Peripheral Myelin Protein 22 Gene Mutations in Charcot-Marie-Tooth Disease Type 1E Patients

The Link Between Paraquat and Demyelination: A Review of Current Evidence

Paraquat (1,1'-dimethyl-4,4'-bipyridilium dichloride), a widely used bipyridinium herbicide, is known for inducing oxidative stress, leading to extensive cellular toxicity, particularly in the lungs, liver, kidneys, and central nervous system (CNS), and is implicated in fatal poisonings. Due to its biochemical similarities with the neurotoxin 1-methyl-4-phenylpyridinium (MPP+), paraquat has been used as a Parkinson's disease model, although its broader neurotoxic effects suggest the participation of multiple mechanisms. Demyelinating diseases are conditions characterized by damage to the myelin sheath of neurons. They affect the CNS and peripheral nervous system (PNS), resulting in diverse clinical manifestations. In recent years, growing concerns have emerged about the impact of chronic, low-level exposure to herbicides on human health, particularly due to agricultural runoff contaminating drinking water sources and their presence in food. Studies indicate that paraquat may significantly impact myelinating cells, myelin-related gene expression, myelin structure, and cause neuroinflammation, potentially contributing to demyelination. Therefore, demyelination may represent another mechanism of neurotoxicity associated with paraquat, which requires further investigation. This manuscript reviews the potential association between paraquat and demyelination. Understanding this link is crucial for enhancing strategies to minimize exposure and preserve public health.

Clinical practice guidelines for the diagnosis and management of Charcot-Marie-Tooth disease

INTRODUCTION

Charcot-Marie-Tooth (CMT) disease is classified considering the neurophysiological and histological findings, the inheritance pattern and the underlying genetic defect. In recent years, with the advent of next generation sequencing, genetic complexity has increased exponentially, expanding the knowledge about disease pathways, and having an impact in clinical management. The aim of this guide is to offer recommendations for the diagnosis, prognosis, monitoring and treatment of this disease in Spain.

MATERIAL AND METHODS

This consensus guideline has been developed by a multidisciplinary panel encompassing a broad group of professionals including neurologists, neuropediatricians, geneticists, rehabilitators, and orthopaedic surgeons.

RECOMMENDATIONS

The diagnosis is based in the clinical characterization, usually presenting with a common phenotype. It should be followed by an appropriate neurophysiological study that allows for a correct classification, specific recommendations are established for the parameters that should be included. Genetic diagnosis must be approached in sequentially, once the PMP22 duplication has been ruled out if appropriate, a next generation sequencing should be considered taking into account the limitations of the available techniques. To date, there is no pharmacological treatment that modifies the course of the disease, but symptomatic management is important, as are the rehabilitation and orthopaedic considerations. The latter should be initiated early to identify and improve the patient's functional impairments, including individualised exercise guidelines, orthotic adaptation, and assessment of conservative surgeries such as tendon transpositions. The follow-up of patients with CMT is exclusively clinical, ancillary testing are not necessary in routine clinical practice.

Clinical, neurophysiological evaluation and genetic features of axonal Charcot-Marie-Tooth disease in a Chinese family

Charcot-Marie-Tooth disease (CMT) is a group of inherited peripheral neuropathies related to variants in the mitochondrial transfer RNA (mt-tRNAval) gene. Here, we report a Chinese family harboring the m.1661A>G variant in the mt-tRNAval gene. Clinical evaluation, neuroelectrodiagnostic testing, and nerve biopsy were performed on four affected family members. Weakness, spasms, and pain in the limbs (especially in the lower limbs) were the main complaints of the proband. Physical examination revealed atrophy and weakness in the distal limbs, increased muscle tone, and hyperreflexia in four limbs. Neuroelectrodiagnostic tests and nerve biopsy supported an axonal polyneuropathy. This study furthers the understanding of phenotype diversity caused by variants in the mt-tRNAval gene in CMT.

Clinical practice and outcomes of preimplantation genetic testing for CMT1A using a novel direct detection method

Background

Charcot-Marie-Tooth type 1A (CMT1A), the most frequent type of Charcot-Marie-Tooth disease, is mainly caused by a 1.4-Mb duplication containing the PMP22 gene. There is no effective treatment other than general supportive care and symptomatic treatment. Preimplantation genetic testing for monogenic defects (PGT-M) is an alternative approach for obtaining healthy babies.

Methods

A new technology and analysis method based on next-generation sequencing (NGS) was developed to detect duplication mutations directly. Simultaneously, aneuploidy and linkage analyses were performed to achieve a comprehensive and accurate embryo diagnosis.

Results

Eight couples were recruited in this study; PMP22 duplication was validated in seven couples, and PMP22 splicing mutation was found in one. Forty-five embryos from 12 PGT cycles were successfully detected using this novel method. The direct detection results for all embryos were consistent with the linkage analyses, suggesting a 100 % accuracy rate, and the aneuploidy rate of the biopsied blastocysts was 33.3 %. Eventually, 18 of the 45 diagnosed embryos were deemed suitable for transfer. Four healthy babies from three families were delivered and their genetic status confirmed by amniocentesis. Additionally, there were no adverse effects of anesthesia or increased pregnancy complications during PGT-M in female patients with CMT1A.

Conclusions

This study provided a simple, reliable, and efficient method that can directly detect PMP22 mutations based on NGS data and does not require positive family members. A clinical workflow for CMT1A interruption in the offspring before embryo implantation is also summarized.

Special Issue "Genetics and Epigenetics of Neuromuscular Diseases"

Neuromuscular disorders (NMDs) include several hereditary or acquired conditions that impair the neuromuscular system and muscle function [...].

INF2 mutations in patients with a broad phenotypic spectrum of Charcot-Marie-Tooth disease and focal segmental glomerulosclerosis

Mutations in INF2 are associated with the complex symptoms of Charcot-Marie-Tooth disease (CMT) and focal segmental glomerulosclerosis (FSGS). To date, more than 100 and 30 genes have been reported to cause these disorders, respectively. This study aimed to identify INF2 mutations in Korean patients with CMT. This study was conducted with 743 Korean families with CMT who were negative for PMP22 duplication. In addition, a family with FSGS was included in this study. INF2 mutations were screened using whole exome sequencing (WES) and filtering processes. As the results, four pathogenic INF2 mutations were identified in families with different clinical phenotypes: p.L78P and p.L132P in families with symptoms of both CMT and FSGS; p.C104Y in a family with CMT; and p.R218Q in a family with FSGS. Moreover, different CMT types were observed in families with CMT symptoms: CMT1 in two families and Int-CMT in another family. Hearing loss was observed in two families with CMT1. Pathogenicity was predicted by in silico analyses, and considerable conformational changes were predicted in the mutant proteins. Two mutations (p.L78P and p.C104Y) were unreported, and three families showed de novo mutations that were putatively occurred from fathers. This study suggests that patients with INF2 mutations show a broad phenotypic spectrum: CMT1, CMT1 + FSGS, CMTDIE + FSGS, and FSGS. Therefore, the genotype-phenotype correlation may be more complex than previously recognized. We believe that this study expands the clinical spectrum of patients with INF2 mutations and will be helpful in the molecular diagnosis of CMT and FSGS.