Yield of next-generation neuropathy gene panels in axonal neuropathies

Association of common genetic variants with chronic axonal polyneuropathy in the general population: a genome-wide association study

Introduction

Disease susceptibility of chronic axonal polyneuropathy is not fully explained by clinical risk factors. Therefore, we determined the contribution of common genetic variants in chronic axonal polyneuropathy in the general population.

Methods

This study was performed in two population-based studies. Polyneuropathy diagnosis was based on screening in the Rotterdam Study and on ICD-10 codes in the UK Biobank. We determined the heritability of the sural nerve amplitude and performed genome-wide association studies of chronic axonal polyneuropathy and sural sensory nerve amplitude. Furthermore, we zoomed in on variants in and surrounding 100 autosomal genes known to cause polyneuropathy based on literature and expert knowledge (candidate genes), and we performed a gene-based analysis. Analyses were adjusted for age, sex and population stratification.

Results

Chronic axonal polyneuropathy was present in 2,357 of the 458,567 participants and 54.3% of the total population was female. Heritability of sural nerve amplitude was 0.49 (p = 0.067) (N = 1,153). No variants (p < 5.0×10−8) or genes (p < 2.7×10−6) reached genome-wide significance for its association with polyneuropathy. Focusing on variants in and surrounding the candidate genes in the GWAS (p < 3.9×10−6) and on these genes in the gene-based analysis (p < 5.0×10−4) neither yielded significant results.

Discussion

We did not find common variants associated with chronic axonal polyneuropathy in the general population. Larger studies are needed to determine if genetic susceptibility based on both common and rare genetic variants affect the risk for chronic axonal polyneuropathy in the general population.

Genetic testing in adults with neurologic disorders: indications, approach, and clinical impacts

The role of genetic testing in neurologic clinical practice has increased dramatically in recent years, driven by research on genetic causes of neurologic disease and increased availability of genetic sequencing technology. Genetic testing is now indicated for adults with a wide range of common neurologic conditions. The potential clinical impacts of a genetic diagnosis are also rapidly expanding, with a growing list of gene-specific treatments and clinical trials, in addition to important implications for prognosis, surveillance, family planning, and diagnostic closure. The goals of this review are to provide practical guidance for clinicians about the role of genetics in their practice and to provide the neuroscience research community with a broad survey of current progress in this field. We aim to answer three questions for the neurologist in practice: Which of my patients need genetic testing? What testing should I order? And how will genetic testing help my patient? We focus on common neurologic disorders and presentations to the neurology clinic. For each condition, we review the most current guidelines and evidence regarding indications for genetic testing, expected diagnostic yield, and recommended testing approach. We also focus on clinical impacts of genetic diagnoses, highlighting a number of gene-specific therapies recently approved for clinical use, and a rapidly expanding landscape of gene-specific clinical trials, many using novel nucleotide-based therapeutic modalities like antisense oligonucleotides and gene transfer. We anticipate that more widespread use of genetic testing will help advance therapeutic development and improve the care, and outcomes, of patients with neurologic conditions.

Using gene panels in the diagnosis of neuromuscular disorders: A mini-review

The diagnosis of inherited neuromuscular disorders is challenging due to their genetic and phenotypic variability. Traditionally, neurophysiology and histopathology were primarily used in the initial diagnostic approach to these conditions. Sanger sequencing for molecular diagnosis was less frequently utilized as its application was a time-consuming and cost-intensive process. The advent and accessibility of next-generation sequencing (NGS) has revolutionized the evaluation process of genetically heterogenous neuromuscular disorders. Current NGS diagnostic testing approaches include gene panels, whole exome sequencing (WES), and whole genome sequencing (WGS). Gene panels are often the most widely used, being more accessible due to availability and affordability. In this mini-review, we describe the benefits and risks of clinical genetic testing. We also discuss the utility, benefits, challenges, and limitations of using gene panels in the evaluation of neuromuscular disorders.

Genetic Workup for Charcot–Marie–Tooth Neuropathy: A Retrospective Single-Site Experience Covering 15 Years

Charcot–Marie–Tooth (CMT) disease is the most commonly inherited neurological disorder. This study includes patients affected by CMT during regular follow-ups at the CMT clinic in Genova, a neuromuscular university center in the northwest of Italy, with the aim of describing the genetic distribution of CMT subtypes in our cohort and reporting a peculiar phenotype. Since 2004, 585 patients (447 index cases) have been evaluated at our center, 64.9% of whom have a demyelinating neuropathy and 35.1% of whom have an axonal neuropathy. A genetic diagnosis was achieved in 66% of all patients, with the following distribution: CMT1A (48%), HNPP (14%), CMT1X (13%), CMT2A (5%), and P0-related neuropathies (7%), accounting all together for 87% of all the molecularly defined neuropathies. Interestingly, we observe a peculiar phenotype with initial exclusive lower limb involvement as well as lower limb involvement that is maintained over time, which we have defined as a “strictly length-dependent” phenotype. Most patients with this clinical presentation shared variants in either HSPB1 or MPZ genes. The identification of distinctive phenotypes such as this one may help to address genetic diagnosis. In conclusion, we describe our diagnostic experiences as a multidisciplinary outpatient clinic, combining a gene-by-gene approach or targeted gene panels based on clinical presentation.

Diagnostic yield of advanced genetic testing in patients with hereditary neuropathies: A retrospective single-site study

INTRODUCTION/AIMS

Advanced genetic testing including next-generation sequencing (AGT/NGS) has facilitated DNA testing in the clinical setting and greatly expanded new gene discovery for the Charcot-Marie-Tooth neuropathies and other hereditary neuropathies (CMT/HN). Herein, we report AGT/NGS results, clinical findings, and diagnostic yield in a cohort of CMT/HN patients evaluated at our neuropathy care center.

METHODS

We reviewed the medical records of all patients with suspected CMT/HN who underwent AGT/NGS at the Hospital for Special Care from January 2017 through January 2020. Patients with variants reported as pathogenic or likely pathogenic were included for further clinical review.

RESULTS

We ordered AGT/NGS on 108 patients with suspected CMT/HN. Of these, pathogenic or likely pathogenic variants were identified in 17 patients (diagnostic yield, 15.7%), including 6 (35%) with PMP22 duplications; 3 (18%) with MPZ variants; 2 (12%) with MFN2 variants; and 1 each with NEFL, IGHMBP2, GJB1, BSCL2, DNM2, and TTR variants. Diagnostic yield increased to 31.0% for patients with a positive family history.

DISCUSSION

AGT/NGS panels can provide specific genetic diagnoses for a subset of patients with CMT/HN disorders, which improves disease and genetic counseling and prepares patients for disease-focused therapies. Despite these advancements, many patients with known or suspected CMT/HN disorders remain without a specific genetic diagnosis. Continued advancements in genetic testing, such as multiomic technology and better understanding of genotype-phenotype correlation, will further improve detection rates for patients with suspected CMT/HN disorders.

Charcot-Marie-Tooth disease and hereditary motor neuropathies – Update 2020

Inherited peripheral neuropathy is the most common hereditary neuromuscular disease with a prevalence of about 1:2,500. The most frequent form is Charcot-Marie-Tooth disease (CMT, or hereditary motor and sensory neuropathy [HMSN]). Other clinical entities are hereditary neuropathy with liability to pressure palsies (HNPP), distal hereditary motor neuropathies (dHMN), and hereditary sensory and autonomic neuropathies (HSAN). With the exception of HNPP, which is almost always caused by defects of the PMP22 gene, all other forms show genetic heterogeneity with altogether more than 100 genes involved. Mutation detection rates vary considerably, reaching up to 80 % in demyelinating CMT (CMT1) but are still as low as 10–30 % in axonal CMT (CMT2), dHMN, and HSAN. Based on current information, analysis of only four genes (PMP22, GJB1, MPZ, MFN2) identifies 80–90 % of CMT-causing mutations that can be detected in all known disease genes. For the remaining patients, parallel analysis of multiple neuropathy genes using next-generation sequencing is now replacing phenotype-oriented multistep gene-by-gene sequencing. Such approaches tend to generate a wealth of genetic information that requires comprehensive evaluation of the pathogenic relevance of identified variants. In this review, we present current classification systems, specific phenotypic clues, and diagnostic yields in the different subgroups of hereditary CMT and motor neuropathies.

A novel HSPB1 mutation associated with a late onset CMT2 phenotype: Case presentation and systematic review of the literature

Mutations in the HSPB1 gene are associated with Charcot-Marie-Tooth (CMT) disease type 2F (CMT2F) and distal hereditary motor neuropathy type 2 (dHMN2). More than 18 pathogenic mutations spanning across the whole HSPB1 gene have been reported. Three family members with a novel p.P57S (c.169C>T) HSPB1 mutation resulting in a late onset axonal neuropathy with heterogeneous clinical and electrophysiological features are detailed. We systematically reviewed published case reports and case series on HSPB1 mutations. While a genotype-phenotype correlation was not obvious, we identified a common phenotype, which included adult onset, male predominance, motor more frequently than sensory involvement, distal and symmetric distribution with preferential involvement of plantar flexors, and a motor and axonal electrophysiological picture.