Mutational analysis of PMP22, GJB1 and MPZ in Greek Charcot-Marie-Tooth type 1 neuropathy patients

A study concept of expeditious clinical enrollment for genetic modifier studies in Charcot-Marie-Tooth neuropathy 1A

BACKGROUND

Caused by duplications of the gene encoding peripheral myelin protein 22 (PMP22), Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common hereditary neuropathy. Despite this shared genetic origin, there is considerable variability in clinical severity. It is hypothesized that genetic modifiers contribute to this heterogeneity, the identification of which may reveal novel therapeutic targets. In this study, we present a comprehensive analysis of clinical examination results from 1564 CMT1A patients sourced from a prospective natural history study conducted by the RDCRN-INC (Inherited Neuropathy Consortium). Our primary objective is to delineate extreme phenotype profiles (mild and severe) within this patient cohort, thereby enhancing our ability to detect genetic modifiers with large effects.

METHODS

We have conducted large-scale statistical analyses of the RDCRN-INC database to characterize CMT1A severity across multiple metrics.

RESULTS

We defined patients below the 10th (mild) and above the 90th (severe) percentiles of age-normalized disease severity based on the CMT Examination Score V2 and foot dorsiflexion strength (MRC scale). Based on extreme phenotype categories, we defined a statistically justified recruitment strategy, which we propose to use in future modifier studies.

INTERPRETATION

Leveraging whole genome sequencing with base pair resolution, a future genetic modifier evaluation will include single nucleotide association, gene burden tests, and structural variant analysis. The present work not only provides insight into the severity and course of CMT1A, but also elucidates the statistical foundation and practical considerations for a cost-efficient and straightforward patient enrollment strategy that we intend to conduct on additional patients recruited globally.

An Elderly Woman with Complaints of Pain and Hearing Loss, Diagnosed with CMT1A with PMP22 Duplication

Charcot-Marie-Tooth (CMT) disease is a heterogeneous hereditary motor and sensory neuropathy of the peripheral nervous system, with CMT1A in particular being the most common form. We encountered a 76-year-old woman with CMT1A who had a history of pain attacks and hearing loss from a young age, with motor symptoms manifesting late in life. Her pain and hearing loss may have been related to CMT. Our case also raises the possibility that neuropathic pain and hearing loss may precede the classic motor symptoms of CMT1A.

Whole exome sequencing establishes diagnosis of Charcot-Marie-Tooth 4J, 1C, and X1 subtypes

BACKGROUND

Charcot-Marie-Tooth (CMT) hereditary polyneuropathies pose a diagnostic challenge. Our aim here is to describe CMT patients diagnosed by whole exome sequencing (WES) following years of fruitless testing.

METHODS/RESULTS

Three patients with polyneuropathy suspected to be genetic in origin, but not harboring PMP22 gene deletion/duplication, were offered WES. The first patient, a 66-year-old man, had been suffering from progressive weakness and atrophies in the lower and upper extremities for 20 years. Due to ambiguous electrophysiological findings, immune therapies were administered to no avail. Twelve years after PMP22 deletion/duplication testing, WES revealed two pathogenic variants in the FIG4 gene (p.Ile41Thr and p.Phe598fs, respectively), as a cause of CMT 4J. The second patient, a 19-year-old man, had been suffering from hearing and gait impairment since at least his infancy, and recently presented with weakness and dystonia of the lower extremities. In this patient, WES identified the p.Leu122Val LITAF gene variant in heterozygous state, suggesting the diagnosis of CMT 1C, several years after initial genetic analyses. The third patient, a 44-year-old man, presented with progressive weakness and atrophies of the lower and upper extremities since the age of 17 years old. In this patient, WES identified the hemizygous p.Arg164Gln pathogenic variant in the GJB1 gene, establishing the diagnosis of CMT X1, 8 years after testing for PMP22 deletion/duplication.

CONCLUSION

Novel diagnostic techniques, such as WES, offer the possibility to decipher the cause of CMT subtypes, ending the diagnostic Odyssey of the patients and sparing them from unnecessary and potentially harmful treatments.

Evidence for Cognitive Deficits in X-Linked Charcot-Marie-Tooth Disease

OBJECTIVE

X-linked Charcot-Marie-Tooth disease (CMTX) is an hereditary neuropathy caused by mutations in GJB1 coding for connexin-32, found in Schwann cells, but also expressed in oligodendrocytes. Reports have identified CNS involvement in CMTX, but no systematic study of cognitive function has been published.

METHODS

We assessed 24 CMTX patients (13 males; 9GJB1 mutations) with a comprehensive neuropsychological battery, including tests of memory, language, and executive functions.

RESULTS

No differences in cognitive performance were observed between males and females. A case-by-case investigation revealed selective deficits in individual patients. One subgroup (29%) demonstrated executive abnormalities; and a non-overlapping subgroup (29%), prominent reading (decoding) abnormalities.

CONCLUSIONS

The present data provide evidence for cognitive deficits in CMTX. Emerging neuropsychological patterns are also discussed.

A Computational Approach to Identify a Potential Alternative Drug With Its Positive Impact Toward PMP22

Mutations in the Peripheral Myelin Protein 22 (PMP22) leads to Charcot Marie Tooth type 1A (CMT1A, a subtype of CMT1) disease which is the most common inherited neuropathy of peripheral nervous system. In the present study, we used series of in silico prediction methods to screen and identify the most deleterious non-synonymous SNPs (nsSNPs) in PMP22 gene. Out of 48 nsSNPs, five nsSNPs (L16P, L19P, T23R, W28R, and L147R) associated with PMP22 were predicted to be highly deleterious and destabilizing the protein. To explore the possible structure-function relationship, we employed abinitio modeling strategy using the CABS-fold server to predict the three-dimensional structure models in the absence of crystallized structures in PMP22 protein. We used Cytoscape 3.4.0 plugin Integrated Complex Traits Networks interface (iCTNet) to identify the probable drug-gene interactions in PMP22 gene. A total of 22 chemical compounds yielded from the aforementioned tool was subjected to Molinspiration and OSIRIS program to screen and identify the potent drug molecules for further analysis. Five chemical compounds with excellent bioavailability and drug relevant property were selected for molecular docking simulation study. We modeled five mutant structures at their corresponding positions and performed molecular docking simulation analysis using AutoDock Tools (ADT) version 1.5.6 and ArgusLab 4.0.1 tools to analyze their interaction patterns and binding efficacy. Based on the results obtained from the computational study, we predict that estradiol could be a potential drug of choice for treating patients with CMT1A which needs larger attention from biologists in the near future. J. Cell. Biochem. 118: 3730-3743, 2017. © 2017 Wiley Periodicals, Inc.

Clinical and genetic spectra in a series of Chinese patients with Charcot-Marie-Tooth disease

The aim of this study was to determine the clinical features and frequencies of genetic subtypes in a series of patients with Charcot-Marie-Tooth (CMT) disease from Eastern China. Patients were divided into three subtypes, CMT1, CMT2 and hereditary neuropathy with liability to pressure palsy (HNPP), according to their electrophysiological manifestations. Multiplex ligation-dependent probe analysis (MLPA) was performed to detect duplications/deletions in the PMP22 gene. The coding regions and splice sites of the GJB1, MPZ, MFN2 and GDAP-1 genes were determined by direct sequencing. Among the 148 patients in the study, 37.2% of the cases had mutations in genes assessed. The mutation detection rate was higher in patients with family histories than in spontaneous cases. PMP22 duplication (13.5%) was predominant in this group of patients, followed by PMP22 deletion (11.5%), and point mutations in GJB1 (8.8%), MPZ (2.0%) and MFN2 (0.7%). Three novel mutations (c.151T>C and c.310 A>G in GJB1 and c.1516 C>G in MFN2) were detected. A small deletion in PMP22 exon 4 was detected in a patient with severe CMT1. Genetic tests have great value in CMT patients with family histories. The frequency of PMP22 duplications was lower in Asian patients than in others. We suggest that genetic testing strategies in CMT patients should be primarily based on electromyography data.

CMT subtypes and disease burden in patients enrolled in the Inherited Neuropathies Consortium natural history study: a cross-sectional analysis

BACKGROUND

The international Inherited Neuropathy Consortium (INC) was created with the goal of obtaining much needed natural history data for patients with Charcot-Marie-Tooth (CMT) disease. We analysed clinical and genetic data from patients in the INC to determine the distribution of CMT subtypes and the clinical impairment associated with them.

METHODS

We analysed data from 1652 patients evaluated at 13 INC centres. The distribution of CMT subtypes and pathogenic genetic mutations were determined. The disease burden of all the mutations was assessed by the CMT Neuropathy Score (CMTNS) and CMT Examination Score (CMTES).

RESULTS

997 of the 1652 patients (60.4%) received a genetic diagnosis. The most common CMT subtypes were CMT1A/PMP22 duplication, CMT1X/GJB1 mutation, CMT2A/MFN2 mutation, CMT1B/MPZ mutation, and hereditary neuropathy with liability to pressure palsy/PMP22 deletion. These five subtypes of CMT accounted for 89.2% of all genetically confirmed mutations. Mean CMTNS for some but not all subtypes were similar to those previously reported.

CONCLUSIONS

Our findings confirm that large numbers of patients with a representative variety of CMT subtypes have been enrolled and that the frequency of achieving a molecular diagnosis and distribution of the CMT subtypes reflects those previously reported. Measures of severity are similar, though not identical, to results from smaller series. This study confirms that it is possible to assess patients in a uniform way between international centres, which is critical for the planned natural history study and future clinical trials. These data will provide a representative baseline for longitudinal studies of CMT.

CLINICAL TRIAL REGISTRATION

ID number NCT01193075.

PMP22 related neuropathies: Charcot-Marie-Tooth disease type 1A and Hereditary Neuropathy with liability to Pressure Palsies

PMP22 related neuropathies comprise (1) PMP22 duplications leading to Charcot-Marie-Tooth disease type 1A (CMT1A), (2) PMP22 deletions, leading to Hereditary Neuropathy with liability to Pressure Palsies (HNPP), and (3) PMP22 point mutations, causing both phenotypes. Overall prevalence of CMT is usually reported as 1:2,500, epidemiological studies show that 20-64% of CMT patients carry the PMP22 duplication. The prevalence of HNPP is not well known. CMT1A usually presents in the first two decades with difficulty walking or running. Distal symmetrical muscle weakness and wasting and sensory loss is present, legs more frequently and more severely affected than arms. HNPP typically leads to episodic, painless, recurrent, focal motor and sensory peripheral neuropathy, preceded by minor compression on the affected nerve. Electrophysiological evaluation is needed to determine whether the polyneuropathy is demyelinating. Sonography of the nerves can be useful. Diagnosis is confirmed by finding respectively a PMP22 duplication, deletion or point mutation. Differential diagnosis includes other inherited neuropathies, and acquired polyneuropathies. The mode of inheritance is autosomal dominant and de novo mutations occur. Offspring of patients have a chance of 50% to inherit the mutation from their affected parent. Prenatal testing is possible; requests for prenatal testing are not common. Treatment is currently symptomatic and may include management by a rehabilitation physician, physiotherapist, occupational therapist and orthopaedic surgeon. Adult CMT1A patients show slow clinical progression of disease, which seems to reflect a process of normal ageing. Life expectancy is normal.

X-linked Charcot-Marie-Tooth disease predominates in a cohort of multiethnic Malaysian patients

INTRODUCTION

Data regarding Charcot-Marie-Tooth disease is lacking in Southeast Asian populations. We investigated the frequency of the common genetic mutations in a multiethnic Malaysian cohort.

METHODS

Patients with features of Charcot-Marie-Tooth disease or hereditary liability to pressure palsies were investigated for PMP22 duplication, deletion, and point mutations and GJB1, MPZ, and MFN2 point mutations.

RESULTS

Over a period of 3 years, we identified 25 index patients. A genetic diagnosis was reached in 60%. The most common were point mutations in GJB1, accounting for X-linked Charcot-Marie-Tooth disease (24% of the total patient population), followed by PMP22 duplication causing Charcot-Marie-Tooth disease type 1A (20%). We also discovered 2 novel GJB1 mutations, c.521C>T (Proline174Leucine) and c.220G>A (Valine74Methionine).

CONCLUSIONS

X-linked Charcot-Marie-Tooth disease was found to predominate in our patient cohort. We also found a better phenotype/genotype correlation when applying a more recently recommended genetic approach to Charcot-Marie-Tooth disease.