Identification of Novel Compound Heterozygous Mutations in the GAN Gene of a Chinese Patient Diagnosed With Giant Axonal Neuropathy

Giant Axonal Neuropathy: A Case Report of Subclinical Childhood Manifestations

Giant axonal neuropathy (GAN) is a rare, inherited neurodegenerative disease that affects both the central and peripheral nervous systems. It is mostly characterized by a progressive loss of motor and sensory function, which can begin in early childhood. GAN is thought to be caused by a mutation in the GAN gene on chromosome 16q24.1. We report a seven-year-old Saudi male child with GAN who was diagnosed using whole-exome sequencing. The child presented with a history of progressive weakness and muscle wasting in the arms and legs as well as difficulty walking. The sequencing identified a mutation in the GAN gene (NM_022041.3: c.1456G>A). Electrodiagnostic studies showed evidence of diffuse axonal motor and sensory polyneuropathy involving cranial nerves. This case report adds to the growing evidence that whole-exome sequencing can be a useful tool for diagnosing rare inherited neuromuscular disorders. It also highlights the importance of early diagnosis and intervention for this condition.

Expanding the genetic spectrum of giant axonal neuropathy: Two novel variants in Iranian families

BACKGROUND

Giant axonal neuropathy (GAN) is a progressive childhood hereditary polyneuropathy that affects both the peripheral and central nervous systems. Disease-causing variants in the gigaxonin gene (GAN) cause autosomal recessive giant axonal neuropathy. Facial weakness, nystagmus, scoliosis, kinky or curly hair, pyramidal and cerebellar signs, and sensory and motor axonal neuropathy are the main symptoms of this disorder. Here, we report two novel variants in the GAN gene from two unrelated Iranian families.

METHODS

Clinical and imaging data of patients were recorded and evaluated, retrospectively. Whole-exome sequencing (WES) was undertaken in order to detect disease-causing variants in participants. Confirmation of a causative variant in all three patients and their parents was carried out using Sanger sequencing and segregation analysis. In addition, for comparing to our cases, we reviewed all relevant clinical data of previously published cases of GAN between the years 2013-2020.

RESULTS

Three patients from two unrelated families were included. Using WES, we identified a novel nonsense variant [NM_022041.3:c.1162del (p.Leu388Ter)], in a 7-year-old boy of family 1, and a likely pathogenic missense variant [NM_022041.3:c.370T>A (p.Phe124Ile)], in two affected siblings of the family 2. Clinical examination revealed typical features of GAN-1 in all three patients, including walking difficulties, ataxic gait, kinky hair, sensory-motor polyneuropathy, and nonspecific neuroimaging abnormalities. Review of 63 previously reported cases of GAN indicated unique kinky hair, gait problem, hyporeflexia/areflexia, and sensory impairment were the most commonly reported clinical features.

CONCLUSIONS

One homozygous nonsense variant and one homozygous missense variant in the GAN gene were discovered for the first time in two unrelated Iranian families that expand the mutation spectrum of GAN. Imaging findings are nonspecific, but the electrophysiological study in addition to history is helpful to achieve the diagnosis. The molecular test confirms the diagnosis.

Genetic Approaches for the Treatment of Giant Axonal Neuropathy

Giant axonal neuropathy (GAN) is a pediatric, hereditary, neurodegenerative disorder that affects both the central and peripheral nervous systems. It is caused by mutations in the GAN gene, which codes for the gigaxonin protein. Gigaxonin plays a role in intermediate filament (IF) turnover hence loss of function of this protein leads to IF aggregates in various types of cells. These aggregates can lead to abnormal cellular function that manifests as a diverse set of symptoms in persons with GAN including nerve degeneration, cognitive issues, skin diseases, vision loss, and muscle weakness. GAN has no cure at this time. Currently, an adeno-associated virus (AAV) 9-mediated gene replacement therapy is being tested in a phase I clinical trial for the treatment of GAN. This review paper aims to provide an overview of giant axonal neuropathy and the current efforts at developing a treatment for this devastating disease.

Two novel pathogenic mutations of GAN gene identified in a chinese family with giant axonal neuropathy: a case report

BACKGROUND

Giant axonal neuropathy (GAN) is a rare autosomal recessive, early-onset and fatal neurodegenerative disorder which develops into severe impairments in both peripheral and central nervous systems.

METHODS AND RESULTS

Trio-WES analysis was used to detect genetic mutations associated with disorders, and Sanger sequencing was used to confirm the mutations in the patient. We identified two novel variations in GAN gene (c.809G > T(p.G270V); c.1182 C > A(p.Y394X)) within a Chinese family. Meanwhile, we propose a hypothesis of the molecular mechanism leading to GAN.

CONCLUSIONS

This study extend the number of GAN mutations associated with GAN disease and would provide reference for clinical diagnosis in the future.

Giant axonal neuropathy with novel GAN pathogenic variant in a patient of consanguineous origin from Poonch Jammu and Kashmir-India

Giant axonal neuropathy (GAN) is a severe and rare autosomal recessive neurodegenerative disorder of childhood affecting both the peripheral and central nervous systems (CNS). It is caused by mutations in the GAN (gigaxonin) gene linked to chromosome 16q24. Here, we present a 15-year-old male patient with GAN from a consanguineous family of Poonch, Jammu and Kashmir (J&K)-India. Whole-exome sequencing (WES) was employed to unravel the genetic cause of GAN in the proband. Pathogenic variant identified with WES was confirmed in other affected sibling using Sanger sequencing. Magnetic resonance imaging (MRI) and detailed clinical investigation was also carried out on proband. WES revealed a novel homozygous stopgain GAN mutation (NM_022041, c.C1028G, p.S343X) in the patient. MRI of brain displayed bilateral symmetrical confluent areas of deep white matter signal changes affecting periventricular regions (with sparing of subcortical U-fibers), posterior limbs of internal capsules, thalami, external capsules, and semioval centers. The patient was initially suspected to be a case of metachromatic leukodystrophy. However, WES analysis revealed a pathogenic variant in GAN gene as causative. No other pathogenic variant relevant to any other type of dystrophy was reported in WES. Our findings extend the geographical distribution of GAN to even a very remote region in India, extend the mutational and imaging spectrum of GAN and substantiate the need for introducing genetic testing and counselling in primary referral centers/district hospitals in India.