Different clinical and magnetic resonance imaging features between Charcot-Marie-Tooth disease type 1A and 2A

Characterization of Great Toe Extension Strength Using ToeScale-A Novel Portable Device

Great toe strength (GTS) weakness is linked to declines in balance and mobility. Accurately assessing GTS, particularly great toe extension strength (GTES), is often neglected in clinical evaluations due to cumbersome and subjective methods. This study aims to characterize the force development curve output from the ToeScale and examine GTES variations with age, sex, BMI, and grip strength (GS) using traditional analyses and machine learning (ML). We conducted a pilot, cross-sectional feasibility study with convenience samples. We assessed GS using a hand-grip dynamometer and GTES using the ToeScale. The data analysis included descriptive statistics, correlations, independent samples t-tests, and accuracy and area under the curve (AUC) scores for three ML models. Thirty-one participants (males: 9; females: 22), 14 young (18-24 years) and 17 older (>65 years) adults, participated in the study. Males had significantly higher peak GTES than females in both age groups. The associations of GTES parameters with BMI and GS varied by age and sex. The ML model accuracies and AUC scores were low-moderate but aligned with traditional analyses. Future studies with larger samples and optimized ML models are needed.

Lower limb muscle MRI fat fraction is a responsive outcome measure in CMT X1, 1B and 2A

OBJECTIVE

With potential therapies for many forms of Charcot-Marie-Tooth disease (CMT), responsive outcome measures are urgently needed for clinical trials. Quantitative lower limb MRI demonstrated progressive calf intramuscular fat accumulation in the commonest form, CMT1A with large responsiveness. In this study, we evaluated the responsiveness and validity in the three other common forms, due to variants in GJB1 (CMTX1), MPZ (CMT1B) and MFN2 (CMT2A).

METHODS

22 CMTX1, 21 CMT1B and 21 CMT2A patients and matched controls were assessed at a 1-year interval. Intramuscular fat fraction (FF) was evaluated using three-point Dixon MRI at thigh and calf level along with clinical measures including CMT examination score, clinical strength assessment, CMT-HI and plasma neurofilament light chain.

RESULTS

All patient groups had elevated muscle fat fraction at thigh and calf levels, with highest thigh FF and atrophy in CMT2A. There was moderate correlation between calf muscle FF and clinical measures (CMTESv2 rho = 0.405; p = 0.001, ankle MRC strength rho = -0.481; p < 0.001). Significant annualised progression in calf muscle FF was seen in all patient groups (CMTX1 2.0 ± 2.0%, p < 0.001, CMT1B 1.6 ± 2.1% p = 0.004 and CMT2A 1.6 ± 2.1% p = 0.002). Greatest increase was seen in patients with 10-70% FF at baseline (calf 2.7 ± 2.3%, p < 0.0001 and thigh 1.7 ± 2.1%, p = 0.01).

INTERPRETATION

Our results confirm that calf muscle FF is highly responsive over 12 months in three additional common forms of CMT which together with CMT1A account for 90% of genetically confirmed cases. Calf muscle MRI FF should be a valuable outcome measure in upcoming CMT clinical trials.

Quantified fat fraction as biomarker assessing disease severity in rare Charcot-Marie-Tooth subtypes

Objective

Charcot-Marie-Tooth (CMT) disease is the most common inherited neuromuscular disorder. Multi-echo Dixon MRI technique is a highly sensitive method for quantifying muscle fatty infiltration, which may provide excellent value for the assessment of CMT. Due to the rareness of the disease, its use in CMT disease has been rarely evaluated, especially in subtypes.

Methods

Thirty-four CMT1 patients, 25 CMT2 patients, and 10 healthy controls were recruited. All of the recruited CMT1 patients are CMT1A with PMP22 duplication. Among CMT2 patients, 7 patients are CMT2A with MFN2 mutation, and 7 patients have SORD mutations. Multi-echo Dixon MRI imaging was performed. The fat fractions (FFs) of 5 muscle compartments of the leg were measured at proximal, middle, and distal levels by two specialized musculoskeletal radiologists. Comparisons between CMT1, CMT2, and genetically defined subtypes were conducted.

Results

A proximal-distal gradient (27.6 ± 15.9, 29.9 ± 19.7, and 40.5 ± 21.4, p = 0.015) with a peroneal predominance (p = 0.001) in fat distribution was observed in CMT1. Significant differences in the soleus muscle FFs at proximal (19.1 ± 14.7 vs. 34.8 ± 25.1, p = 0.034) and medial levels (23.5 ± 21 vs. 38.0 ± 25.6, p = 0.044) were observed between CMT1 and CMT2 patients. Between PMP2 duplication and MFN2 mutation group, a significant difference in the soleus muscle FF was also observed (23.5 ± 21.0 vs. 54.7 ± 20.2, p = 0.039). Prominent correlations of calf muscle FFs with functional scores were observed.

Discussion

Multi-echo Dixon MRI imaging is a valuable tool for assessing disease severity in CMT. The difference in patterns of fatty infiltration of CMT subtypes is first reported, which could provide references when making targeted training plans.

The Impact of Fatty Infiltration on MRI Segmentation of Lower Limb Muscles in Neuromuscular Diseases: A Comparative Study of Deep Learning Approaches

BACKGROUND

Deep learning methods have been shown to be useful for segmentation of lower limb muscle MRIs of healthy subjects but, have not been sufficiently evaluated on neuromuscular disease (NDM) patients.

PURPOSE

Evaluate the influence of fat infiltration on convolutional neural network (CNN) segmentation of MRIs from NMD patients.

STUDY TYPE

Retrospective study.

SUBJECTS

Data were collected from a hospital database of 67 patients with NMDs and 14 controls (age: 53 ± 17 years, sex: 48 M, 33 F). Ten individual muscles were segmented from the thigh and six from the calf (20 slices, 200 cm section).

FIELD STRENGTH/SEQUENCE

A 1.5 T. Sequences: 2D T1 -weighted fast spin echo. Fat fraction (FF): three-point Dixon 3D GRE, magnetization transfer ratio (MTR): 3D MT-prepared GRE, T2: 2D multispin-echo sequence.

ASSESSMENT

U-Net 2D, U-Net 3D, TransUNet, and HRNet were trained to segment thigh and leg muscles (101/11 and 95/11 training/validation images, 10-fold cross-validation). Automatic and manual segmentations were compared based on geometric criteria (Dice coefficient [DSC], outlier rate, absence rate) and reliability of measured MRI quantities (FF, MTR, T2, volume).

STATISTICAL TESTS

Bland-Altman plots were chosen to describe agreement between manual vs. automatic estimated FF, MTR, T2 and volume. Comparisons were made between muscle populations with an FF greater than 20% (G20+) and lower than 20% (G20-).

RESULTS

The CNNs achieved equivalent results, yet only HRNet recognized every muscle in the database, with a DSC of 0.91 ± 0.08, and measurement biases reaching -0.32% ± 0.92% for FF, 0.19 ± 0.77 for MTR, -0.55 ± 1.95 msec for T2, and - 0.38 ± 3.67 cm3 for volume. The performances of HRNet, between G20- and G20+ decreased significantly.

DATA CONCLUSION

HRNet was the most appropriate network, as it did not omit any muscle. The accuracy obtained shows that CNNs could provide fully automated methods for studying NMDs. However, the accuracy of the methods may be degraded on the most infiltrated muscles (>20%).

EVIDENCE LEVEL

4.

TECHNICAL EFFICACY

Stage 1.

An integrative analysis of genotype-phenotype correlation in Charcot Marie Tooth type 2A disease with MFN2 variants: A case and systematic review

Dominant genetic variants in the mitofusin 2 (MFN2) gene lead to Charcot-Marie-Tooth type 2A (CMT2A), a neurodegenerative disease caused by genetic defects that directly damage axons. In this study, we reported a proband with a pathogenic variant in the GTPase domain of MFN2, c.494A > G (p.His165Arg). To date, at least 184 distinct MFN2 variants identified in 944 independent probands have been reported in 131 references. However, the field of medical genetics has long been challenged by how genetic variation in the MFN2 gene is associated with disease phenotypes. Here, by collating the MFN2 variant data and patient clinical information from Leiden Open Variant Database 3.0, NCBI clinvar database, and available related references in PubMed, we determined the mutation frequency, age of onset, sex ratio, and geographical distribution. Furthermore, the results of an analysis examining the relationship between variants and phenotypes from multiple genetic perspectives indicated that insertion and deletions (indels), copy number variants (CNVs), duplication variants, and nonsense mutations in single nucleotide variants (SNVs) tend to be pathogenic, and the results emphasized the importance of the GTPase domain to the structure and function of MFN2. Overall, three reliable classification methods of MFN2 genotype-phenotype associations provide insights into the prediction of CMT2A disease severity. Of course, there are still many MFN2 variants that have not been given clear clinical significance, which requires clinicians to make more accurate clinical diagnoses.

Quantification of muscle involvement in familial amyloid polyneuropathy using MRI

BACKGROUND AND PURPOSE

Transthyretin familial amyloid polyneuropathy (TTR-FAP) is a rare genetic disease with autosomal-dominant inheritance. In this study, we aimed to quantify fatty infiltration (fat fraction [FF]) and magnetization transfer ratio (MTR) in individual muscles of patients with symptomatic and asymptomatic TTR-FAP using magnetic resonance imaging. Secondarily, we aimed to assess correlations with clinical and electrophysiological variables.

METHODS

A total of 39 patients with a confirmed mutation in the TTR gene (25 symptomatic and 14 asymptomatic) and 14 healthy volunteers were included. A total of 16 muscles were manually delineated in the nondominant lower limb from T1-weighted anatomical images. The corresponding masks were propagated on the MTR and FF maps. Detailed neurological and electrophysiological examinations were conducted in each group.

RESULTS

The MTR was decreased (42.6 AU; p = 0.001) and FF was elevated (14%; p = 0.003) in the lower limbs of the symptomatic group, with preferential posterior and lateral involvement. In the asymptomatic group, elevated FF was quantified in the gastrocnemius lateralis muscle (11%; p = 0.021). FF was significantly correlated with disease duration (r = 0.49, p = 0.015), neuropathy impairment score for the lower limb (r = 0.42, p = 0.041), Overall Neuropathy Limitations Scale score (r = 0.49, p = 0.013), polyneuropathy disability score (r = 0.57, p = 0.03) and the sum of compound muscle action potential (r = 0.52, p = 0.009). MTR was strongly correlated to FF (r = 0.78, p < 0.0001), and a few muscles with an FF within the normal range had a reduced MTR.

CONCLUSION

These observations suggest that FF and MTR could be interesting biomarkers in TTR-FAP. In asymptomatic patients, FF in the gastrocnemius lateralis muscle could be a good indicator of the transition from an asymptomatic to a symptomatic form of the disease. MTR could be an early biomarker of muscle alterations.

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.

Intrinsic muscles of the foot: Anatomy, function, rehabilitation

The intrinsic muscles of the foot are underappreciated structures in evaluating and treating lower extremity dysfunction. These muscles play a crucial role in the proper function of the foot during sport activities. The functions of these muscles are not generally well understood. Intrinsic dysfunction can lead to a variety of problems. Therefore, it is important for clinicians to have a good understanding of the anatomy and function of the intrinsic foot muscles in order to properly diagnose and treat foot injuries in patients. Published research on the rehabilitation of the intrinsic muscles provides insight into the function as well as benefits of treatment. The purpose of this review is to summarize the published research on the anatomy, function, contribution to pathology, as well as rehabilitation options for the intrinsic muscles of the foot.

Magnetic resonance imaging-based lower limb muscle evaluation in Charcot-Marie-Tooth disease type 1A patients and its correlation with clinical data

We aimed to derive comprehensive MRI parameters that reflect intramuscular fat infiltration severity for designated lower extremity levels, based on semiquantitative analyses in Charcot-Marie-Tooth disease type 1A (CMT1A) patients. We reviewed lower extremity MRIs of 116 CMT1A patients. Intramuscular fat infiltration grading using the Mercuri scale was performed for the non-dominant lower extremity at three levels (proximal, mid, and distal) for the thigh and at two levels (proximal and distal) for the lower leg. Based on MRI results, the following parameters were calculated for each level and for entire muscles: fat infiltration proportion (FIP), significant fat infiltration proportion (SigFIP), and severe fat infiltration proportion (SevFIP). The relationships between the MRI parameters and clinical data were evaluated using Spearman’s correlation analysis. FIP, SigFIP, and SevFIP measured for entire muscles significantly correlated with Charcot-Marie-Tooth Neuropathy Score (p < 0.001), functional disability scale (p < 0.001), 10-m walk test time (p = 0.0003, 0.0010, and 0.0011), and disease duration (p < 0.001). Similar correlations were demonstrated for FIP, SigFIP, and SevFIP acquired from the lower leg. Our MRI parameters obtained through semiquantitative analyses of muscles significantly correlated with clinical parameters in CMT1A patients, suggesting their potential applicability as imaging markers for clinical severity.

The GDAP1 p.Glu222Lys Variant-Weak Pathogenic Effect, Cumulative Effect of Weak Sequence Variants, or Synergy of Both Factors?

Charcot−Marie−Tooth disorders (CMT) represent a highly heterogeneous group of diseases of the peripheral nervous system in which more than 100 genes are involved. In some CMT patients, a few weak sequence variants toward other CMT genes are detected instead of one leading CMT mutation. Thus, the presence of a few variants in different CMT-associated genes raises the question concerning the pathogenic status of one of them. In this study, we aimed to analyze the pathogenic effect of c.664G>A, p.Glu222Lys variant in the GDAP1 gene, whose mutations are known to be causative for CMT type 4A (CMT4A). Due to low penetrance and a rare occurrence limited to five patients from two Polish families affected by the CMT phenotype, there is doubt as to whether we are dealing with real pathogenic mutation. Thus, we aimed to study the pathogenic effect of the c.664G>A, p.Glu222Lys variant in its natural environment, i.e., the neuronal SH-SY5Y cell line. Additionally, we have checked the pathogenic status of p.Glu222Lys in the broader context of the whole exome. We also have analyzed the impact of GDAP1 gene mutations on the morphology of the transfected cells. Despite the use of several tests to determine the pathogenicity of the p.Glu222Lys variant, we cannot point to one that would definitively solve the problem of pathogenicity.

A Rare Phenotype of Uncommon Charcot–Marie–Tooth Genotypes Complicated With Inflammation Evaluated by Genetics and Magnetic Resonance Neurography

The pathogenesis of Charcot–Marie–Tooth (CMT) disease, an inherited peripheral neuropathy, is associated with more than 60 nuclear genes. We reported a rare phenotype of the uncommon CMT genotype complicated with neuroinflammation, that is, an MPZ mutation, NC_000001.11 (NM_000530.6): c.308G > C detected by next-generation sequencing. Moreover, we present a case of the CMT type 1B, with atypical presentation as two patterns of hypertrophy in the brachial and lumbosacral plexus, as well as enhancement in the cauda equina and nerve roots on multimodal magnetic resonance neurography (MRN). MRN assessment facilitated the identification of coexisting neuroinflammation and provided more evidence, especially for patients with atypical symptoms in hereditary sensory and motor neuropathy, who could benefit from immunotherapy.

Candidate imaging biomarkers for PMP22-related inherited neuropathies

OBJECTIVE

Charcot-Marie-Tooth type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsy (HNPP) are caused by mutations to the peripheral myelin protein 22 (PMP22) gene. A need exists for sensitive and reliable biomarkers of progression and treatment response. Magnetic resonance imaging (MRI) metrics of nerve pathology and morphology were investigated for this purpose.

METHODS

MRI was performed at 3.0 T in the thigh of CMT1A (N = 11) and HNPP patients (N = 12) and controls (N = 23). Three potential imaging biomarkers of the sciatic nerve were investigated: 1) magnetization transfer ratio (MTR), which assays myelin content, and 2) cross-sectional area (CSA) and 3) circularity, which assay morphological changes. Potential imaging biomarkers were compared across cohorts and assessed for relationships with disability in the legs (CMTESL ), compound motor action potentials (CMAP), and motor conduction velocities (MCV). Inter-rater reliability and test-retest repeatability were established for each imaging metric.

RESULTS

Significant differences in MTR, CSA, and circularity were observed in CMT1A relative to controls (p = 0.02, p < 0.001, and p = 0.003, respectively, via Wilcoxon rank-sum tests). Differences were not observed in the HNPP cohort. Significant relationships were observed between MTR and clinical metrics (CMTESL : p = 0.003, CMAP: p = 0.03, MCV: p = 0.01); and between CSA and electrophysiology (CMAP: p = 0.002, MCV: p < 0.001). All metrics were reliable and repeatable with MTR the most reliable (intraclass correlation coefficient [ICC] >0.999, CV = 0.30%) and repeatable (ICC = 0.84, CV = 3.16%).

INTERPRETATION

MTR, CSA, and circularity showed promise as reliable and sensitive biomarkers of CMT1A, but not HNPP. These warrant longitudinal investigation as response biomarkers in upcoming clinical trials of CMT1A, while other methods should be considered for HNPP.

Contemporary Review: The Foot and Ankle in Long-Distance Running

Distance runners represent a unique patient population. The cyclic activity associated with distance running leads to a high incidence of injury. Gait patterns, the extrinsic and intrinsic muscles of the foot and ankle, foot strike pattern, shoe wear considerations, alignment, and orthotics are also all important considerations that must be considered by the treating provider. The purpose of this work is to review relevant functional anatomy, recent studies on gait patterns in running, orthotics, and theory on how the body moves through space during running in order to better equip the clinician to treat long distance runners.

Randomized Phase 2 Study of ACE-083 in Patients With Charcot-Marie-Tooth Disease

BACKGROUND AND OBJECTIVES

The goal of this work was to determine whether locally acting ACE-083 is safe and well tolerated and increases muscle volume, motor function, and quality of life (QoL) in adults with Charcot-Marie-Tooth disease (CMT) type 1.

METHODS

This phase 2 study enrolled adults with CMT1 or CMTX (N = 63). Part 1 was open label and evaluated the safety and tolerability of different dose levels of ACE-083 for use in part 2. Part 2 was a randomized, placebo-controlled, 6-month study of 240 mg/muscle ACE-083 injected bilaterally into the tibialis anterior muscle, followed by a 6-month, open-label extension in which all patients received ACE-083. Pharmacodynamic endpoints included total muscle volume (TMV; primary endpoint), contractile muscle volume (CMV), and fat fraction. Additional secondary endpoints included 6-minute walk test, 10-m walk/run, muscle strength, and QoL. Safety was assessed with treatment-emergent adverse events (TEAEs) and clinical laboratory tests.

RESULTS

In part 1 (n = 18), ACE-083 was generally safe and well tolerated at all dose levels, with no serious adverse events, TEAEs of grade 3 or greater, or death reported. In part 2 (n = 45 enrolled, n = 44 treated), there was significantly greater change in TMV with ACE-083 compared with placebo (least-squares mean difference 13.5%; p = 0.0096). There was significant difference between ACE-083 and placebo for CMV and change in ankle dorsiflexion strength. Fat fraction and all other functional outcomes were not significantly improved by ACE-083. Moderate to mild injection-site reactions were the most common TEAEs.

DISCUSSION

Despite significantly increased TMV and CMV, patients with CMT receiving ACE-083 in tibialis anterior muscles did not demonstrate greater functional improvement compared with those receiving placebo.

TRIAL REGISTRATION INFORMATION

Clinical Trials Registration: NCT03124459.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that intramuscular ACE-083 is safe and well tolerated and increases total muscle volume after 6 months of treatment in adults with CMT1 or CMTX.

Proximal nerve MR neurography with diffusion tensor imaging in differentiating subtypes of Charcot-Marie-Tooth disease

OBJECTIVES

To evaluate the feasibility of proximal nerve MR neurography with diffusion tensor imaging (DTI) for differentiating Charcot-Marie-Tooth (CMT) 1A, CMT2, and healthy controls.

METHODS

The diameters, fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) of L4-L5 nerve roots, femoral nerve (FN), and sciatic nerve (SN) were compared. Receiver operating characteristic (ROC) curve analyses were conducted to evaluate the diagnostic performance. DeLong's tests were applied to compare multiple ROC curves. Intraclass correlation coefficients were calculated for interobserver agreement assessment.

RESULTS

The diameters of the L4 nerve root, L5 nerve root, and SN of CMT1A patients were significantly larger than those of CMT2 patients and healthy controls. The FA values of all measured proximal nerves were significantly higher in controls (0.46 ± 0.09, 0.46 ± 0.08, 0.45 ± 0.07, and 0.48 ± 0.08) than in CMT1A patients (0.30 ± 0.09, 0.29 ± 0.06, 0.35 ± 0.08, and 0.29 ± 0.09). The FA values of the L5 nerve root, FN, and SN were significantly higher in controls (0.46 ± 0.08, 0.45 ± 0.07, and 0.48 ± 0.08) than in CMT2 patients (0.36 ± 0.06, 0.34 ± 0.07, and 0.34 ± 0.10). The MD and RD values of the L5 nerve root in CMT1A patients (1.59 ± 0.21 and 1.37 ± 0.21) were higher than those in CMT2 patients (1.31 ± 0.17 and 1.05 ± 0.14). The AUCs of the above parameters ranged from 0.780 to 1.000. For the measurements of nerve diameters, the ICC ranged from 0.91 to 0.97. For the measurements of DTI metrics, the ICC ranged from 0.87 to 0.97.

CONCLUSIONS

MR neurography with DTI is able to differentiate CMT1A patients, CMT2 patients, and healthy controls.

KEY POINTS

• MR neurography with diffusion tensor imaging of the L4-5 nerve roots, proximal femoral nerve, and proximal sciatic nerve is able to discriminate CMT1A, CMT2, and healthy controls. • This method provides an alternative for the diagnosis and discrimination of CMT1A and CMT2, which is crucial for clinical management.

Muscle "islands": An MRI signature distinguishing neurogenic from myopathic causes of early onset distal weakness

Muscle MRI has an increasing role in diagnosis of inherited neuromuscular diseases, but no features are known which reliably differentiate myopathic and neurogenic conditions. Using patients presenting with early onset distal weakness, we aimed to identify an MRI signature to distinguish myopathic and neurogenic conditions. We identified lower limb MRI scans from patients with either genetically (n = 24) or clinically (n = 13) confirmed diagnoses of childhood onset distal myopathy or distal spinal muscular atrophy. An initial exploratory phase reviewed 11 scans from genetically confirmed patients identifying a single potential discriminatory marker concerning the pattern of fat replacement within muscle, coined "islands". This pattern comprised small areas of muscle tissue with normal signal intensity completely surrounded by areas with similar intensity to subcutaneous fat. In the subsequent validation phase, islands correctly classified scans from all 12 remaining genetically confirmed patients, and 12/13 clinically classified patients. In the genetically confirmed patients MRI classification of neurogenic/myopathic aetiology had 100% accuracy (24/24) compared with 65% accuracy (15/23) for EMG, and 79% accuracy (15/19) for muscle biopsy. Future studies are needed in other clinical contexts, however the presence of islands appears to highly suggestive of a neurogenic aetiology in patients presenting with early onset distal motor weakness.

Muscle MRI as a Useful Biomarker in Hereditary Transthyretin Amyloidosis: A Pilot Study

Hereditary transthyretin amyloidosis (ATTRv, v for variant) is a severe and heterogeneous multisystem condition with a prevalent peripheral nervous system impairment, due to mutations in the transthyretin gene. Considering the introduction of different disease-modifying therapies in the last few years, a need of reliable biomarkers is emerging. In this study, we evaluated muscle MRI in a cohort of ATTRv patients in order to establish if the severity of muscle involvement correlated with disease severity. Linear regression analysis showed a significant positive correlation between the total fatty infiltration score and NIS, NIS-LL, and Norfolk, and an inverse correlation with Sudoscan registered from feet. In conclusion, we demonstrated the role of muscle MRI in ATTRv as possible disease biomarker, both for diagnostic purposes and for assessing the severity of the disease.

Imaging of the Pes Cavus Deformity

Direct-type cavus foot deformities are most commonly encountered and are primarily sagittal plane deformities. Direct deformities should be delineated from rarer triplane pes cavovarus deformities. The lateral weight-bearing radiograph is the cornerstone of imaging evaluation of direct pes cavus foot deformity. The apex of Meary talo-first metatarsal angle on the lateral radiograph represents the pinnacle of the cavus deformity and assists in subclassification of the deformity. With routine application, ancillary radiographic imaging techniques, such as the modified Saltzman view or the modified Coleman block test, can give valuable insight into deformity assessment and surgical planning.

Gait parameters as tools for analyzing phenotypic alterations of a mouse model of Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT), a genetically heterogeneous group of diseases in the peripheral nervous system, is characterized by progressive and symmetrical distal weakness resulting in gait abnormality. The necessity of the diagnostic and prognostic biomarkers has been raised for both basic research and clinical practice in CMT. Since biomarkers for animal study of CMT are limited, we evaluated the feasibility of gait parameters as tool for measuring disease phenotype of CMT mouse model. Using a Trembler-J (Tr-J) mouse, a CMT type 1 (CMT1) mouse model, we analyzed kinematic parameters such as angles of hip, knee and ankle (sagittal plane), and spatial parameters including step width and stride length (transverse plane). Regarding of kinematic parameters, Tr-J mice exhibited less plantarflexed ankle during the swing phase and more dorsiflexed ankle at the terminal stance compared to control mice. The range of motion in ankle angle of Tr-J mice was significantly greater than that of control mice. In spatial parameter, Tr-J mice exhibited wider step width compared to control mice. These results are similar to previously reported gait patterns of CMT1 patients. In comparison with other markers such as nerve conduction study and rotarod test, gait parameters dynamically reflected the disease progression of CMT1 mice. Therefore, these data imply that gait parameters can be used as useful tools to analyzed the disease phenotype and progression during preclinical study of peripheral neuropathy such as CMT.

Clinical and Neuroimaging Features in Charcot-Marie-Tooth Patients with GDAP1 Mutations

Background and Purpose

Mutations in the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) are known to cause Charcot-Marie-Tooth disease (CMT). These mutations are very rare in most countries, but not in certain Mediterranean countries. The purpose of this study was to identify the clinical and neuroimaging characteristics of Korean CMT patients with GDAP1 mutations.

Methods

Gene sequencing was applied to 1,143 families in whom CMT had been diagnosed from 2005 to 2020. PMP22 duplication was found in 344 families, and whole-exome sequencing was performed in 699 patients. Magnetic resonance imaging (MRI) were obtained using either a 1.5-T or 3.0-T MRI system.

Results

We found ten patients from eight families with GDAP1 mutations: five with autosomal dominant (AD) CMT type 2K (three families with p.R120W and two families with p.Q218E) and three with autosomal recessive (AR) intermediate CMT type A (two families with homozygous p.H256R and one family with p.P111H and p.V219G mutations). The frequency was about 1.0% exclusive of the PMP22 duplication, which is similar to that in other Asian countries. There were clinical differences among AD GDAP1 patients according to mutation sites. Surprisingly, fat infiltrations evident in lower-limb MRI differed between AD and AR patients. The posterior-compartment muscles in the calf were affected early and predominantly in AD patients, whereas AR patients showed fat infiltration predominantly in the anterolateral-compartment muscles.

Conclusions

This is the first cohort report on Korean patients with GDAP1 mutations. The patients with AD and AR inheritance routes exhibited different clinical and neuroimaging features in the lower extremities. We believe that these results will help to expand the knowledge of the clinical, genetic, and neuroimaging features of CMT.

Alanyl-tRNA synthetase 1 (AARS1) gene mutation in a family with intermediate Charcot-Marie-Tooth neuropathy

BACKGROUND

Alanyl-tRNA synthetase 1 (AARS1) gene encodes a ubiquitously expressed class II enzyme that catalyzes the attachment of alanine to the cognate tRNA. AARS1 mutations are frequently responsible for autosomal dominant Charcot-Marie-Tooth disease type 2N (CMT2N).

OBJECTIVE

To identify pathogenic mutation in the Korean patients with CMT and distal hereditary motor neuronopathy (dHMN).

METHODS

We screened AARS1 mutations in 373 unrelated CMT families including 318 axonal CMT, 36 dHMN, and 19 intermediate CMT (Int-CMT) who were negative for 17p12 (PMP22) duplication or deletion using whole exome sequencing and targeted sequencing of CMT-related genes.

RESULTS

This study identified an early onset Int-CMT family harboring an AARS1 p.Arg329His mutation which was previously reported as pathogenic in French and Australian families. The mutation was located in the highly conserved tRNA binding domain and several in silico analyses suggested pathogenic prediction of the mutations. The patients harboring p.Arg329His showed clinically similar phenotypes of the early onset and electrophysiological intermediate type as those in Australian patients with same mutation. We also found a novel c.2564A>G (p.Gln855Arg) in a CMT2 patient, but its' pathogenic role was uncertain (variant of uncertain significance).

CONCLUSION

This study suggests that the frequency of the AARS1 mutations appears to be quite low in Korean CMT. This is the first report of the AARS1 mutation in Korean CMT patients and will be helpful for the exact molecular diagnosis and treatment of Int-CMT patients.

Fat fraction distribution in lower limb muscles of patients with CMT1A: A quantitative MRI study

OBJECTIVE

To quantitatively describe the MRI fat infiltration pattern of muscle degeneration in Charcot-Marie-Tooth (CMT) type 1A (CMT1A) disease and to look for correlations with clinical variables.

METHODS

MRI fat fraction was assessed in lower-limb musculature of patients with CMT1A and healthy controls. More particularly, 14 muscle compartments were selected at leg and thigh levels and for proximal, distal, and medial slices. Muscle fat infiltration profile was determined quantitatively in each muscle compartment and along the entire volume of acquisition to determine a length-dependent gradient of fat infiltration. Clinical impairment was evaluated with muscle strength measurements and CMT Examination Scores (CMTESs).

RESULTS

A total of 16 patients with CMT1A were enrolled and compared to 11 healthy controls. Patients with CMT1A showed a larger muscle fat fraction at leg and thigh levels with a proximal-to-distal gradient. At the leg level, the largest fat infiltration was quantified in the anterior and lateral compartments. CMTES was correlated with fat fraction, especially in the anterior compartment of leg muscles. Strength of plantar flexion was also correlated with fat fraction of the posterior compartments of leg muscles.

CONCLUSION

On the basis of quantitative MRI measurements combined with a dedicated segmentation method, muscle fat infiltration quantified in patients with CMT1A disclosed a length-dependent peroneal-type pattern of fat infiltration and was correlated to main clinical variables. Quantification of fat fraction at different levels of the leg anterior compartment might be of interest in future clinical trials.

Length-dependent MRI of hereditary neuropathy with liability to pressure palsies

OBJECTIVE

Hereditary neuropathy with liability to pressure palsies (HNPP) is caused by heterozygous deletion of the peripheral myelin protein 22 (PMP22) gene. Patients with HNPP present multifocal, reversible sensory/motor deficits due to increased susceptibility to mechanical pressure. Additionally, age-dependent axonal degeneration is reported. We hypothesize that length-dependent axonal loss can be revealed by MRI, irrespective of the multifocal phenotype in HNPP.

METHODS

Nerve and muscle MRI data were acquired in the proximal and distal leg of patients with HNPP (n = 10) and matched controls (n = 7). More specifically, nerve magnetization transfer ratios (MTR) were evaluated to assay proximal-to-distal gradients in nerve degeneration, while intramuscular fat percentages (Fper ) were evaluated to assay muscle fat replacement following denervation. Neurological disabilities were assessed via the Charcot-Marie-Tooth neuropathy score (CMTNS) for correlation with MRI.

RESULTS

Fper values were elevated in HNPP proximal muscle (9.8 ± 2.2%, P = 0.01) compared to controls (6.9 ± 1.0%). We observed this same elevation of HNPP distal muscles (10.5 ± 2.5%, P < 0.01) relative to controls (6.3 ± 1.1%). Additionally, the amplitude of the proximal-to-distal gradient in Fper was more significant in HNPP patients than controls (P < 0.01), suggesting length-dependent axonal loss. In contrast, nerve MTR values were similar between HNPP subjects (sciatic/tibial nerves = 39.4 ± 2.0/34.2 ± 2.5%) and controls (sciatic/tibial nerves = 37.6 ± 3.8/35.5 ± 1.2%). Proximal muscle Fper values were related to CMTNS (r = 0.69, P = 0.03), while distal muscle Fper and sciatic/tibial nerve MTR values were not related to disability.

INTERPRETATION

Despite the multifocal nature of the HNPP phenotype, muscle Fper measurements relate to disability and exhibit a proximal-to-distal gradient consistent with length-dependent axonal loss, suggesting that Fper may be a viable biomarker of disease progression in HNPP.

BAG3 p.Pro209Ser mutation identified in a Chinese family with Charcot-Marie-Tooth disease

Bcl2-associated athanogene 3 (BAG3) gene mutations cause dilated cardiomyopathy and myofibrillar myopathy. Recently, a novel c.625C>T (p.Pro209Ser) mutation in BAG3 was reported to cause axonal Charcot-Marie-Tooth (CMT) disease in three families. Here, we describe two patients with adult-onset and moderate CMT in a Chinese family. Nerve conduction velocity studies revealed an axonal sensorimotor neuropathy, which was supported by sural nerve biopsy. Lower limb magnetic resonance imaging (MRI) revealed fatty infiltration more severe in the soleus and deep posterior compartment muscles than in the medial gastrocnemius and anterior compartment muscles. Whole exome sequencing identified the same c.625C>T (p.Pro209Ser) mutation in BAG3, which co-segregated with the CMT disease in this family. This study further enforces the association between BAG3 gene and CMT disease, indicating that BAG3 should be considered in the genetic testing for CMT. The p.Pro209Ser mutation with different ethnic origins might be another hotspot mutation of BAG3. MRI is helpful to detect accurate extent of muscle involvement.

Muscle fat quantification using magnetic resonance imaging: case-control study of Charcot-Marie-Tooth disease patients and volunteers

BACKGROUND

This study aimed to evaluate the potential value of 3D multiple gradient echo Dixon-based magnetic resonance imaging (MRI) sequence as a tool for thigh intramuscular fat quantification in Charcot-Marie-Tooth disease (CMT) patients.

METHODS

A prospective comparison study comprising 18 CMT patients and 18 age/sex-matched volunteers was performed. MRI including 3D multiple gradient echo Dixon-based imaging was performed for each subject. Region of interest analyses were performed at the upper and lower third of both thighs. The two-sample t-test or Wilcoxon rank sum test was used for intergroup comparison of the mean muscle fat fraction. Intraclass correlation coefficients were used to evaluate the interobserver agreement and test-retest reproducibility. Semiquantitive analysis using the Goutallier classification (Grades 0-4) was performed on T1-weighted images in upper thigh muscles. For Goutallier Grade 0 muscles, comparison of the mean intramuscular fat fraction between volunteers and CMT patients was performed.

RESULTS

The interobserver agreements were excellent for all measurements (intraclass correlation coefficients > 0.8). Mean muscle fat fractions were significantly higher in all the measured muscles of CMT patients (P < 0.05) except in the adductor magnus in the upper thigh (P = 0.109). Goutallier Grade 0 muscles of the CMT patients showed a significantly higher mean fat fraction compared with that of the volunteers (P < 0.05).

CONCLUSIONS

3D multiple gradient echo Dixon-based MRI is a reproducible and sensitive technique which can reveal a significant difference in the fat fraction of thigh muscle, including comparison between Goutallier Grade 0 muscles, between CMT patients and volunteers.

Diffusion tensor imaging of the sciatic nerve in Charcot-Marie-Tooth disease type I patients: a prospective case-control study

OBJECTIVES

This study aimed to evaluate whether diffusion tensor imaging (DTI) parameters and cross-sectional area (CSA) can differentiate between the sciatic nerve of Charcot-Marie-Tooth (CMT) disease type I (demyelinating form) patients and that of controls.

METHODS

This prospective comparison study included 18 CMT type I patients and 18 age/sex-matched volunteers. Magnetic resonance imaging including DTI and axial T2-weighted Dixon sequence was performed for each subject. Region of interest analysis was independently performed by two radiologists on each side of the sciatic nerve at four levels: hamstring tendon origin (level 1), lesser trochanter of the femur (level 2), gluteus maximus tendon insertion (level 3), and mid-femur (level 4). Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated. The CSA of the sciatic nerve bundle was measured using axial water-only image at each level. Comparisons of DTI parameters between the two groups were performed using the two-sample t test and Mann-Whitney U test. Interobserver agreement analysis was also conducted.

RESULTS

Interobserver agreement was excellent for all DTI parameter analyses. FA was significantly lower at all four levels in CMT patients than controls. RD, MD, and CSA were significantly higher at all four levels in CMT patients. AD was significantly higher at level 2 in CMT patients.

CONCLUSION

DTI assessment of the sciatic nerve is reproducible and can discriminate the demyelinating nerve pathology of CMT type I patients from normal nerves. The CSA of the sciatic nerve is also a potential parameter for diagnosing nerve abnormality in CMT type I patients.

KEY POINTS

• Diffusion tensor imaging parameters of the sciatic nerve at proximal to mid-femur level revealed significant differences between the Charcot-Marie-Tooth disease patients and controls. • The cross-sectional area of the sciatic nerve was significantly larger in the Charcot-Marie-Tooth disease patients. • Interobserver agreement was excellent (intraclass coefficient > 0.8) for all diffusion tensor imaging parameter analyses.

A novel AIFM1 mutation in a Chinese family with X-linked Charcot-Marie-Tooth disease type 4

X-linked Charcot-Marie-Tooth disease type 4 (CMTX4), caused by AIFM1 (Apoptosis-Inducing Factor, Mitochondrion associated 1) mutations and associated with deafness and cognitive impairment, is a rare subtype of Charcot-Marie-Tooth disease. Here, we report a novel missense variant of AIFM1 in a X-linked recessive Chinese family with childhood-onset, slowly progressive, isolated axonal motor and sensory neuropathy. Calf magnetic resonance imaging revealed fatty infiltration and atrophy severely involving the muscles of peroneal compartment. Pathologies exhibited abnormal mitochondrial morphology and accumulation in axoplasm of nerve fiber and subsarcolemmal area of muscle. A hemizygous variant (c.513G>A, p.Met171Ile) in the family was identified and was classified as likely pathogenic according to the standards and guidelines of the American College of Medical Genetics and Genomics. Our report expands the genetic spectrum of diseases related to AIFM1 mutations and indicates that fatty infiltration and atrophy of muscles in the peroneal compartment may be a feature of CMTX4 in early stage.

Axonal Charcot-Marie-Tooth neuropathy concurrent with distal and proximal weakness by translational elongation of the 3' UTR in NEFH

Mutations in the NEFH gene encoding the heavy neurofilament protein are usually associated with neuronal damage and susceptibility to amyotrophic lateral sclerosis (ALS). Recently, frameshift variants in NEFH (p.Asp1004Glnfs*58 and p.Pro1008Alafs*56) have been reported to be the underlying cause of axonal Charcot-Marie-Tooth disease type 2CC (CMT2CC). The frameshift mutation resulted in a stop loss and translation of a cryptic amyloidogenic element (CAE) encoded by the 3' untranslated region (UTR). This study also identified a de novo c.3015_3027dup frameshift mutation predicting p.Lys1010Glnfs*57 in NEFH from a CMT2 family with an atypical clinical symptom of prominent proximal weakness. This mutation is located near the previously reported frameshift mutations, suggesting a mutational hotspot. Lower limb magnetic resonance imaging (MRI) revealed marked hyperintense signal changes in the thigh muscles compared with those in the calf muscles. Therefore, this study suggests that the stop loss and translational elongations by the 3' UTR of the NEFH mutations may be a relatively frequent genetic cause of axonal peripheral neuropathy with the specific characteristics of proximal dominant weakness.

Locomotor and skeletal muscle abnormalities in trembler J neuropathic mice

INTRODUCTION

Patients with hereditary peripheral neuropathies exhibit characteristic deformities of the hands and feet and have difficulty ambulating. To examine to what extent neuropathic animals recapitulate these deficits, we studied trembler J (TrJ) mice, which model early-onset demyelinating neuropathy.

METHODS

A cohort of 4-month-old female wild type and neuropathic mice were evaluated for locomotor measurements, neuromuscular function, and skeletal muscle proteolysis and morphometry.

RESULTS

Utilizing the DigiGait imaging system, we identified pronounced alterations in forepaw and hindpaw angles and a decrease in hindpaw area on the treadmill in neuropathic rodents. Torque production by the tibialis anterior (TA) muscle was significantly weakened and was paralleled by a decrease in myofiber cross-sectional area and an increase in muscle tissue proteolysis.

DISCUSSION

Our findings in TrJ mice reflect the phenotypic presentation of the human neuropathy in which patients exhibit weakness of the TA muscle resulting in foot drop and locomotor abnormalities. Muscle Nerve 57: 664-671, 2018.

Distribution and genotype-phenotype correlation of GDAP1 mutations in Spain

Mutations in the GDAP1 gene can cause Charcot-Marie-Tooth disease. These mutations are quite rare in most Western countries but not so in certain regions of Spain or other Mediterranean countries. This cross-sectional retrospective multicenter study analyzed the clinical and genetic characteristics of patients with GDAP1 mutations across Spain. 99 patients were identified, which were distributed across most of Spain, but especially in the Northwest and Mediterranean regions. The most common genotypes were p.R120W (in 81% of patients with autosomal dominant inheritance) and p.Q163X (in 73% of autosomal recessive patients). Patients with recessively inherited mutations had a more severe phenotype, and certain clinical features, like dysphonia or respiratory dysfunction, were exclusively detected in this group. Dominantly inherited mutations had prominent clinical variability regarding severity, including 29% of patients who were asymptomatic. There were minor clinical differences between patients harboring specific mutations but not when grouped according to localization or type of mutation. This is the largest clinical series to date of patients with GDAP1 mutations, and it contributes to define the genetic distribution and genotype-phenotype correlation in this rare form of CMT.

Magnetic resonance neurography and diffusion tensor imaging of the peripheral nerves in patients with Charcot-Marie-Tooth Type 1A

INTRODUCTION

Investigation of peripheral neuropathies by magnetic resonance neurography (MRN) may provide increased diagnostic accuracy when performed in combination with diffusion tensor imaging (DTI). This study seeks to evaluate DTI in the detection of neuropathic abnormalities in Charcot-Marie-Tooth type 1A (CMT1A).

METHODS

MRI of the sciatic and tibial nerves, including MRN and DTI, was prospectively performed in 15 CMT1A patients and 30 healthy controls (HCs). The following MRI parameters were evaluated and correlated with clinical and neurophysiological findings: T2-relaxation time, proton spin density (PD) and DTI (fractional anisotropy [FA] and apparent diffusion coefficient [ADC]).

RESULTS

DTI showed lower FA and higher ADC in CMT1A compared with HCs. T2 relaxation time showed no difference; however, PD of the sciatic nerve was higher in CMT1A. There were some close associations between neuropathy severity and MRN-DTI, with the closest correlation between FA and nerve conduction velocity in the sciatic nerve (r = 0.76, P < 0.01).

DISCUSSION

MRN-DTI evaluation of sciatic and tibial nerves improves the detection of nerve abnormalities in patients with CMT1A. Muscle Nerve 56: E78-E84, 2017.

Pmp22 mutant allele-specific siRNA alleviates demyelinating neuropathic phenotype in vivo

Charcot-Marie-Tooth disease (CMT) is a genetic disorder that can be caused by aberrations in >80 genes. CMT has heterogeneous modes of inheritance, including autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Over 95% of cases are dominantly inherited. In this study, we investigated whether regulation of a mutant allele by an allele-specific small interfering RNA (siRNA) can alleviate the demyelinating neuropathic phenotype of CMT. We designed 19 different allele-specific siRNAs for Trembler J (Tr-J) mice harboring a naturally occurring mutation (Leu16Pro) in Pmp22. Using a luciferase assay, we identified an siRNA that specifically and selectively reduced the expression level of the mutant allele and reversed the low viability of Schwann cells caused by mutant Pmp22 over-expression in vitro. The in vivo efficacy of the allele-specific siRNA was assessed by its intraperitoneal injection to postnatal day 6 of Tr-J mice. Administration of the allele-specific siRNA to Tr-J mice significantly enhanced motor function and muscle volume, as assessed by the rotarod test and magnetic resonance imaging analysis, respectively. Increases in motor nerve conduction velocity and compound muscle action potentials were also observed in the treated mice. In addition, myelination, as evidenced by toluidine blue staining and electron microscopy, was augmented in the sciatic nerves of the mice after allele-specific siRNA treatment. After validating suppression of the Pmp22 mutant allele at the mRNA level in the Schwann cells of Tr-J mice, we observed increased expression levels of myelinating proteins such as myelin basic protein and myelin protein zero. These data indicate that selective suppression of the Pmp22 mutant allele by non-viral delivery of siRNA alleviates the demyelinating neuropathic phenotypes of CMT in vivo, implicating allele-specific siRNA treatment as a potent therapeutic strategy for dominantly inherited peripheral neuropathies.

Charcot-Marie-Tooth 1A: A narrative review with clinical and anatomical perspectives

Charcot-Marie-Tooth 1A (CMT1A) is regarded as the most common hereditary peripheral neurodegenerative disorder. This narrative review highlights perspectives around the historically well-established and characteristic anatomical manifestations of CMT1A seen in the feet, legs and hands, in addition to a clinical diagnosis that may be confirmed by electrophysiology, genetic or molecular markers together with the presence of a typical family history. A less well-known perspective is the potential for systemic manifestations and wider complication. The condition is characterised by a progressive clinical picture with unmistakable anatomical and neurological features that have been described since the late 19th century. There remains no cure although supportive, rehabilitative, and surgical regimes may provide helpful management or amelioration of symptoms. Most recently, the emergence of a pleotherapeutic approach suggests distinct promise. Future research focused on a detailed elucidation of the underlying molecular mechanisms underpinning myelin and axonal function may eventually hold the key to successful treatment of CMT1A. Genetic modification would potentially present a cure. Clin. Anat. 29:547-554, 2016. © 2015 Wiley Periodicals, Inc.

Mutations in the MORC2 gene cause axonal Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT) is a complex disorder with wide genetic heterogeneity. Here we present a new axonal Charcot-Marie-Tooth disease form, associated with the gene microrchidia family CW-type zinc finger 2 (MORC2). Whole-exome sequencing in a family with autosomal dominant segregation identified the novel MORC2 p.R190W change in four patients. Further mutational screening in our axonal Charcot-Marie-Tooth disease clinical series detected two additional sporadic cases, one patient who also carried the same MORC2 p.R190W mutation and another patient that harboured a MORC2 p.S25L mutation. Genetic and in silico studies strongly supported the pathogenicity of these sequence variants. The phenotype was variable and included patients with congenital or infantile onset, as well as others whose symptoms started in the second decade. The patients with early onset developed a spinal muscular atrophy-like picture, whereas in the later onset cases, the initial symptoms were cramps, distal weakness and sensory impairment. Weakness and atrophy progressed in a random and asymmetric fashion and involved limb girdle muscles, leading to a severe incapacity in adulthood. Sensory loss was always prominent and proportional to disease severity. Electrophysiological studies were consistent with an asymmetric axonal motor and sensory neuropathy, while fasciculations and myokymia were recorded rather frequently by needle electromyography. Sural nerve biopsy revealed pronounced multifocal depletion of myelinated fibres with some regenerative clusters and occasional small onion bulbs. Morc2 is expressed in both axons and Schwann cells of mouse peripheral nerve. Different roles in biological processes have been described for MORC2. As the silencing of Charcot-Marie-Tooth disease genes have been associated with DNA damage response, it is tempting to speculate that a deregulation of this pathway may be linked to the axonal degeneration observed in MORC2 neuropathy, thus adding a new pathogenic mechanism to the long list of causes of Charcot-Marie-Tooth disease.

A novel homozygous MPV17 mutation in two families with axonal sensorimotor polyneuropathy

Background

Mutations in MPV17 cause the autosomal recessive disorder mitochondrial DNA depletion syndrome 6 (MTDPS6), also called Navajo neurohepatopathy (NNH). Clinical features of MTDPS6 is infantile onset of progressive liver failure with seldom development of progressive neurologic involvement.

Methods

Whole exome sequencing (WES) was performed to isolate the causative gene of two unrelated neuropathy patients (9 and 13 years of age) with onset of the syndrome. Clinical assessments and biochemical analysis were performed.

Results

A novel homozygous mutation (p.R41Q) in MPV17 was found by WES in both patients. Both showed axonal sensorimotor polyneuropathy without liver and brain involvement, which is neurophysiologically similar to axonal Charcot-Marie-Tooth disease (CMT). A distal sural nerve biopsy showed an almost complete loss of the large and medium-sized myelinated fibers compatible with axonal neuropathy. An in vitro assay using mouse motor neuronal cells demonstrated that the abrogation of MPV17 significantly affected cell integrity. In addition, the expression of the mutant protein affected cell proliferation. These results imply that both the loss of normal function of MPV17 and the gain of detrimental effects of the mutant protein might affect neuronal function.

Conclusion

We report a novel homozygous mutation in MPV17 from two unrelated patients harboring axonal sensorimotor polyneuropathy without hepatoencephalopathy. This report expands the clinical spectrum of diseases caused by mutations of MPV17, and we recommend MPV17 gene screening for axonal peripheral neuropathies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-015-0430-1) contains supplementary material, which is available to authorized users.

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.

MR Imaging of the Lumbosacral Plexus: A Review of Techniques and Pathologies

The lumbosacral plexus is a complex anatomic area that serves as the conduit of innervation and sensory information to and from the lower extremities. It is formed by the ventral rami of the lumbar and sacral spine which then combine into larger nerves serving the pelvis and lower extremities. It can be a source of severe disability and morbidity for patients when afflicted with pathology. Patients may experience motor weakness, sensory loss, and/or debilitating pain. Primary neurologic processes can affect the lumbosacral plexus in both genetic and acquired conditions and typically affect the plexus and nerves symmetrically. Additionally, its unique relationship to the pelvic musculature and viscera render it vulnerable to trauma, infection, and malignancy. Such conditions are typically proceeded by a known history of trauma or established pelvic malignancy or infection. Magnetic resonance imaging is an invaluable tool for evaluation of the lumbosacral plexus due to its anatomic detail and sensitivity to pathologic changes. It can identify the cause for disability, indicate prognosis for improvement, and be a tool for delivery of interventions. Knowledge of proper MR protocols and imaging features is key for appropriate and timely diagnosis. Here we discuss the relevant anatomy of the lumbosacral plexus, appropriate imaging techniques for its evaluation, and discuss the variety of pathologies that may afflict it.

NEFL E396K mutation is associated with a novel dominant intermediate Charcot-Marie-Tooth disease phenotype

The purpose of the study was to describe a pedigree with NEFL E396K mutation associated with a novel dominant intermediate Charcot-Marie-Tooth disease (DI-CMT) phenotype. The pedigree comprised four patients over two generations, aged between 35 and 59 years, who have been serially evaluated since 1993. Their clinical picture was characterized by pes cavus, sensorimotor neuropathy and spastic gait. Both older patients showed ascending leg weakness to involve pelvic musculature. CMT neuropathy score ranged from 14 to 26 (moderate to severe disease). Electrophysiology showed uniform nerve conduction slowing in the intermediate range, both in distal and proximal nerve segments. Multimodal evoked potential and blink reflex studies revealed abnormalities indicative of central sensorimotor pathway dysfunction. On imaging studies of lower-limb musculature, there was massive atrophy of intrinsic foot muscles and to a lesser degree of calves and thighs predominating in muscles innervated by tibial and sciatic nerves. In both patients exhibiting waddling gait, there was atrophy of pelvic muscles mainly involving gluteus medius, gluteus minimus and piriformis. We conclude that NEFL E396K mutation may manifest with a novel DI-CMT phenotype, characterized by simultaneous involvement of the peripheral and central nervous system.

Proximal nerve magnetization transfer MRI relates to disability in Charcot-Marie-Tooth diseases

OBJECTIVE

The objectives of this study were (1) to develop a novel magnetization transfer ratio (MTR) MRI assay of the proximal sciatic nerve (SN), which is inaccessible via current tools for assessing peripheral nerves, and (2) to evaluate the resulting MTR values as a potential biomarker of myelin content changes in patients with Charcot-Marie-Tooth (CMT) diseases.

METHODS

MTR was measured in the SN of patients with CMT type 1A (CMT1A, n = 10), CMT type 2A (CMT2A, n = 3), hereditary neuropathy with liability to pressure palsies (n = 3), and healthy controls (n = 21). Additional patients without a genetically confirmed subtype (n = 4), but whose family histories and electrophysiologic tests were consistent with CMT, were also included. The relationship between MTR and clinical neuropathy scores was assessed, and the interscan and inter-rater reliability of MTR was estimated.

RESULTS

Mean volumetric MTR values were significantly decreased in the SN of patients with CMT1A (33.8 ± 3.3 percent units) and CMT2A (31.5 ± 1.9 percent units) relative to controls (37.2 ± 2.3 percent units). A significant relationship between MTR and disability scores was also detected (p = 0.01 for genetically confirmed patients only, p = 0.04 for all patients). From interscan and inter-rater reliability analyses, proximal nerve MTR values were repeatable at the slicewise and mean volumetric levels.

CONCLUSIONS

MTR measurements may be a viable biomarker of proximal nerve pathology in patients with CMT.

Muscle MRI in patients with long-chain fatty acid oxidation disorders

INTRODUCTION

Muscle magnetic resonance imaging (MRI) is a useful tool for visualizing abnormalities in neuromuscular disorders. The value of muscle MRI has not been studied in long-chain fatty acid oxidation (lcFAO) disorders. LcFAO disorders may present with metabolic myopathy including episodic rhabdomyolysis.

OBJECTIVE

To investigate whether lcFAO disorders are associated with muscle MRI abnormalities.

METHODS

Lower body MRI was performed in 20 patients with lcFAO disorders, i.e. three carnitine palmitoyltransferase 2 deficiency (CPT2D), 12 very long-chain acyl-CoA dehydrogenase deficiency (VLCADD), three mitochondrial trifunctional protein deficiency (MTPD) and two isolated long-chain hydroxyacyl-CoA dehydrogenase deficiency (LCHADD).

RESULTS

At the time of MRI, four patients had muscle weakness, 14 had muscle pain and 13 were exercise intolerant. Median creatine kinase (CK) level of patients at the day of MRI was 398 U/L (range 35-12,483). T1W and STIR signal intensity (SI) were markedly increased in MTPD patients from girdle to lower leg. VLCADD patients showed predominantly proximal T1W SI changes, whereas LCHADD patients mostly showed distal T1W SI changes. Prominent STIR weighted signal intensity increases of almost all muscle groups were observed in patients with VLCADD and LCHADD with very high CK (>11.000) levels.

CONCLUSIONS AND RELEVANCE

lcFAO disorders are associated with specific patterns of increased T1W and STIR signal intensity. These patterns may reflect lipid accumulation and inflammation secondary to lcFAO defects and progressive muscle damage. Future studies are needed to investigate whether muscle MRI might be a useful tool to monitor disease course and to study pathogenesis of lcFAO related myopathy.

Reproducibility, and age, body-weight and gender dependency of candidate skeletal muscle MRI outcome measures in healthy volunteers

Objectives

Quantitative magnetic resonance imaging (MRI) can potentially meet the pressing need for objective, sensitive, reproducible outcome measures in neuromuscular disease trials. We tested, in healthy volunteers, the consistency, reliability and sensitivity to normal inter-subject variation of MRI methods targeted to lower limb muscle pathology to inform the design of practical but comprehensive MRI outcome measure protocols for use in imminent patient studies.

Methods

Forty-seven healthy volunteers, age 21-81 years, were subject at 3T to three-point Dixon fat-fraction measurement, T₁-relaxometry, T₂-relaxometry and magnetisation transfer ratio (MTR) imaging at mid-thigh and mid-calf level bilaterally. Fifteen subjects underwent repeat imaging at 2 weeks.

Results

Mean between-muscle fat fraction and T₂ differences were small, but significant (p < 0.001). Fat fraction and T₂ correlated positively, and MTR negatively with subject age in both the thigh and calf, with similar significant correlations with weight at thigh level only (p < 0.001 to p < 0.05). Scan-rescan and inter-observer intra-class correlation coefficients ranged between 0.62-0.84 and 0.79-0.99 respectively.

Conclusions

Quantitative lower-limb muscle MRI using readily implementable methods was sensitive enough to demonstrate inter-muscle differences (small in health), and correlations with subject age and weight. In combination with high reliability, this strongly supports the suitability of these methods to provide longitudinal outcome measures in neuromuscular disease treatment trials.

Key points

• Quantitative lower limb muscle MRI provides potential outcome measures in neuromuscular diseases

• Bilateral thigh/calf coverage using sequences sensitive to acute and chronic pathology

• Measurements have excellent scan-rescan and interobserver reliability

• Measurements show small but significant inter-subject age and weight dependency

• Readily implementable sequences suitable for further assessment in patient studies

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-014-3145-6) contains supplementary material, which is available to authorized users.

Evolution of Charcot-Marie-Tooth disease type 1A duplication: a 2-year clinico-electrophysiological and lower-limb muscle MRI longitudinal study

The objective of this study was to analyze Charcot-Marie-Tooth disease type 1A (CMT1A) evolution. We conducted a 2-year longitudinal study in 14 CMT1A patients and 14 age- and sex-matched controls. In the patients, we performed neurological examination with hand-held dynamometry, electrophysiology, and lower-limb muscle MRI, both at baseline and 2 years later, while controls were examined at baseline only. Patients' ages ranged from 12 to 51 years. Outstanding manifestations on initial evaluation included pes cavus, areflexia, lower-limb weakness, and foot hypopallesthesia. In evaluating muscle power, good correlation was observed between manual testing and dynamometry. Compared to controls, Lunge, 10-Meter-Walking, and 9-Hole-Peg tests were impaired. Their CMT neuropathy score and functional disability scale showed that patients exhibited mild phenotype and at most slight walking difficulty. Electrophysiology revealed marked nerve conduction slowing and variable compound muscle action potential amplitude reduction. On lower-limb muscle MRI, there was distally accentuated fatty infiltration accompanied by edema in calf muscles. All these clinico-electrophysiological and imaging findings remained almost unaltered during monitoring. Using multivariate analysis, no significant predictors of progression associated to the disease were obtained. We conclude that in the 2-year period of study, CMT1A patients showed mild progression with good concordance between clinico-electrophysiological and imaging findings.