A novel GJB1 frameshift mutation produces a transient CNS symptom of X-linked Charcot-Marie-Tooth disease

Spatial Fluctuation of Central Nervous System Lesions in X-linked Charcot-Marie-Tooth Disease with a Novel GJB1 Mutation

X-linked Charcot-Marie-Tooth disease type 1 (CMTX1), the most common form of CMTX, is caused by gap-junction beta 1 (GJB1) mutations. We herein report a 25-year-old Japanese man with disorientation, right hemiparesis, and dysarthria. Brain magnetic resonance imaging (MRI) showed high signal intensities in the bilateral cerebral white matter on diffusion-weighted imaging. He had experienced 2 episodes of transient central nervous system symptoms (at 7 and 13 years old). A genetic analysis identified a novel GJB1 mutation, c.169C>T, p.Gln57*. MRI abnormalities shifted from the cerebral white matter to the corpus callosum and had disappeared at the five-month follow-up. Transient changes between these lesions may indicate CMTX1.

Review of general and head and neck/oral and maxillofacial features of Charcot-Marie-Tooth disease and dental management considerations

Charcot-Marie-Tooth disease (CMTD) is an uncommon progressive neuromuscular disorder of the peripheral nervous system and primarily leads to distal extremity weakness and sensory deficits. Frequently, affected patients manifest pes cavus, drop foot, and digit contractures that may pose significant challenges in ambulation and grasping objects. Although there are numerous articles of this syndrome in the medical literature, there is a limited number of dental publications. The objective of this article is to review the general and head and neck/oral and maxillofacial features of CMTD. General guidelines for dental management are also provided.

CIDP mimics: a case series

Background

To report our experience with a group of patients referred for refractory CIDP who fulfilled “definite” electrodiagnostic EFNS criteria for CIDP but were found to have an alternate diagnosis.

Methods

Patients who were seen between 2017 and 2019 for refractory CIDP that fulfilled “definite” electrodiagnostic ENFS criteria for CIDP, but had an alternate diagnosis, were included. Patients who correctly had CIDP, anti MAG neuropathy, or MMN with conduction block, were excluded from the study. Demographics, clinical and electrophysiological characteristics, pertinent workup, final alternate diagnoses, and outcomes were collected.

Results

Seven patients were included: POEMS (n = 5), CANOMAD (n = 1), and neurolymphomatosis (n = 1). Most patients reported neuropathic pain and leg swelling (n = 6) or significant weight loss (n = 4). All patients had a monoclonal protein, and most patients who were tested had an elevated VEGF and CSF cyto-albuminologic dissociation. Electrophysiology showed pronounced intermediate more than distal demyelination, and axonal loss in the lower extremities. Response to steroids or IVIG varied, but some patients did respond to these treatments, especially early in the disease.

Conclusion

Pain, systemic symptoms, suggestive electrophysiological findings, and/or a serum monoclonal protein should raise suspicion for CIDP mimics. Initial response to steroids or IVIG, over reliance on CSF, and electrophysiology findings can all be misleading.

New evidence for secondary axonal degeneration in demyelinating neuropathies

Development of peripheral nervous system (PNS) myelin involves a coordinated series of events between growing axons and the Schwann cell (SC) progenitors that will eventually ensheath them. Myelin sheaths have evolved out of necessity to maintain rapid impulse propagation while accounting for body space constraints. However, myelinating SCs perform additional critical functions that are required to preserve axonal integrity including mitigating energy consumption by establishing the nodal architecture, regulating axon caliber by organizing axonal cytoskeleton networks, providing trophic and potentially metabolic support, possibly supplying genetic translation materials and protecting axons from toxic insults. The intermediate steps between the loss of these functions and the initiation of axon degeneration are unknown but the importance of these processes provides insightful clues. Prevalent demyelinating diseases of the PNS include the inherited neuropathies Charcot-Marie-Tooth Disease, Type 1 (CMT1) and Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) and the inflammatory diseases Acute Inflammatory Demyelinating Polyneuropathy (AIDP) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Secondary axon degeneration is a common feature of demyelinating neuropathies and this process is often correlated with clinical deficits and long-lasting disability in patients. There is abundant electrophysiological and histological evidence for secondary axon degeneration in patients and rodent models of PNS demyelinating diseases. Fully understanding the involvement of secondary axon degeneration in these diseases is essential for expanding our knowledge of disease pathogenesis and prognosis, which will be essential for developing novel therapeutic strategies.

Systematic review of CMTX1 patients with episodic neurological dysfunction

OBJECTIVE

X-linked Charcot-Marie-Tooth type 1 (CMTX1) is an inherited peripheral neuropathy caused by mutations in the gap junction beta 1 (GJB1) gene, which encodes the connexin32 protein. A small number of patients with GJB1 mutations present with episodic neurological dysfunction and reversible white matter lesions, which has not been adequately reported. Here, we aim to enable clinicians to further understand this particular situation through systematically reviewing all published relevant cases.

METHODS

We conducted a comprehensive search of the PubMed electronic database for medical literature relevant to CMTX1 patients with episodic neurological dysfunction and then fully analyzed the general information, clinical manifestations, and characteristics of magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) analysis, and nerve conduction study (NCS).

RESULTS

We identified 47 cases of CMTX1 associated with episodic central nervous system (CNS) dysfunction from 38 publications. CMTX1 patients experienced episodic CNS deficits at a young age, ranging from infancy to 26 years, and 45 (95.7%) of them were male. The CNS symptoms manifested as facial, lingual, or limb weakness in 44 (93.6%), dysarthria or dysphagia in 39 (83.0%), facial or limb numbness in 15 (31.9%), and ataxia in 10 (21.3%) patients. The duration of episodic symptoms ranged from 3 minutes to 6 months. Thirty (63.8%) CMTX1 cases have reported obvious predisposing factors, among which the most common factors were infection or fever (27.7%), travel to high altitude (12.8%), and intensive exercise (8.5%). As for brain MRI, most abnormal signals were found in bilateral deep white matter (88.9%) and corpus callosum (80.0%). In addition, most of the NCS results were abnormal, including prolonged latency, reduced amplitude, and slowed conduction velocity. The motor nerve conduction velocity (MNCV) of median nerve was the most detectable and valuable, ranging from 25 to 45 m/s.

INTERPRETATION

We have reported the most comprehensive summary of the demographic and clinical profile from 47 CMTX1 patients with episodic CNS deficits and provided new insight into the phenotype spectrum of CMTX1. We hope that our study can help clinicians make early diagnosis and implement the best prevention and treatment strategies for CMTX1 patients with episodic CNS deficits.

A novel GJB1 mutation associated with X-linked Charcot-Marie-Tooth disease in a large Chinese family pedigree

BACKGROUND

Charcot-Marie-Tooth (CMT) disease is a group of hereditary neuropathies with high phenotypic and genetic heterogeneity. In this study, we report a large family with X-linked CMT (CMTX) caused by a novel GJB1 mutation.

METHODS

A family with the clinical diagnosis of CMTX was investigated. For mutation analysis, the coding region of GJB1 was sequenced using DNA from 15 family members. The identified GJB1 mutation was investigated by DHPLC in 120 normal controls. Mutation reanalysis was performed based on whole-exome sequencing (WES). Cell transfection studies were performed to characterize the function of the novel mutation.

RESULTS

A missense mutation (c.605T>A) in GJB1 was detected in five patients and eight female carriers but not in two unaffected members of the family. The mutation was not found in 120 healthy controls and has not been previously reported. WES excluded other pathogenic mutations in the family. The pathogenicity of the mutation was confirmed by disrupting the membrane localization of the encoded proteins.

CONCLUSION

Our findings demonstrate that a novel mutation (c.605T>A) in GJB1 is associated with CMTX and adds to the repertoire of GJB1 mutations related to CMTX.

Chaperoning Endoplasmic Reticulum-Associated Degradation (ERAD) and Protein Conformational Diseases

Misfolded proteins compromise cellular homeostasis. This is especially problematic in the endoplasmic reticulum (ER), which is a high-capacity protein-folding compartment and whose function requires stringent protein quality-control systems. Multiprotein complexes in the ER are able to identify, remove, ubiquitinate, and deliver misfolded proteins to the 26S proteasome for degradation in the cytosol, and these events are collectively termed ER-associated degradation, or ERAD. Several steps in the ERAD pathway are facilitated by molecular chaperone networks, and the importance of ERAD is highlighted by the fact that this pathway is linked to numerous protein conformational diseases. In this review, we discuss the factors that constitute the ERAD machinery and detail how each step in the pathway occurs. We then highlight the underlying pathophysiology of protein conformational diseases associated with ERAD.

Genetic and phenotypic profile of 112 patients with X-linked Charcot-Marie-Tooth disease type 1

BACKGROUND AND PURPOSE

X-linked Charcot-Marie-Tooth disease type 1 (CMTX1), caused by mutations in gap junction protein beta 1 (GJB1), is characterized by various central nervous system symptoms and gender differences of clinical severity. The aim of this study was to identify the frequency and mutation spectrum of CMTX1 patients in Japan and to demonstrate their phenotypic diversities.

METHODS

Using three high-throughput sequencing systems, targeted gene panel sequencing on 1483 unrelated index patients with suspected Charcot-Marie-Tooth (CMT) disease was performed. The peripheral and central nervous system involvements of all patients with GJB1 variants were assessed retrospectively and a detailed gender comparison was conducted with the CMT examination score.

RESULTS

Twenty-three novel and 36 described GJB1 variants were identified from 88 pedigrees, in which 34 female and 78 male patients were enrolled. Mean age at onset of the male patients was much younger than the females, 21.56 ± 17.63 years vs. 35.53 ± 23.72 years (P = 0.007). Male patients presented with more severe phenotypes in every examination item, but statistical differences were observed only in motor dysfunctions of the lower extremities and vibration sensation. No significant sensory difference was identified between genders, either clinically or electrophysiologically. Central nervous system dysfunctions were found in 15 patients from 12 pedigrees. Therein, six patients developed stroke-like phenotypes, with dysarthria as the leading symptom.

CONCLUSIONS

A relatively lower frequency of CMTX1 (5.9%) was demonstrated and a broad mutation spectrum of GJB1 was described. Detailed clinical differences between genders and various central nervous system symptoms were also illustrated, even in the same pedigree.

[Charcot-Marie-Tooth disease showing transient central nervous system lesions after a large amount of alcohol intake: A case report]

A 23-year-old man experienced numbness in the perioral region and right arm, and right leg weakness on the second day after drinking a large amount of alcohol during foreign travel. His symptoms disappeared but then reappeared repetitively. Cerebral MRI performed on the third day after onset showed multiple white matter lesions; however, these lesions disappeared 26 days after onset. Neurological examination and nerve conduction studies revealed demyelinating polyneuropathy. Genetic testing for Charcot-Marie-Tooth disease, X-linked dominant 1 (CMTX1) due to GJB1 mutation was conducted based on the symptoms of transient central nervous system lesions and polyneuropathy exhibited by the patient and his mother. As a result, a c.530T>C (p.V177A) substitution in exon 2 of GJB1 was identified. CMTX1 patients should be advised to avoid excessive drinking because this could induce central nervous system lesions.

The Electrophysiological Features in X-Linked Charcot-Marie-Tooth Disease With Transient Central Nervous System Deficits

Background: Electrophysiological examination plays an important role in the diagnosis of X-linked Charcot-Marie-Tooth disease (CMTX1) with transient central nervous system deficits. However, the electrophysiological features are seldom reported.

Methods: We reviewed and analyzed published reports to determine the electrophysiological features of CMTX1 patients with transient central nervous system deficits.

Results: A total of 21 CMTX1 patients with transient central nervous system deficits were found in 17 published case reports/series. The age of onset ranged from 0.5 to 18 years (mean 12.02 ± 0.78 years). All patients were male. Recurrent episodes of central nervous system deficits were reported in all 21 cases and resolved in periods ranging from several minutes to 3 days. All 20 patients who had MRIs at presentation had bilaterally symmetrical abnormal T2/Diffusion signals in the white matter without enhancement of gadolinium. All subsequent MRIs showed improvement or were within normal limits. The median motor nerve conduction velocity (MNCV), motor latencies, and compound muscle action potential (CMAP) amplitude were the most commonly measurable electrophysiological parameters (85.7%). All cases that had MNCV at presentation had slower and significantly decreased MNCV compared with the normal value (34.1 ± 1.10 m/s vs. 46.8±2.05 m/s, P < 0.0001; 95% CI, −17.4 to −7.92). The average variations of MNCV in median nerve, ulnar nerve, peroneal nerve, and tibial nerve were 22.0 ± 5.96%, 27.6 ± 11.9%, 25.9 ± 4.36%, and 27.3 ± 4.30%, respectively. All cases with measured sensory nerve conduction velocity (SNCV) at presentation had slower and significantly decreased SNCV compared with the normal value (35.3 ± 1.33 m/s vs. 47.7 ± 2.40 m/s, P < 0.001; 95% CI −18.2 to −6.46). The average variations of SNCV in median nerve, ulnar nerve, and sural nerve were 19.9 ± 8.24%, 25.2 ± 7.75%, and 23.2 ± 3.95%, respectively.

Conclusion: This case series serves as a reminder that electrophysiological examination should be included in the diagnosis of recurrent and episodic neurological deficit with white matter lesions. Median MNCV is a sensitive and valuable parameter to support the diagnosis of CMTX1 with transient central nervous system deficits.

Hereditary and inflammatory neuropathies: a review of reported associations, mimics and misdiagnoses

Distinguishing between hereditary and inflammatory neuropathy is usually straightforward on clinical grounds with the help of a family history. There are nevertheless cases where the distinction is less clear. The advent of molecular genetics has in the past several years aided confirmatory diagnosis for an increasing proportion of patients with genetic neuropathy. Various reports have described associations of Charcot-Marie-Tooth disease with a suspected or confirmed inflammatory neuropathy occasionally responding to immunotherapy. Possible predisposition to an inflammatory component was suggested in a subset of patients. Such reports have, however, been relatively few in number, suggesting the rarity of such associations and of such a predisposition if it exists. There have been a number of publications detailing clinical presentations suggestive of inflammatory neuropathy in patients with a known or later proven genetic aetiology, and subsequently felt to be part of the phenotype rather than representing an association. A number of genetically mediated multisystemic diseases with neuropathy have otherwise been reported as mimicking chronic inflammatory demyelinating polyneuropathy (CIDP). The most common example is that of familial amyloid polyneuropathy, of particular concern for the clinician when misdiagnosed as CIDP, in view of the therapeutic implications. We review the literature on reported associations, mimics and misdiagnoses of hereditary and inflammatory neuropathy and attempt to determine a practical approach to the problem in clinical practice using clinical features, electrophysiology, histopathology and targeted early genetic testing. The issue of attempting immunomodulatory therapy is discussed in view of the published literature.

CNS involvement in CMTX1 caused by a novel connexin 32 mutation: a 6-year follow-up in neuroimaging and nerve conduction

X-linked Charcot-Marie-Tooth disease, type 1 (CMTX1) is one of the most common inherited neurological disorders. Obvious CNS involvement is relatively rare in CMTX1 patients. A 24-year-old male with CMTX1 presented with three transient stroke-like attacks, and was followed up regularly for 6 years with brain MRI and electrophysiological examination. Transient symmetrical high signals on T2 imaging and restricted diffusion were found in bilateral deep white matter. Electrophysiological measurement revealed a sensorimotor peripheral neuropathy with slightly reduced nerve conduction velocities. A novel thymine to cytosine mutation at nucleotide position 445 in the connexin 32 allele of the GJB1 gene was identified. During the 6-year longitudinal study, patient's motor and sensory function did not worsen; radiological abnormalities correlated with episodes of CNS dysfunction and resolved after clinical recovery; electrophysiological records showed no obvious change. Little change in the patient's clinical, radiological and electrophysiological results over the follow-up reflected a slow disease progression.

A Review of X-linked Charcot-Marie-Tooth Disease

X-linked Charcot-Marie-Tooth disease (CMTX) is the second common genetic variant of CMT. CMTX type 1 causes 90% of CMTX. The most important clinical features of CMTX are similar with other types of CMT; however, a few patients get the central nervous system involved with or without white matter lesions; males are more severely and earlier affected than females. In this review, the authors focus on the origin and classification of CMTX, the central nervous system manifestations of CMTX1, the possible mechanism by which GJB1 mutations cause CMT1X, and the emerging therapeutic strategies for CMTX. Moreover, several cases are presented to illustrate the central nervous system manifestations.

Degradation of a connexin40 mutant linked to atrial fibrillation is accelerated

Several Cx40 mutants have been identified in patients with atrial fibrillation (AF). We have been working to identify physiological or cell biological abnormalities of several of these human mutants that might explain how they contribute to disease pathogenesis. Wild type (wt) Cx40 or four different mutants (P88S, G38D, V85I, and L229M) were expressed by the transfection of communication-deficient HeLa cells or HL-1 cardiomyocytes. Biophysical channel properties and the sub-cellular localization and protein levels of Cx40 were characterized. Wild type Cx40 and all mutants except P88S formed gap junction plaques and induced significant gap junctional conductances. The functional mutants showed only modest alterations of single channel conductances or gating by trans-junctional voltage as compared to wtCx40. However, immunoblotting indicated that the steady state levels of G38D, V85I, and L229M were reduced relative to wtCx40; most strikingly, G38D was only 20-31% of wild type levels. After the inhibition of protein synthesis with cycloheximide, G38D (and to a lesser extent the other mutants) disappeared much faster than wtCx40. Treatment with the proteasomal inhibitor, epoxomicin, greatly increased levels of G38D and restored the abundance of gap junctions and the extent of intercellular dye transfer. Thus, G38D, V85I, and L229M are functional mutants of Cx40 with small alterations of physiological properties, but accelerated degradation by the proteasome. These findings suggest a novel mechanism (protein instability) for the pathogenesis of AF due to a connexin mutation and a novel approach to therapy (protease inhibition).

The central nervous system phenotype of X-linked Charcot-Marie-Tooth disease: a transient disorder of children and young adults

We describe 2 patients with X-linked Charcot-Marie-Tooth disease, type 1 (CMTX1) disease and central nervous system manifestations and review 19 cases from the literature. Our first case had not been previously diagnosed with Charcot-Marie-Tooth disease, and the second case, although known to have Charcot-Marie-Tooth disease, was suspected of having CMTX1 after presentation with central nervous system manifestations. The most common central nervous system manifestations were transient and included dysarthria, ataxia, hemiparesis, and tetraparesis resembling periodic paralysis. Of the 21 patients, 19 presented at 21 years of age or younger, implicating CMTX1 with transient central nervous system manifestations as a disorder that predominantly affects children and adolescents. CMTX1 should be included in the differential diagnosis of patients who present with transient central nervous system phenomena, including stroke-like episodes, tetraparesis suggestive of periodic paralysis, dysarthria, ataxia, or combinations of these deficits. Reversible, bilateral, nonenhancing white matter lesions and restricted diffusion on magnetic resonance imaging are characteristic features of the central nervous system phenotype of CMTX1.

A family with IVIg-responsive Charcot-Marie-Tooth disease

We report a family of intravenous immunoglobulin (IVIg)-responsive X-linked Charcot-Marie-Tooth disease Type 1 (CMT1X) with a novel gap junction protein 1 mutation. Two of three siblings in the family complained of subacute motor and sensory impairment, and their symptoms improved after the administration of IVIg. Additional IVIg treatment also resulted in similar improvement. The other also showed a mild improvement on IVIg. It has been suggested that an immune-mediated process is involved in the progression of neuropathy in CMT1X. The finding in our report provides evidence of susceptibility to immune-mediated demyelinating neuropathy in some form of CMT1X. Superimposed demyelinating neuropathy as well as a gradual deterioration of neuropathy over decades can be a clinical manifestation of CMT1X.

The delicate balance between secreted protein folding and endoplasmic reticulum-associated degradation in human physiology

Protein folding is a complex, error-prone process that often results in an irreparable protein by-product. These by-products can be recognized by cellular quality control machineries and targeted for proteasome-dependent degradation. The folding of proteins in the secretory pathway adds another layer to the protein folding "problem," as the endoplasmic reticulum maintains a unique chemical environment within the cell. In fact, a growing number of diseases are attributed to defects in secretory protein folding, and many of these by-products are targeted for a process known as endoplasmic reticulum-associated degradation (ERAD). Since its discovery, research on the mechanisms underlying the ERAD pathway has provided new insights into how ERAD contributes to human health during both normal and diseases states. Links between ERAD and disease are evidenced from the loss of protein function as a result of degradation, chronic cellular stress when ERAD fails to keep up with misfolded protein production, and the ability of some pathogens to coopt the ERAD pathway. The growing number of ERAD substrates has also illuminated the differences in the machineries used to recognize and degrade a vast array of potential clients for this pathway. Despite all that is known about ERAD, many questions remain, and new paradigms will likely emerge. Clearly, the key to successful disease treatment lies within defining the molecular details of the ERAD pathway and in understanding how this conserved pathway selects and degrades an innumerable cast of substrates.