Hereditary peripheral neuropathies of childhood: an overview for clinicians

Deciphering Auditory Hyperexcitability in Otogl Mutant Mice Unravels an Auditory Neuropathy Mechanism

Auditory neuropathies affect the spiral ganglion neurons of the auditory nerve or their synapses with the sensory hair cells, distorting the sound information transmitted from the ear to the brain. Deciphering the underlying pathophysiological mechanisms remains challenging owing to the diversity of spiral ganglion neuron subtypes and associated central auditory circuits. An auditory neuropathy mechanism is unraveled by investigating the origin of auditory hyperexcitability in a mouse model for hereditary congenital deafness. Otogl encodes the large Otogelin-like protein, which is related to secreted epithelial mucins and is implicated in the mechanical stimulation of cochlear outer hair cells. Heterozygous Otogl+/- mutant mice display auditory hyperexcitability, highlighted by their susceptibility to audiogenic seizures induced by loud sounds. It is shown that Otogl is transiently expressed in a subpopulation of spiral ganglion neurons during cochlear development. Despite their apparently normal hearing, Otogl+/- mice display poor activation of the spiral ganglion neurons processing loud sounds and an elevation of the activation threshold of the middle the ear muscle reflex that attenuates loud sounds. The findings reveal how a neuropathy affecting spiral ganglion neurons specialized in loud sound processing and associated with the middle the ear muscle reflex can manifest itself as auditory hyperexcitability.

Genetic diversity in hereditary axonal neuropathy: Analyzing 53 Brazilian children

BACKGROUND AND AIMS

The genetic epidemiology of inherited neuropathies in children remains largely unknown. In this study, we specifically investigated the genetic profile of a Brazilian cohort of pediatric patients with pure or complex axonal neuropathies, a crucial knowledge in the near future for establishing treatment priorities and perspectives for this group of patients.

METHODS

Fifty-three pediatric patients who were assessed prior to reaching the age of 20, and who had clinical diagnoses of axonal hereditary neuropathy or presented with axonal neuropathy as the primary clinical feature, were included in the study. The recruitment of these cases took place from January 1, 2018, to December 31, 2020. The diagnosis was based on clinical and electrophysiological data. A molecular assessment was made using target-gene panel or whole-exome sequencing. Subsequently, segregation analysis was performed on available family members, and all candidate variants found were confirmed through Sanger.

RESULTS

A molecular diagnosis was reached in 68% of the patients (n = 36/53), considering only pathogenic and probably pathogenic variants. Variants in MFN2 (n = 15) and GJB1 (n = 3) accounted for half of the genetically confirmed patients (50%; n = 18/36). The other 18 genetically diagnosed patients had variants in several less common genes.

INTERPRETATION

Apart from MFN2 and GJB1 genes, universally recognized as a frequent cause of axonal neuropathies in most studied population, our Brazilian cohort of children with axonal neuropathies showed an important genetic heterogeneity, probably reflecting the multi ethnicity of the Brazilian population. Diagnostic, counseling, and future interventions should consider this characteristic.

Demyelination and Na+ Channel Redistribution Underlie Auditory and Vestibular Dysfunction in PMP22-Null Mice

Altered expression of peripheral myelin protein 22 (PMP22) results in demyelinating peripheral neuropathy. PMP22 exhibits a highly restricted tissue distribution with marked expression in the myelinating Schwann cells of peripheral nerves. Auditory and vestibular Schwann cells and the afferent neurons also express PMP22, suggesting a unique role in hearing and balancing. Indeed, neuropathic patients diagnosed with PMP22-linked hereditary neuropathies often present with auditory and balance deficits, an understudied clinical complication. To investigate the mechanism by which abnormal expression of PMP22 may cause auditory and vestibular deficits, we studied gene-targeted PMP22-null mice. PMP22-null mice exhibit an unsteady gait, have difficulty maintaining balance, and live for only ∼3-5 weeks relative to unaffected littermates. Histological analysis of the inner ear revealed reduced auditory and vestibular afferent nerve myelination and profound Na+ channel redistribution without PMP22. Yet, Na+ current density was unaltered, in stark contrast to increased K+ current density. Atypical postsynaptic densities and a range of neuronal abnormalities in the organ of Corti were also identified. Analyses of auditory brainstem responses (ABRs) and vestibular sensory-evoked potential (VsEP) revealed that PMP22-null mice had auditory and vestibular hypofunction. These results demonstrate that PMP22 is required for hearing and balance, and the protein is indispensable for the formation and maintenance of myelin in the peripheral arm of the eighth nerve. Our findings indicate that myelin abnormalities and altered signal propagation in the peripheral arm of the auditory nerve are likely causes of auditory deficits in patients with PMP22-linked neuropathies.

Mutational screening of GDAP1 in dysphonia associated with Charcot-Marie-Tooth disease: clinical insights and phenotypic effects

INTRODUCTION

Mutations in GDAP1 (Ganglioside-induced differentiation-associated protein 1) gene are linked to Charcot-Marie-Tooth disease (CMT), a Heterogenous group of disorders with multiple phenotypes, characterized by peripheral nerve dysfunction that can lead to vocal cord paralysis and diaphragmatic dysfunction.

MAIN BODY

All three affected children of this chosen family have manifested the same clinical symptoms with progressive weakness, mild sensory impairment, and absent tendon reflexes in their early years. Electrodiagnostic analysis displayed an axonal type of neuropathy in affected patients. Sequencing of the GDAP1 gene was requested for all members of the family. Diagnostic assessments included pulmonary and vocal cord function tests, as well as phrenic and peripheral nerve conduction studies. Pathogenicity of GDAP1 variant p.Pro419Leu with axonal CMT2 and autosomal recessive inheritance was confirmed via in silico analysis. Patients with GDAP1 mutations showed dysphonia, speech difficulties, and the characteristic symptoms of CMT. The severity of symptoms correlated with the presence of a type of GDAP1 mutation. Patients with normal vocal cords and pulmonary function exhibited milder symptoms compared to those with GDAP1 mutations. Our study provides clinical insights into the phenotypic effects of GDAP1 mutations in CMT patients. The findings highlight the adverse clinical course and severe disability associated with GDAP1 mutations, including weak limb and laryngeal muscles.

CONCLUSION

Patients with GDAP1 mutations and autosomal recessive neuropathy present with dysphonia and require interventions such as surgery, braces, physical therapy, and exercise. Early diagnosis and comprehensive clinical evaluations are crucial for managing CMT patients with GDAP1 mutations.

Neurogenetic motor disorders

Advances in the field of neurogenetics have practical applications in rapid diagnosis on blood and body fluids to extract DNA, obviating the need for invasive investigations. The ability to obtain a presymptomatic diagnosis through genetic screening and biomarkers can be a guide to life-saving disease-modifying therapy or enzyme replacement therapy to compensate for the deficient disease-causing enzyme. The benefits of a comprehensive neurogenetic evaluation extend to family members in whom identification of the causal gene defect ensures carrier detection and at-risk counseling for future generations. This chapter explores the many facets of the neurogenetic evaluation in adult and pediatric motor disorders as a primer for later chapters in this volume and a roadmap for the future applications of genetics in neurology.

A case for genomic medicine in South African paediatric patients with neuromuscular disease

Paediatric neuromuscular diseases are under-recognised and under-diagnosed in Africa, especially those of genetic origin. This may be attributable to various factors, inclusive of socioeconomic barriers, high burden of communicable and non-communicable diseases, resource constraints, lack of expertise in specialised fields and paucity of genetic testing facilities and biobanks in the African population, making access to and interpretation of results more challenging. As new treatments become available that are effective for specific sub-phenotypes, it is even more important to confirm a genetic diagnosis for affected children to be eligible for drug trials and potential treatments. This perspective article aims to create awareness of the major neuromuscular diseases clinically diagnosed in the South African paediatric populations, as well as the current challenges and possible solutions. With this in mind, we introduce a multi-centred research platform (ICGNMD), which aims to address the limited knowledge on NMD aetiology and to improve genetic diagnostic capacities in South African and other African populations.

Sibling Cases of Charcot-Marie-Tooth Disease Type 4H with a Homozygous FGD4 Mutation and Cauda Equina Thickening

Charcot-Marie-Tooth disease type 4H (CMT4H) is an autosomal recessive inherited demyelinating neuropathy caused by an FYVE, RhoGEF, and a PH domain-containing protein 4 (FGD4) gene mutation. CMT4H is characterized by an early onset, slow progression, scoliosis, distal muscle atrophy, and foot deformities. We herein present sibling cases of CMT4H with a homozygous mutation in the FGD4 gene. Both patients exhibited cauda equina thickening on magnetic resonance imaging, which had not been reported among the previous CMT4H cases. This is the first report of CMT4H with a homozygous FGD4 c.1730G>A (p.Arg577Gln) mutation showing mild progression and cauda equina thickening.

Differential Diagnosis of Acquired and Hereditary Neuropathies in Children and Adolescents-Consensus-Based Practice Guidelines

Disorders of the peripheral nerves can be caused by a broad spectrum of acquired or hereditary aetiologies. The objective of these practice guidelines is to provide the reader with information about the differential diagnostic workup for a target-oriented diagnosis. Following an initiative of the German-speaking Society of Neuropaediatrics, delegates from 10 German societies dedicated to neuroscience worked in close co-operation to write this guideline. Applying the Delphi methodology, the authors carried out a formal consensus process to develop practice recommendations. These covered the important diagnostic steps both for acquired neuropathies (traumatic, infectious, inflammatory) and the spectrum of hereditary Charcot-Marie-Tooth (CMT) diseases. Some of our most important recommendations are that: (i) The indication for further diagnostics must be based on the patient's history and clinical findings; (ii) Potential toxic neuropathy also has to be considered; (iii) For focal and regional neuropathies of unknown aetiology, nerve sonography and MRI should be performed; and (iv) For demyelinated hereditary neuropathy, genetic diagnostics should first address PMP22 gene deletion: once that has been excluded, massive parallel sequencing including an analysis of relevant CMT-genes should be performed. This article contains a short version of the guidelines. The full-length text (in German) can be found at the Website of the "Arbeitsgemeinschaft der Wissenschftlichen Medizinischen Fachgesellschaften e.V. (AWMF), Germany.

Emerging Therapies for Charcot-Marie-Tooth Inherited Neuropathies

Inherited neuropathies known as Charcot-Marie-Tooth (CMT) disease are genetically heterogeneous disorders affecting the peripheral nerves, causing significant and slowly progressive disability over the lifespan. The discovery of their diverse molecular genetic mechanisms over the past three decades has provided the basis for developing a wide range of therapeutics, leading to an exciting era of finding treatments for this, until now, incurable group of diseases. Many treatment approaches, including gene silencing and gene replacement therapies, as well as small molecule treatments are currently in preclinical testing while several have also reached clinical trial stage. Some of the treatment approaches are disease-specific targeted to the unique disease mechanism of each CMT form, while other therapeutics target common pathways shared by several or all CMT types. As promising treatments reach the stage of clinical translation, optimal outcome measures, novel biomarkers and appropriate trial designs are crucial in order to facilitate successful testing and validation of novel treatments for CMT patients.

Genetic mechanisms of peripheral nerve disease

Peripheral neuropathies of genetic etiology are a very diverse group of disorders manifesting either as non-syndromic inherited neuropathies without significant manifestations outside the peripheral nervous system, or as part of a systemic or syndromic genetic disorder. The former and most frequent group is collectively known as Charcot-Marie-Tooth disease (CMT), with prevalence as high as 1:2,500 world-wide, and has proven to be genetically highly heterogeneous. More than 100 different genes have been identified so far to cause various CMT forms, following all possible inheritance patterns. CMT causative genes belong to several common functional pathways that are essential for the integrity of the peripheral nerve. Their discovery has provided insights into the normal biology of axons and myelinating cells, and has highlighted the molecular mechanisms including both loss of function and gain of function effects, leading to peripheral nerve degeneration. Demyelinating neuropathies result from dysfunction of genes primarily affecting myelinating Schwann cells, while axonal neuropathies are caused by genes affecting mostly neurons and their long axons. Furthermore, mutation in genes expressed outside the nervous system, as in the case of inherited amyloid neuropathies, may cause peripheral neuropathy resulting from accumulation of β-structured amyloid fibrils in peripheral nerves in addition to various organs. Increasing insights into the molecular-genetic mechanisms have revealed potential therapeutic targets. These will enable the development of novel therapeutics for genetic neuropathies that remain, in their majority, without effective treatment.

An adapted dance program for children with Charcot-Marie-Tooth disease: An exploratory study

BACKGROUND

Charcot-Marie-Tooth disease (CMT) is a rare hereditary peripheral neuropathy. Its sensorimotor clinical manifestations are heterogeneous, and it might also influence cognitive functions. Physical activity is recommended for adults with CMT, however there is a lack of studies focusing on the effects of physical activity in children with CMT. Dance practice is beneficial for motor and cognitive functions. Adapted dance is interesting for children with CMT because it could address the functional deficits.

OBJECTIVES

To evaluate the feasibility of an adapted dance program and to explore its effects on motor and cognitive functions in children with CMT.

METHODS

Five children with CMT followed a 10-week dance program added to regular care, while four others received only regular care. Feasibility of the program was assessed by participation and retention rates. Motor (CMT clinical characteristics, muscular force and power, postural control, pain) and cognitive (rhythm task, sustained attention, short term memory) abilities were evaluated before and after the program.

RESULTS

The high participation and retention rates (89% and 100%) suggest that a dance program is feasible in children with CMT. Significant benefits were noted for both motor (CMT clinical characteristics, strength of leg muscle groups, pain during physical activity) and cognitive (rhythm task, attention) functions for the dance group.

CONCLUSION

The results suggest that an adapted dance program is feasible and can have beneficial effects on motor and cognitive functions of children with CMT. Dance appears as a new approach adapted for these children. Further research is needed to confirm these results.

Case series: Childhood Charcot-Marie-Tooth: Predominance of axonal subtype

Case series reports on clinical features of pediatric hereditary neuropathy in Thailand is scarce. Subtype and clinical presentation in childhood-onset CMT differ from adult-onset. The aim of this study is to investigate the CMT phenotype in Thai children.

We retrospectively reviewed children diagnosed with CMT who followed up with Pediatric Neurology, Siriraj Hospital from January 1999 to June 2016. CMT subtypes determined by clinical presentation and neurophysiologic studies. Mutation analysis of PMP22 genes was performed in all demyelinating cases. The disease burden was assessed by CMT Neuropathy Score version 2 (CMTNSv2), CMT Examination Score (CMTES) and CMT Pediatric Scale (CMTPedS). 30 patients from 29 families with Hereditary Neuropathies, 25 diagnosed with CMT and 5 with HSAN. 8-year-old was the average age at first medical visit with disease-related problems. Twenty (67%) were male. Twenty-three were sporadic (77%). 16.7% was autosomal dominant and 6.7% was autosomal recessive. Clinical presentations in CMT children were walking difficulty and foot deformities. Nine (36%) CMT patients had demyelinating and sixteen (64%) had axonal. Forty percent had a history of delayed walking after 15-month-old. Foot deformities presented in all CMT patients, and twelve had foot surgery. 2 axonal CMT patients were wheelchair-dependence. Mean (SD) CMTNSv2, CMTES and CMTPedS were 15.44(9), 11.05(7) and 34(4) respectively. Our findings suggest Thai CMT children are predominantly axonal type. Patients with low socioeconomic status and mild symptoms may not seek healthcare. International collaboration in genetic testing is crucial in diagnosis and initiation of clinical trials in future.

•

Thai CMT children are predominantly axonal type.

•

There is much higher incidence of HSAN among CMT children at our institution.

•

International collaboration in genetic testing is crucial in diagnosis and initiation of clinical trials in future.

Hereditary Neuropathies

BACKGROUND

Hereditary peripheral neuropathies constitute a large group of genetic diseases, with an overall prevalence of 1:2500. In recent years, the use of so-called next-generation sequencing (NGS) has led to the identification of many previously unknown involved genes and genetic defects that cause neuropathy. In this article, we review the procedures and utility of genetic evaluation for hereditary neurop - athies, while also considering the implications of the fact that causally directed treatment of these disorders is generally unavailable.

METHODS

This review is based on pertinent publications retrieved by a PubMed search employing the search terms "hereditary neuropathy," "Charcot-Marie-Tooth disease," "hereditary sensory neuropathy," and "hereditary motor neuropathy."

RESULTS

With rare exceptions, the diagnostic evaluation for hereditary neuropathies proceeds in stepwise fashion, beginning with the study of individual genes. If this fails to detect any abnormality, NGS analysis, which involves the sequencing of many different genes in parallel and has now become available for routine diagnosis, should be performed early on in the diagnostic work-up. Exome and genome analyses are currently performed only when considered to be indicated in the individual case. Whenever a hereditary neuropathy is suspected, other (including potentially treatable) causes of neuropathy should be ruled out. Mutations in neurop athy-associated genes may also be associated with other clinical entities such as spastic paraplegia or myopathy. Thus, interdisciplinary assessment is necessary.

CONCLUSION

The molecular diagnosis of neuropathies has become much more successful through the use of NGS. Although causally directed treatment approaches still need to be developed, the correct diagnosis puts an end to the often highly stressful search for a cause and enables determination of the risk of disease in other members of the patient's family.

Novel GDAP1 Mutation in a Vietnamese Family with Charcot-Marie-Tooth Disease

Background

Mutations of GDAP1 gene cause autosomal dominant and autosomal recessive Charcot-Marie-Tooth (CMT) disease and over 80 different mutations have been identified so far. This study analyzed the clinical and genetic characteristics of a Vietnamese CMT family that was affected by a novel GDAP1 mutation.

Methods

We present three children of a family with progressive weakness, mild sensory loss, and absent tendon reflexes. Electrodiagnostic analyses displayed an axonal type of neuropathy in affected patients. Sequencing of GDAP1 gene was requested for all members of the family.

Results

All affected individuals manifested identical clinical symptoms of motor and sensory impairments within the first three years of life, and nerve conduction study indicated the axonal degeneration. A homozygous GDAP1 variant (c.667_671dup) was found in the three affected children as recessive inheritance pattern. The mutation leads to a premature termination codon that shortens GDAP1 protein (p.Gln224Hisfs∗37). Further testing showed heterozygous c.667_671dup variant in the parents.

Discussion

Our study expands the mutational spectrum of GDAP1-related CMT disease with the new and unreported GDAP1 variant. Alterations in GDAP1 gene should be evaluated as CMT causing variants in the Vietnamese population, predominantly axonal form of neuropathy in CMT disease.

Charcot-Marie-Tooth disease with pyramidal features due to a new mutation of EGR2 gene

Background and aim of the work: Childhood-onset peripheral neuropathies are often of genetic origin. Charcot-Marie-Tooth (CMT), is considered the commonest neuromuscular disorder. Due to its high clinical heterogeneity, especially in the pediatric age, the co-existence of central and peripheral symptoms and signs does not necessarily rule out a diagnosis of hereditary peripheral neuropathy. Methods: We describe the clinical, neurophysiological and genetic findings in a teen-age patient evaluated for acquired toe-walking and progressive difficulties in walking since the age of 5. Genetic testing was carried out with a targeted NGS panel. Identified variants are analyzed using Variant Studio program (Illumina). Rare variants and variants considered as pathogenic were analyzed by Sanger direct sequencing. Results: The coexistence ofperipheral and pyramidal signs in the lower limbs, the absence of a significant pre/perinatal history, the unremarkable brain and spine MRI, together with the presence of a sensory-motor polyneuropathy in all four limbs, prompted the execution of genetic investigations with an NGS panel covering hereditary spastic paraplegias, motor neuron disease and Charcot-Marie-Tooth. We identified a previously undescribed variant (c.1142G>T, p.Arg381Leu) in the EGR2 gene. Conclusions:ERG2 gene has been described as a cause of various phenotypes, including a rare autosomal dominant form of CMT (CMT type 1D) representing approximately 1% of all CMT subgroups. We describe a novel pathogenic variant in EGR2 gene leading to the development of a complex association of peripheral and central neurological signs, underscoring the genetic and clinical heterogeneity of hereditary neuropathies of pediatric onset. (www.actabiomedica.it)

Unique clinical and neurophysiologic profile of a cohort of children with CMTX3

OBJECTIVE

To describe in detail the clinical profile of Charcot-Marie-Tooth disease subtype 3 (CMTX3) to aid appropriate genetic testing and rehabilitative therapy.

METHODS

We reviewed the clinical and neurophysiologic profile and CMT Pediatric Scale (CMTPedS) assessments of 11 children with CMTX3.

RESULTS

Compared with the more common forms of CMT, CMT1A and CMTX, CMTX3 was characterized by early onset with early and progressive hand weakness. Most affected children were symptomatic within the first 2 years of life. The most common presentation was foot deformity in the first year of life. CMTPedS analysis in these children revealed that CMTX3 progressed more rapidly (4.3 ± 4.1 points over 2 years, n = 7) than CMT1A and CMTX1. Grip strength in affected boys was 2 SDs below age- and sex-matched normative reference values (z score -2.05 ± 1.32) in the second decade of life. The most severely affected individual was wheelchair bound at 14 years of age, and 2 individuals had no movement in the small muscles of the hand in the second decade of life. Nerve conduction studies showed a demyelinating sensorimotor neuropathy with motor conduction velocity ≤23 m/s.

CONCLUSIONS

CMTX3 had an earlier onset, severe hand weakness, and more rapidly progressive disability compared to the more common forms of CMT. Understanding the unique phenotype of CMTX3 is essential for directing genetic testing because the CMTX3 insertion will not be seen on a routine microarray or neuromuscular gene panel. Early diagnosis will enable rehabilitation to be started early in this rapidly progressive neuropathy.

Correlation between serum vitamin B12 level and peripheral neuropathy in atrophic gastritis

AIM

To explore the correlation between serum vitamin B12 level and peripheral neuropathy in patients with chronic atrophic gastritis (CAG).

METHODS

A total of 593 patients diagnosed with chronic gastritis by gastroscopy and pathological examination from September 2013 to September 2016 were selected for this study. The age of these patients ranged within 18- to 75-years-old. Blood pressure, height and weight were measured in each patient, and the body mass index value was calculated. Furthermore, gastric acid, serum gastrin, serum vitamin and serum creatinine tests were performed, and peripheral nerve conduction velocity and Helicobacter pylori (H. pylori) were detected. In addition, the type of gastritis was determined by gastroscopy. The above factors were used as independent variables to analyze chronic gastritis with peripheral neuropathy and vitamin B12 deficiency risk factors, and to analyze the relationship between vitamin B12 levels and peripheral nerve conduction velocity. In addition, in the treatment of CAG on the basis of vitamin B12, patients with peripheral neuropathy were observed.

RESULTS

Age, H. pylori infection, CAG, vitamin B9 and vitamin B12 were risk factors for the occurrence of peripheral nerve degeneration. Furthermore, CAG and H. pylori infection were risk factors for chronic gastritis associated with vitamin B12 deficiency. Serum vitamin B12 level was positively correlated with sensory nerve conduction velocity in the tibial nerve (R = 0.463). After vitamin B12 supplementation, patients with peripheral neuropathy improved.

CONCLUSION

Serum vitamin B12 levels in patients with chronic gastritis significantly decreased, and the occurrence of peripheral neuropathy had a certain correlation. CAG and H. pylori infection are risk factors for vitamin B12 deficiency and peripheral neuropathy. When treating CAG, vitamin B12 supplementation can significantly reduce peripheral nervous system lesions. Therefore, the occurrence of peripheral neuropathy associated with vitamin B12 deficiency may be considered in patients with CAG. Furthermore, the timely supplementation of vitamin B12 during the clinical treatment of CAG can reduce or prevent peripheral nervous system lesions.

Diseases of the peripheral nerves

This chapter reviews the diseases of the peripheral nerves from a neuropathologic point of view, with a special focus on specific morphologic changes, and includes a summary of the histopathologic methods available for their diagnosis. As the rate of obesity and the prevalence of type 2 diabetes increase, diabetic neuropathy is the most common cause of peripheral neuropathy. Many systemic disorders with metabolic origin, like amyloidosis, hepatic failure, vitamin deficiencies, uremia, lipid metabolism disorders, and others, can also cause axonal or myelin alterations in the peripheral nervous system. The most notable causes of toxic neuropathies are chemotherapeutic agents, alcohol consumption, and exposure to heavy metals and other environmental or biologic toxins. Inflammatory neuropathies cover infectious neuropathies (Lyme disease, human immunodeficiency virus, leprosy, hepatitis) and neuropathies of autoimmune origin (sarcoidosis, Guillain-Barré syndrome/acute inflammatory demyelinating polyneuropathy, chronic inflammatory demyelinating polyneuropathy, and diverse forms of vasculitis. The increasing number of known diseases causing gene mutations in hereditary peripheral neuropathies requires precise characterization, which includes histopathology.

Hereditary neuropathy with liability to pressure palsy (HNPP): report of a family with a new point mutation in PMP22 gene

Background

Hereditary neuropathy with liability to pressure palsy (HNPP) is an autosomal dominant disorder most commonly presenting with acute-onset, non-painful focal sensory and motor mononeuropathy. Approximately 80% of patients carry a 1.5 Mb deletion of chromosome 17p11.2 involving the peripheral myelin protein 22 gene (PMP22), the same duplicated in Charcot-Marie-Tooth 1A patients. In a small proportion of patients the disease is caused by PMP22 point mutations.

Case presentation

We report on a familial case harbouring a new point mutation in the PMP22 gene.

The proband is a 4-years-old girl with acute onset of focal numbness and weakness in her right hand. Electroneurography demonstrated transient sensory and motor radial nerves involvement. In her father, reporting chronic symptoms (cramps and exercise-induced myalgia), we uncovered mild atrophy and areflexia on clinical examination and a mixed (predominantly demyelinating) polyneuropathy with sensory-motor involvement on electrophysiological study.

Both carried a nucleotidic substitution c.178 + 2 T > C on intron 3 of the PMP22 gene, involving the splicing donor site, not reported on databases but predicted to be likely pathogenic.

Conclusions

We described a previously unreported point mutation in PMP22 gene, which led to the development of a HNPP phenotype in a child and her father. In children evaluated for a sensory and motor transient episode, HNPP disorder due to PMP22 mutations should be suspected. Clinical and electrophysiological studies should be extended to all family members even in the absence of previous episodes suggestive for HNPP.

Towards a functional pathology of hereditary neuropathies

A growing number of hereditary neuropathies have been assigned to causative gene defects in recent years. The study of human nerve biopsy samples has contributed substantially to the discovery of many of these neuropathy genes. Genotype-phenotype correlations based on peripheral nerve pathology have provided a comprehensive picture of the consequences of these mutations. Intriguingly, several gene defects lead to distinguishable lesion patterns that can be studied in nerve biopsies. These characteristic features include the loss of certain nerve fiber populations and a large spectrum of distinct structural changes of axons, Schwann cells and other components of peripheral nerves. In several instances the lesion patterns are directly or indirectly linked to the known functions of the mutated gene. The present review is designed to provide an overview on these characteristic patterns. It also considers other aspects important for the manifestation and pathology of hereditary neuropathies including the role of inflammation, effects of chemotherapeutic agents and alterations detectable in skin biopsies.

Congenital insensitivity to pain with anhidrosis: A report of two siblings with a novel mutation in (TrkA) NTRK1 gene in a Saudi family

Congenital insensitivity to pain with anhidrosis (CIPA) or hereditary sensory and autonomic neuropathy type IV (HSAN type IV) is an extremely rare autosomal recessive disorder with an estimated incidence of 1 in 25,000. It was first described in 1963, and since then several case reports and review articles have been published. In this article, we report two brothers with clinical features of CIPA, who presented with recurrent episodes of hyperthermia, anhidrosis, profound loss of pain sensitivity, and unconscious self-mutilation of fingers, lip and tongue. Sanger sequencing analysis confirmed the presence of a novel mutation c.783_785delGAA in the NTRK1 gene in the two affected members of the family. Early diagnosis and management of different systemic complications including orthopedic, visual, and dental may be useful in the reduction of frequency and severity of these complications.

Feeding and Swallowing Disorders in Pediatric Neuromuscular Diseases: An Overview

Feeding and swallowing problems in infants and children have a great impact on health and wellbeing. The aim of this study was to provide an overview of recognized feeding and swallowing problems in different groups of children with neuromuscular diseases, based on relevant literature and expert opinion, and to propose recommendations for the assessment and treatment of these problems. Almost all pediatric neuromuscular diseases are accompanied by feeding and swallowing problems during the different phases of deglutition, problems that give rise to a wide variety of signs and symptoms, which emphasizes the importance of a comprehensive feeding and swallowing assessment by a speech and language therapist.

Charcot-Marie-Tooth diseases: an update and some new proposals for the classification

BACKGROUND

Charcot-Marie-Tooth (CMT) disease, the most frequent form of inherited neuropathy, is a genetically heterogeneous group of disorders of the peripheral nervous system, but with a quite homogeneous clinical phenotype (progressive distal muscle weakness and atrophy, foot deformities, distal sensory loss and usually decreased tendon reflexes). Our aim was to review the various CMT subtypes identified at the present time.

METHODS

We have analysed the medical literature and performed a historical retrospective of the main steps from the individualisation of the disease (at the end of the nineteenth century) to the recent knowledge about CMT.

RESULTS

To date, >60 genes (expressed in Schwann cells and neurons) have been implicated in CMT and related syndromes. The recent advances in molecular genetic techniques (such as next-generation sequencing) are promising in CMT, but it is still useful to recognise some specific clinical or pathological signs that enable us to validate genetic results. In this review, we discuss the diagnostic approaches and the underlying molecular pathogenesis.

CONCLUSIONS

We suggest a modification of the current classification and explain why such a change is needed.

[A novel mutation in glycyl-tRNA synthetase caused Charcot-Marie-Tooth disease type 2D with facial and respiratory muscle involvement]

BACKGROUND

Charcot-Marie-Tooth disease (CMT) is a hereditary peripheral neuropathy; symptoms include distal wasting and weakness, usually with some sensory impairment. The clinical course is typically benign and the disease is not life threatening; however, in some cases, severe phenotypes include serious respiratory distress.

CASE REPORT

Here we describe a 45-year-old woman with a long course of motor-dominant neuropathy. Distal weakness appeared in childhood and became worse with age. After a diagnosis of CMT type 2, the symptoms progressed, and in her fourth decade, facial and respiratory muscle weakness appeared, ultimately requiring non-invasive mechanical ventilation. There was no family history of CMT. Comprehensive analysis of known CMT-related genes revealed a novel heterozygous c.815T>A, p.L218Q mutation in glycyl-tRNA synthetase (GARS), a causative gene for both CMT type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V). This mutation was considered pathogenic based on molecular evidence; notably, it was unique in that all other reported GARS mutations associated with severe phenotypes are located in an anticodon-binding domain, while in this case in an apparently non-functional region of the GARS gene. Not a simple loss-of-function mechanism, but rather gain-of-function mechanisms have also been reported in GARS mutations. This case provided useful information for understanding the mechanism of CMT2D/dSMA-V.

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.

Pediatric Charcot-Marie-Tooth disease

Heritable diseases of the peripheral nerves (Charcot-Marie-Tooth disease [CMT]) affect the motor units and sensory nerves, and they are among the most prevalent genetic conditions in the pediatric patient population. The typical clinical presentation includes distal muscle weakness and atrophy, but the severity and progression are largely variable. Improvements in supportive treatment have led to better preservation of patients' motor functions. More than 80 genes have been associated with CMT. These genetic discoveries, along with the developments of cellular and transgenic disease models, have allowed clinicians to better understand the disease mechanisms, which should lead to more specific treatments.

Molecular and clinical features of inherited neuropathies due to PMP22 duplication

PMP22 is a transmembrane glycoprotein component of myelin, important for myelin functioning. Mutation of PMP22 gene which encodes for the production of PMP22 glycoprotein is associated with a variety of inherited neuropathies. This literature review sought to review the molecular mechanism and clinical features of inherited neuropathies caused by PMP22 duplication. PMP22 duplication causes CMT1A which accounts for more than half of all CMT cases and about 70% of CMT1 cases. It manifests with muscle weakness, depressed reflexes, impaired distal sensation, hand and foot deformities, slowing of NCV and onion bulbs. With no specific treatment available, it is managed conservatively. Future treatment may be based on the molecular genetics of the disease.

Etiologic spectrum of biopsy-proven peripheral neuropathies in childhood from a resource-poor setting

There are only a few studies describing the etiologic spectrum of biopsy-proven peripheral neuropathies in children. This study reviewed the clinical, electrophysiological, and pathologic profile of 239 children (≤18 years of age) who have undergone nerve biopsy in a tertiary care centre for neurologic disorders and analyzed the etiologic spectrum and utility of nerve biopsy. The clinical profile, neuropathologic findings, and other investigations were combined to infer the final diagnosis. Neuropathy was detected in 199 biopsies; axonal pathology in 43%; demyelination in 41%; mixed pattern in 8%; and nonspecific findings in 8%. The major diagnostic categories included hereditary neuropathies (48%), heredodegenerative and metabolic disorders (27%), and inflammatory neuropathies (12%). Nerve biopsy proved most helpful in diagnosis of demyelinating and inflammatory neuropathies, reiterating its usefulness in specific situations.

Auditory neuropathy spectrum disorder: a review

PURPOSE

Auditory neuropathy spectrum disorder, or ANSD, can be a confusing diagnosis to physicians, clinicians, those diagnosed, and parents of children diagnosed with the condition. The purpose of this review is to provide the reader with an understanding of the disorder, the limitations in current tools to determine site(s) of lesion, and management techniques.

METHOD

This article is a review of what is known about ANSD. It includes descriptions of assessment tools, causes of ANSD, and patient management techniques.

CONCLUSIONS

This review is a guide to audiologists, speech-language pathologists, and early interventionists who work with individuals diagnosed with ANSD and/or their families. It highlights the need for more precise tools to describe the disorder in order to facilitate decisions about interventions and lead to better predictions of outcome.

Whole exome sequencing identifies three recessive FIG4 mutations in an apparently dominant pedigree with Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT) is genetically heterogeneous and classification based on motor nerve conduction velocity and inheritance is used to direct genetic testing. With the less common genetic forms of CMT, identifying the causative genetic mutation by Sanger sequencing of individual genes can be time-consuming and costly. Next-generation sequencing technologies show promise for clinical testing in diseases where a similar phenotype is caused by different genes. We report the unusual occurrence of CMT4J, caused by mutations in FIG4, in a apparently dominant pedigree. The affected proband and her mother exhibit different disease severities associated with different combinations of compound heterozygous FIG4 mutations, identified by whole exome sequencing. The proband was also shown to carry a de novo nonsense mutation in the dystrophin gene, which may contribute to her more severe phenotype. This study is a cautionary reminder that in families with two generations affected, explanations other than dominant inheritance are possible, such as recessive inheritance due to three mutations segregating in the family. It also emphasises the advantages of next-generation sequencing approaches that screen multiple CMT genes at once for patients in whom the common genes have been excluded.

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.

Deficiency of the E3 ubiquitin ligase TRIM2 in early-onset axonal neuropathy

Inherited peripheral neuropathies are a heterogeneous group of disorders that can affect patients of all ages. Children with inherited neuropathy often develop severe disability, but the genetic causes of recessive early-onset axonal neuropathies are not fully known. We have taken a whole-exome sequencing approach to identify causative disease mutations in single patients with early-onset axonal neuropathy. Here, we report compound heterozygous mutations in the tripartite motif containing 2 (TRIM2) gene in a patient with childhood-onset axonal neuropathy, low weight and small muscle mass. We show that the patient fibroblasts are practically devoid of TRIM2, through mRNA and protein instability caused by the mutations. TRIM2 is an E3 ubiquitin ligase that ubiquitinates neurofilament light chain, a component of the intermediate filament in axons. Resembling the findings in our patient's sural nerve biopsy, Trim2-gene trap mice showed axonopathy with accumulations of neurofilaments inside axons. Our results suggest that loss-of-function mutations in TRIM2 are a cause of axonal neuropathy, which we propose to develop as a consequence of axonal accumulation of neurofilaments, secondary to lack of its ubiquitination by TRIM2.

The first Japanese case of Charcot-Marie-Tooth disease type 4H with a novel FGD4 c.837-1G>A mutation

Charcot-Marie-Tooth disease type 4H (CMT4H) is an autosomal recessive demyelinating neuropathy. It presents as infancy or early childhood-onset neuropathy associated with FGD4 mutations. Clinically it causes predominantly distal muscle weakness. On nerve biopsy examination, myelin outfoldings are seen. The previous case reports have been from regions bordering the Mediterranean, as well as a family from Northern Ireland. This paper presents the detailed clinical course of the first reported case of CMT4H in a Japanese woman. The patient showed mild weakness without scoliosis and a severe sensory disturbance; her functional impairment was less severe than the previously published cases. In addition, a novel homozygous FGD4 c.837-1G>A mutation was identified in this patient.

Diagnosis and management of pediatric peripheral neuropathies in resource-poor settings

The diagnosis of a peripheral neuropathy in a child who resides in the majority of resource-poor settings is based on the history taken and the clinical examination. The majority of children, unless they demonstrate additional clinical markers, will lack a more definitive diagnosis beyond the label ‘peripheral neuropathy’. The treatable, typically acquired conditions, which are prevalent in these settings, are the priority to identify. This would include neuroinfections, neuroinflammation, toxins and vitamin deficiencies. The management of children with peripheral neuropathies in resource-poor settings must be approached in a different manner to that of more ‘resource-equipped’ settings. Secondary or tertiary centers are scarce, often significant distances away from the patient, and this leads to long delays before access is possible. Most children present to primary healthcare settings and are seen by practitioners with little training in the features suggestive of a peripheral neuropathy. As such, basic aids to assist the healthcare worker in the early recognition and interventions of a child with a peripheral neuropathy are important. In addition, there must be recognition of the child with a rapidly progressive neuropathy where a life-threatening condition is present, and urgent referral to a tertiary setting made wherever possible.

Flexor digitorum superficialis opposition tendon transfer improves hand function in children with Charcot-Marie-Tooth disease: case series

Charcot-Marie-Tooth disease limits hand function. Tendon transfer has not been reported in pediatric CMT. We report two severely affected children following long finger flexor digitorum superficialis opposition tendon transfer. Improvement was noted in palmar abduction, (30°/40°), opposition, (thumb to all digits), and acquisition of pincer, palmar, and lateral pinch with measureable force (1 lb). Dexterity testing improved on the 9 Hole Peg Test (1.03 s/77 s, 22 s) and Functional Dexterity Test (13 s/33 s, 88 s). Functional improvements were observed in self feeding, clothing management, and play. These cases support flexor digitorum superficialis opposition tendon transfer surgery to improve hand function in children with CMT.