad de Hughes. De los 31 pacientes el 61,3% eran varones, y la edad promedio fue de 50 años. Al ingreso, el 87,1% de pacientes se encontraban en el grado 3 o 4 de la escala de Hughes, la mayoría con compromiso axonal, el cual estuvo asociado a discapacidad. Solo 22 pacientes recibieron recambio plasmático; luego de seis meses el 90,9% disminuyó al menos en un grado en la escala de Hughes y el 42,8% quedaron sin discapacidad. En conclusión, se encontró un predominio del sexo masculino y del compromiso axonal, este último asociado a discapacidad.

ABSTRACT The objective of the study was to describe the clinical characteristics, treatment response and possible associated factors of patients with Guillain-Barré syndrome at the National Institute of Neurological Sciences. A descriptive study on hospital discharges was conducted during the period 2017-2019. Treatment response was evaluated based on Hughes' disability scale. From 31 patients 61.3% were males and the mean age was 50 years. At admission, 87.1% of patients were on grade 3 or 4 of Hughes scale, most of them with axonal compromise which was associated to disability. Only 22 patients received plasma exchange; 6 months thereafter, 90.9% of patients decreased by at least one degree in Hughes scale and 42.8% were left without disability. In conclusion, a male and axonal subtype predominance was found, been the latter associated to disability.

Síndrome de Sjögren primario que debuta con polimiositis mitocondrial, neuropatía axonal y parálisis hipopotasémica: reporte de caso / Onset of primary Sjögren syndrome with mitochondrial polymyositis, axonal neuropathy, and hypokalaemic paralysis: Case report

RESUMEN El síndrome de Sjögren es una entidad multisistémica de naturaleza autoinmune, clásicamente considerada una exocrinopatía debido a la alta frecuencia de síntomas secos (queratoconjuntivitis seca, xerostomía) como resultado de infiltración poliglandular por linfocitos autorreactivos. Sin embargo, menos del 10% de estos pacientes puede iniciar con manifestaciones extraglandulares severas, traducidas en peores desenlaces a largo plazo. Se presenta el caso de una gestante que inició con síndrome de debilidad aguda proximal relacionada con miositis con enfermedad mitocondrial e hipopotasemia severa, en el contexto de acidosis tubular renal distal, como manifestación extraglandular de síndrome de Sjögren primario. Se discuten brevemente manifestaciones neurológicas de esta entidad, incluyendo aquellas secundarias a trastornos metabólicos precipitados por compromiso autoinmune.

ABSTRACT Sjögren's syndrome is a multisystemic autoimmune disorder. It is classically considered as an exocrine disease, given the high frequency of dry symptoms (keratoconjunctivitis sicca, xerostomia) as a result of poly-glandular infiltration by autoreactive lymphocytes. However, less than 10% of these patients can onset with severe extra-glandular manifestations, resulting in worse long-term outcomes. The case of a pregnant woman is presented, who debuted with acute proximal weakness syndrome related to myositis with mitochondrial pathology and severe hypokalaemia in the context of distal renal tubular acidosis, as an extra-glandular manifestation of primary Sjögren's syndrome. Neurological manifestations of this condition are briefly discussed, including those secondary to metabolic disorders precipitated by autoimmune compromise.

Gigaxonin glycosylation regulates intermediate filament turnover and may impact giant axonal neuropathy etiology or treatment

Gigaxonin (also known as KLHL16) is an E3 ligase adaptor protein that promotes the ubiquitination and degradation of intermediate filament (IF) proteins. Mutations in human gigaxonin cause the fatal neurodegenerative disease giant axonal neuropathy (GAN), in which IF proteins accumulate and aggregate in axons throughout the nervous system, impairing neuronal function and viability. Despite this pathophysiological significance, the upstream regulation and downstream effects of normal and aberrant gigaxonin function remain incompletely understood. Here, we report that gigaxonin is modified by O-linked ß-N-acetylglucosamine (O-GlcNAc), a prevalent form of intracellular glycosylation, in a nutrient- and growth factor­dependent manner. MS analyses of human gigaxonin revealed 9 candidate sites of O-GlcNAcylation, 2 of which ­ serine 272 and threonine 277 ­ are required for its ability to mediate IF turnover in gigaxonin-deficient human cell models that we created. Taken together, the results suggest that nutrient-responsive gigaxonin O-GlcNAcylation forms a regulatory link between metabolism and IF proteostasis. Our work may have significant implications for understanding the nongenetic modifiers of GAN phenotypes and for the optimization of gene therapy for this disease.

Two novel mutations in the GAN gene causing giant axonal neuropathy.

BACKGROUND: Giant axonal neuropathy (GAN) is a rare neurodegenerative disease transmitted in an autosomal recessive mode. This disorder presents motor and sensitive symptoms with an onset in early childhood. Progressive neurodegeneration makes the patients wheelchair dependent by the end of the second decade of life. Affected individuals do not survive beyond the third decade of life. Molecular analysis has identified mutations in the gene GAN in patients with this disorder. This gene produces a protein called gigaxonin which is presumably involved in protein degradation via the ubiquitin-proteasome system. However, the underlying molecular mechanism is not clearly understood yet. METHODS: Here we present the first patient from Mexico with clinical data suggesting GAN. Sequencing of the GAN gene was carried out. Changes in the nucleotide sequence were investigated for their possible impact on protein function and structure using the publicly available prediction tools PolyPhen-2 and PANTHER. RESULTS: The patient is a compound heterozygous carrying two novel mutations in the GAN gene. The sequence analysis revealed two missense mutations in the Kelch repeats domain. In one allele, a C>T transition was found in exon 9 at the nucleotide position 55393 (g.55393C>T). In the other allele, a transversion G>T in exon 11 at the nucleotide position 67471 (g.67471G>T) was observed. Both of the bioinformatic tools predicted that these amino acid substitutions would have a negative impact on gigaxonin's function. CONCLUSION: This work provides useful information for health professionals and expands the spectrum of disease-causing mutations in the GAN gene and it is the first documented case in Mexican population.

AAV gene delivery to the spinal cord: serotypes, methods, candidate diseases, and clinical trials.

INTRODUCTION: Adeno-associated viral (AAV) vector-mediated gene delivery to the spinal cord has finally entered the pathway towards regulatory approval. Phase 1 clinical trials using AAV gene therapy for pediatric disorders - spinal muscular atrophy (SMA) and giant axonal neuropathy (GAN) - are now underway. AREAS COVERED: This review addresses the latest progress in the field of AAV gene delivery to the spinal cord, particularly focusing on the most prominent AAV serotypes and delivery methodologies to the spinal cord. Candidate diseases and scaling up experiments in large animals are also discussed. EXPERT OPINION: Intravenous (IV) and intrathecal (IT) deliveries seem to undoubtedly be the preferred routes of administration for diffuse spinal cord delivery of therapeutic AAV vectors that can cross the blood-brain barrier (BBB) and correct inherited genetic disorders. Conversely, intraparenchymal delivery is still an undervalued but very viable approach for segmental therapy in afflictions such as ALS or Pompe Disease as a means to prevent respiratory dysfunction.

Pili canaliculi as manifestation of giant axonal neuropathy

Abstract Giant axonal neuropathy is a rare autosomal recessive neurodegenerative disease. The condition is characterized by neurons with abnormally large axons due to intracellular filament accumulation. The swollen axons affect both the peripheral and central nervous system. A 6-year old female patient had been referred to a geneticist reporting problems with walking and hypotonia. At the age of 10, she became wheelchair dependent. Scanning electron microscopy of a curly hair classified it as pili canaliculi. GAN gene sequencing demonstrated mutation c.1456G>A (p.GLU486LYS). At the age of 12, the patient died due to respiratory complications. Dermatologists should be aware of this entity since hair changes are considered suggestive of GAN.

A review of gigaxonin mutations in giant axonal neuropathy (GAN) and cancer.

Gigaxonin, the product of GAN gene localized to chromosome 16, is associated with the early onset neuronal degeneration disease giant axonal neuropathy (GAN). Gigaxonin is an E3 ubiquitin ligase adaptor protein involved in intermediate filament processing in neural cells, and vimentin filaments in fibroblasts. Mutations of the gene cause pre-neural filaments to accumulate and form giant axons resulting in the inhibition of neural cell signaling. Analysis of the catalog of somatic mutations in cancer, driver DB and IDGC data portal databases containing 21,000 tumor genomic sequences has identified GAN patient mutations in cancer cell lines and primary tumors. The database search has also shown the presence of identical missense and nonsense gigaxonin mutations in GAN and colon cancer. These mutations frequently occur in the domains associated with protein homodimerization and substrate interaction such as Broad-Complex, Tramtrack and Bric a brac (BTB), BTB associated C-terminal KELCH (BACK), and KELCH repeats. Analysis of the International HapMap Project database containing 1200 normal genomic sequences has identified a single nucleotide polymorphism (SNP), rs2608555, in exon 8 of the gigaxonin sequence. While this SNP is present in >40 % of Caucasian population, it is present in less than 10 % of Japanese and Chinese populations. Although the role of gigaxonin polymorphism is not yet known, CFTR and MDR1 gene studies have shown that silent mutations play a role in the instability and aberrant splicing and folding of mRNAs. We believe that molecular and functional investigation of gigaxonin mutations including the exon 8 polymorphism could lead to an improved understanding of the relationship between GAN and cancer.

A mild case of giant axonal neuropathy without central nervous system manifestation.

An 11-year-old boy presented with progressive walking disturbances. He exhibited severe equinovarus feet that together presented with hyperreflexia of the patellar tendon and extensor plantar, resembling spastic paraplegia or upper neuron disease. He showed mild distal muscle atrophy, as well. We did not observe signs of cognitive impairment, cerebellar signs, or brain magnetic resonance imaging abnormalities. Nerve biopsy showed giant axon swellings filled with neurofilaments. Gene analysis revealed novel compound heterozygous missense mutations in the gigaxonin gene, c.808G>A (p.G270S) and c.1727C>A (p.A576E). He was diagnosed with mild giant axonal neuropathy (GAN) without apparent central nervous system involvement. Patients with classical GAN manifest their symptoms during early childhood. Mild GAN, particularly in early stages, can be misdiagnosed because of lack of typical hair features and incomplete or indistinct peripheral and central nervous system symptoms. This case is important since it can aid to identify atypical and milder clinical courses of GAN. This report widens the mild GAN clinical spectrum, alerting physicians for correct diagnosis.

Giant axonal disease: Report of eight cases.

BACKGROUND: Giant axonal neuropathy (GAN) is an autosomal recessive inherited progressive motor and sensory neuropathy with typical onset in early childhood. The disease is caused by GAN gene mutations on chromosome 16q24.1. To determine clinical and genetic results in Turkish patients with GAN. METHODS: Eight children with GAN were retrospectively analyzed. Five (62.5%) were girls and 3 (37.5%) were boys with the mean age on admission 10.13±3.8 years (range: 5-15 years). RESULTS: Parental consanguinity was found in all the families. The patients had the classical clinical phenotype characterized by a severe axonal neuropathy with kinky hair. Two patients had contractures of extremities, and not walking. One patient was walking with aid. The other patients were walking without aid. Mutation analysis was performed in two patients and IVS9 (+1G>T) (homozygous) mutation was detected. CONCLUSION: The classical clinical findings allowed considering the GAN diagnosis, but, in atypical cases and milder phenotypes, the presence of giant axons in nerve biopsy was helpful to specify molecular analysis.

Giant axonal neuropathy.

Giant axonal neuropathy is an autosomal recessive disorder of childhood with distinct morphological features. An 8-year-old boy presented with progressive walking difficulty and recurrent falls. Evaluation showed frizzy hair, characteristic facies, sensory motor neuropathy, and ataxia. Magnetic resonance imaging (MRI) showed bilateral symmetric white matter signal changes in the cerebellum and periventricular regions along with involvement of the posterior limb of the internal capsule. Sural nerve biopsy demonstrated giant axons with neurofilament accumulation. The clinicopathologic manifestations of giant axonal neuropathy are discussed along with the clinical and histologic differential diagnoses.

Giant axonal neuropathy: a rare inherited neuropathy with simple clinical clues.

Giant axonal neuropathy (GAN) is a rare hereditary neurodegenerative disorder characterised by accumulation of excess neurofilaments in the axons of peripheral and central nervous systems, which hampers signal transmission. It usually manifests in infancy and early childhood and is slowly progressive. Those affected with GAN have characteristic curly kinky hair, everted feet and a crouched gait, which suggest the diagnosis in most cases. We describe twin children who presented with difficulty in walking and an abnormal gait since they began walking; clinical clues such as hair changes led us to the final diagnosis.

Ultrasound differentiation of axonal and demyelinating neuropathies.

INTRODUCTION: Ultrasound can be used to visualize peripheral nerve abnormality. Our objective in this study was to prove whether nerve ultrasound can differentiate between axonal and demyelinating polyneuropathies (PNPs). METHODS: Systematic ultrasound measurements of peripheral nerves were performed in 53 patients (25 with demyelinating, 20 with axonal, 8 with mixed neuropathy) and 8 healthy controls. Nerve conduction studies of corresponding nerves were undertaken. RESULTS: Analysis of variance revealed significant differences between the groups with regard to motor conduction velocity, compound muscle action potential amplitude, and cross-sectional area (CSA) of different nerves at different locations. Receiver operating characteristic curve analysis revealed CSA measurements to be well suited for detection of demyelinating neuropathies, and boundary values of peripheral nerve CSA could be defined. CONCLUSIONS: Systematic ultrasound CSA measurement in different nerves helped detect demyelination, which is an additional cue in the etiological diagnosis of PNP, along with nerve conduction studies and nerve biopsy.

Heterogeneity of axonal pathology in Chinese patients with giant axonal neuropathy.

INTRODUCTION: Giant axonal neuropathy (GAN) is a rare autosomal recessive neurodegenerative disorder caused by mutations in the GAN gene. Herein we report ultrastructural changes in Chinese patients with GAN. METHODS: General clinical assessment, sural nerve biopsy, and genetic analysis were performed. RESULTS: Sural biopsy revealed giant axons in 3 patients, 2 with a mild phenotype and 1 with a classical phenotype. Ultrastructurally, all patients had giant axons filled with closely packed neurofilaments. In addition, the classical patient had some axons containing irregular tubular-like structures. GAN mutation analysis revealed novel compound heterozygous c.98A>C and c.158C>T mutations in the BTB domain in 1 mild patient, a novel homozygous c.371T>G mutation in the BACK domain in another mild patient, and a novel c.1342G>T homozygous mutation in the Kelch domain in the classical patient. CONCLUSION: Closely packed neurofilaments in giant axons are common pathological changes in Chinese patients with GAN, whereas irregular tubular-like structures appear in the classical type of this neuropathy.

Giant axonal neuropathy diagnosed on skin biopsy.

Evaluation of hereditary axonal neuropathy in childhood is complex. Often, the child has to be subjected to general anaesthesia for a nerve biopsy to guide further genetic testing, which may or may not be readily available. We describe a toddler with clinical features suggesting giant axonal neuropathy (GAN), whose diagnosis was confirmed by minimally invasive skin biopsy and corroborated by the finding of compound heterozygous mutations involving the GAN gene, including a novel interstitial microdeletion at 16q23.2 detected by microarray and a point mutation detected by direct sequencing.

Giant axonal neuropathy.

Giant axonal neuropathy (GAN) is a rare hereditary autosomal recessive neurodegenerative disease affecting both the peripheral and the central nervous system. Clinically it is characterized by an age of onset during the first decade, progressive and severe motor sensory neuropathy followed, in some patients, by the occurrence of various central nervous system signs such as cerebellar syndrome, upper motor neuron signs, or epilepsy. Although kinky hairs are reported in the majority of patients, it is not a constant finding. The prognosis is usually severe with death occurring during the second or third decade; nevertheless a less severe course is reported in some patients. The presence of a variable number of giant axons filled with neurofilaments in the nerve biopsy represents the pathological feature of the disease and it is usually associated to a variable degree with axonal loss and demyelization. Giant axons are also found in the central nervous system associated with Rosenthal fibers and a variable degree of involvement of white matter and neuronal loss. The disease is caused by mutation in the GAN gene encoding for gigaxonin, a member of BTB-Kelch. Up to now 37 mutations in the GAN gene have been reported. These mutations are scattered over the 11 exons of the gene without a clear genotype-phenotype correlation. These mutations resulting in gigaxonin deficiency lead to a slow down in ubiquitin-mediated protein degradation and possibly of other unidentified proteins. GAN represents a good model of a neurodegenerative disorder in which there is a primary defect of the ubiquitin proteasome system and its network with neurofilaments. The clarification of molecular mechanisms involved in GAN can help in understanding other frequent neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Parkinson disease.

Restoration of cytoskeleton homeostasis after gigaxonin gene transfer for giant axonal neuropathy.

Giant axonal neuropathy (GAN) is caused by loss of function of the gigaxonin protein. On a cellular level GAN is characterized by intermediate filament (IF) aggregation, leading to a progressive and fatal peripheral neuropathy in humans. This study sought to determine if re-introduction of the GAN gene into GAN-deficient cells and mice would restore proper cytoskeleton IF homeostasis. Treatment of primary skin fibroblast cultures from three different GAN patients with an adeno-associated virus type 2 (AAV2) vector containing a normal human GAN transgene significantly reduced the number of cells displaying vimentin IF aggregates. A proteomic analysis of these treated cells was also performed, wherein the abundance of 32 of 780 identified proteins significantly changed in response to gigaxonin gene transfer. While 29 of these responding proteins have not been directly described in association with gigaxonin, three were previously identified as being disregulated in GAN and were now shifted toward normal levels. To assess the potential application of this approach in vivo and eventually in humans, GAN mice received an intracisternal injection of an AAV9/GAN vector to globally deliver the GAN gene to the brainstem and spinal cord. The treated mice showed a nearly complete clearance of peripherin IF accumulations at 3 weeks post-injection. These studies demonstrate that gigaxonin gene transfer can reverse the cellular IF aggregate pathology associated with GAN.

Giant axonal neuropathy caused by a novel compound heterozygous mutation in the gigaxonin gene.

Giant axonal neuropathy is a rare autosomal recessive disorder, which typically involves both central and peripheral nervous system. Yet the phenotypic-genotypic correlation remains obscure. We report a novel compound heterozygous mutation with the c. 805C>T in exon 4(Arg545His missense mutation) and the c. 1634G>A in exon 11(Arg269Trp missense mutation) in an 11-year-old Chinese giant axonal neuropathy case. This patient had an atypical giant axonal neuropathy phenotype rather similar to Charcot-Marie-Tooth disease, without tightly curled hair and mental retardation. The patient had a slowly progressive sensory motor neuropathy since age 3 years, and she also had nystagmus, feet deformities, scoliosis, and cerebellar tonsillar protrusion. Electrophysiological studies indicated a predominantly axonal sensory-motor neuropathy. The diagnosis was confirmed by sural nerve biopsy and direct sequencing of all the 11 gigaxonin exons. The proband's parents are heterozygotes of the disease without symptoms. Our findings extend the number of gigaxonin mutations that cause giant axonal neuropathy.