Early onset Charcot‐Marie‐Tooth neuropathy type 2A and severe developmental delay: expanding the clinical phenotype of MFN2‐related neuropathy

Charcot‐Marie‐Tooth (CMT) syndromes are a group of clinically heterogeneous disorders of the peripheral nervous system. Mutations of mitofusin 2 (MFN2) have been recognized to be associated with CMT type 2A (CMT2A). CMT2A is primarily an axonal disorder resulting in motor and sensory neuropathy. We report a male child with psychomotor delay, dysmorphic features, and weakness of lower limbs associated with electrophysiological features of severe, sensory‐motor, axonal neuropathy. The patient was diagnosed with early onset CMT2A and severe psychomotor retardation associated with c.310C>T mutation (p.R104W) in MFN2 gene. CMT2A should be considered in patients with both axonal sensory‐motor neuropathy and developmental delay.     

Diabetes mellitus exacerbates motor and sensory impairment in CMT1A

Abstract Charcot‐Marie‐Tooth disease type 1A (CMT1A) is caused by a duplication of PMP22 on chromosome 17 and is the most commonly inherited demyelinating neuropathy. Diabetes frequently causes predominantly sensory neuropathy. Whether diabetes exacerbates CMT1A is unknown. We identified 10 patients with CMT1A and diabetes and compared their impairment with 48 age‐matched control patients with CMT1A alone. Comparisons were made with the Charcot‐Marie‐Tooth disease (CMT) neuropathy score (CMTNS) and by electrophysiology. The CMTNS was significantly higher in patients with diabetes (20.25 ± 2.35) compared with controls (15.19 ± 0.69; p = 0.01). Values were particularly higher for motor signs and symptoms. Seven of the 10 diabetic patients had CMTNS >20 (severe CMT), while only 7 of the 48 age‐matched controls had scores >20. There was a trend for CMT1A patients with diabetes to have low compound muscle action potentials and sensory nerve action potentials, although nerve conduction velocities were not slower in diabetic patients compared with controls. Diabetes was associated with more severe motor and sensory impairment in patients with CMT1A.     

Spinal charcot‐marie‐tooth disease: A reappraisal

Introduction: Distal hereditary motor neuropathy (dHMN) is characterized by isolated distal muscle atrophy without sensory deficit. Nevertheless, clinical sensory loss has been reported despite preserved sensory nerve conduction in a few patients, thus differentiating these cases from the classical type 2 Charcot‐Marie‐Tooth disease (CMT2). Methods: We report 4 patients who presented with clinical sensory and motor neuropathy and normal peripheral sensory nerve conduction studies and were investigated with complete electrophysiological studies, including somatosensory evoked potentials (SEP). Results: These patients had a clinical presentation of classical CMT with isolated axonal motor neuropathy suggestive of dHMN. Interestingly, tibial nerve SEPs showed abnormalities suggestive of proximal involvement of dorsal roots that may explain the clinical somatosensory disturbances. Conclusions: These cases support the concept of spinal CMT that should be recognized as an intermediate form between dHMN and CMT2. SEP recording was helpful in defining a more precise phenotype of spinal CMT. Muscle Nerve 46: 603–607, 2012     

Late‐onset hereditary sensory and autonomic neuropathy expands the phenotypic spectrum of MFN2‐related diseases

Mutations in the Mitofusin 2 (MFN2) gene have been identified in patients with autosomal dominant axonal motor and sensory neuropathy or Charcot–Marie‐Tooth 2A (CMT2A). Here we describe clinical and pathological changes in an adult patient with sporadic hereditary sensory and autonomic neuropathy (HSAN) due to an MFN2 mutation. The patient was a 53‐year‐old man who had sensory involvement and anhidrosis in all limbs without motor features. The electrophysiological assessment documented severe axonal sensory neuropathy. The sural nerve biopsy confirmed the electrophysiological findings, revealing severe loss of myelinated and unmyelinated fibers with regeneration clusters. Genetic analysis revealed the previously identified mutation c.776 G > A in MFN2. Our report expands the phenotypic spectrum of MFN2‐related diseases. Sequencing of MFN2 should be considered in all patients presenting with late‐onset HSAN.     

Exome sequencing reveals mutations in MFN2 and GDAP1 in severe Charcot–Marie–Tooth disease

The aim of our study was to characterize electrophysiologically and explain the genetic cause of severe Charcot–Marie–Tooth (CMT) in a 3.5‐year‐old with asymptomatic parents and a maternal grandfather with a history of mild adult‐onset axonal neuropathy. Severity of neuropathy was assessed by Charcot–Marie–Tooth neuropathy score (CMTNS). Whole‐exome sequencing was performed using an Illumina TruSeq Exome Enrichment Kit on the HiSeq 1500 with results followed up by Sanger sequencing on an ABI Prism 3500XL (Applied Biosystems, Foster City, CA, USA). Paternity was confirmed using a panel of 15 hypervariable markers. Electrophysiological studies demonstrated severe axonal sensory‐motor neuropathy in the proband, mild motor neuropathy in his mother, and mild sensory‐motor neuropathy in his grandfather. CMTNS in the proband, his mother, and grandfather was 21, 1, and 12, respectively. On genetic analysis, the boy was found to carry a heterozygous dominant MFN2 T236M mutation transmitted via the maternal line and a de novo GDAP1 H123R mutation. Our findings emphasize the need to search for more than one causative mutation when significant intrafamilial variability of CMT phenotype occurs and underline the role of whole‐exome sequencing in the diagnosis of compound forms of CMT disease.     

A novel p.Glu175X premature stop mutation in the C-terminal end of HSP27 is a cause of CMT2

Mutations in the gene HSPB1, encoding the small heat shock protein 27 (HSP27), are a cause of distal hereditary motor neuropathy (dHMN) and axonal Charcot-Marie-Tooth disease (CMT2). dHMN and CMT2 are differentiated by the presence of a sensory neuropathy in the latter although in the case of HSPB1 this division is artificial as CMT2 secondary to HSPB1 mutations is predominantly a motor neuropathy with only minimal sensory involvement. A recent study in mice has suggested that mutations in the C-terminus result in a motor only phenotype resembling dHMN, whereas mutations at the N-terminus result in a CMT2-like phenotype. However, we present a family with a novel mutation in the C-terminus of HSP27 (p.Glu175X) with a motor predominant distal neuropathy but with definite sensory involvement compatible with CMT2. This case highlights the artificial distinction between patients with motor predominant forms of CMT2 and dHMN and argues against the hypothesis that mutations in the C-terminus have no sensory involvement.     

A novel NDRG1 mutation in a non‐Romani patient with CMT4D/HMSN‐Lom

Charcot‐Marie‐Tooth disease type 4D (CMT4D), also known as hereditary motor and sensory neuropathy Lom type (HMSNL), is an autosomal recessive, early onset, severe demyelinating neuropathy with hearing loss, caused by N‐Myc downstream‐regulated gene 1 (NDRG1) mutations. CMT4D is rare with only three known mutations, one of which (p.Arg148Ter) is found in patients of Romani ancestry and accounts for the vast majority of cases. We report a 38‐year‐old Italian female with motor development delay, progressive neuropathy, and sensorineural deafness. Magnetic resonance imaging showed slight atrophy of cerebellum, medulla oblongata, and upper cervical spinal cord. She had a novel homozygous NDRG1 frameshift mutation (c.739delC; p.His247ThrfsTer74). The identification of this NDRG1 mutation confirms that CMT4D is not a private Romani disease and should be considered in the differential diagnosis of recessive demyelinating CMT.     

Coexistence of Charcot‐Marie‐Tooth disease type 1A and anti‐MAG neuropathy

At age 35, a man with a genetic diagnosis of Charcot‐Marie‐Tooth disease type 1A (CMT1A) but no family history of neuropathy and no clinical symptoms developed rapidly progressive loss of balance, distal limb numbness, loss of manual dexterity, and hand tremor. Five years later, he walked with support and had mild pes cavus, marked sensory ataxia, severe leg and hand weakness, absent deep tendon reflexes (DTRs), severe sensory loss, and hand tremor. He had dramatically reduced motor nerve conduction velocity (MNCV), strikingly prolonged motor distal latencies, absent sensory action potentials and lower limb compound muscle action potentials. CMT1A duplication was reconfirmed but the dramatic change in his clinical course suggested a superimposed acquired neuropathy. An IgM‐kappa monoclonal gammopathy of uncertain significance (MGUS) with high titer anti‐myelin associated glycoprotein (anti‐MAG) activity was found. Nerve biopsy showed severe loss of myelinated fibers with onion bulbs, no evidence of uncompacted myelin, and few IgM deposits. Rituximab was given and he improved. It is very likely that this is a chance association of two rare and slowly progressive neuropathies; rapidly worsening course may have been due to a “double hit”. Interestingly, there are reports of possible superimposition of dysimmune neuropathies on hereditary ones, and the influence of the immune system on inherited neuropathies is matter for debate.     

Rigid spine syndrome associated with sensory‐motor axonal neuropathy resembling Charcot–Marie‐Tooth disease is characteristic of Bcl‐2‐associated athanogene‐3 gene mutations even without cardiac involvement

Introduction: Bcl‐2‐associated athanogene‐3 (BAG3) mutations have been described in rare cases of rapidly progressive myofibrillar myopathies. Symptoms begin in the first decade with axial involvement and contractures and are associated with cardiac and respiratory impairment in the second decade. Axonal neuropathy has been documented but usually not as a key clinical feature. Methods: We report a 24‐year‐old woman with severe rigid spine syndrome and sensory‐motor neuropathy resembling Charcot–Marie–Tooth disease (CMT). Results: Muscle MRI showed severe fat infiltration without any specific pattern. Deltoid muscle biopsy showed neurogenic changes and discrete myofibrillar abnormalities. Electrocardiogram and transthoracic echocardiography results were normal. Genetic analysis of a panel of 45 CMT genes showed no mutation. BAG3 gene screening identified the previously reported c.626C>T, pPro209Leu, mutation. Discussion: This case indicates that rigid spine syndrome and sensory‐motor axonal neuropathy are key clinical features of BAG3 mutations that should be considered even without cardiac involvement. Muscle Nerve, 57 : 330–334, 2018     

Neurofilament light mutation causes hereditary motor and sensory neuropathy with pyramidal signs

To identify novel mutations causing hereditary motor and sensory neuropathy (HMSN) with pyramidal signs, a variant of Charcot‐Marie‐Tooth disease (CMT), we screened 28 CMT and related genes in four members of an affected Japanese family. Clinical features included weakness of distal lower limb muscles, foot deformity, and mild sensory loss, then late onset of progressive spasticity. Electrophysiological studies revealed widespread neuropathy. Electron microscopic analysis showed abnormal mitochondria and mitochondrial accumulation in the neurons and Schwann cells. Brain magnetic resonance imaging (MRI) revealed an abnormally thin corpus callosum. In all four, microarrays detected a novel heterozygous missense mutation c.1166A>G (p.Y389C) in the gene encoding the light‐chain neurofilament protein (NEFL), indicating that NEFL mutations can result in a HMSN with pyramidal signs phenotype.     

Clinical and genetic features of Charcot‐Marie‐Tooth disease 2F and hereditary motor neuropathy 2B in Japan

Mutations in small heat shock protein beta‐1 (HspB1) have been linked to Charcot‐Marie‐Tooth (CMT) disease type 2F and distal hereditary motor neuropathy type 2B. Only four cases with HSPB1 mutations have been reported to date in Japan. In this study between April 2007 and October 2014, we conducted gene panel sequencing in a case series of 1,030 patients with inherited peripheral neuropathies (IPNs) using DNA microarray, targeted resequencing, and whole‐exome sequencing. We identified HSPB1 variants in 1.3% (13 of 1,030) of the patients with IPNs, who exhibited a male predominance. Based on neurological and electrophysiological findings, seven patients were diagnosed with CMT disease type 2F, whereas the remaining six patients were diagnosed with distal hereditary motor neuropathy type 2B. P39L, R127W, S135C, R140G, K141Q, T151I, and P182A mutations identified in 12 patients were described previously, whereas a novel K123* variant with unknown significance was found in 1 patient. Diabetes and impaired glucose tolerance were detected in 6 of the 13 patients. Our findings suggest that HSPB1 mutations result in two phenotypes of inherited neuropathies and extend the phenotypic spectrum of HSPB1‐related disorders.     

A novel mutation of LRSAM1 in a Chinese family with Charcot‐Marie‐Tooth disease

Charcot‐Marie‐Tooth (CMT) disease is the most common inherited peripheral neuropathy characterized by progressive distal muscle weakness and atrophy with decreased or absent tendon reflexes. Mutations in LRSAM1 have been identified to cause CMT disease type 2P. We report a novel LRSAM1 mutation c.2021‐2024del (p.E674VfsX11) in a Chinese autosomal dominant CMT disease type 2 family. The phenotype was characterized by late onset and mild sensory impairment. Electrophysiological findings showed normal or mildly to moderately reduced motor and sensory nerve conduction velocities in lower and upper limb nerves.     

A novel pathogenic variant of NEFL responsible for deafness associated with peripheral neuropathy discovered through next‐generation sequencing and review of the literature

Neurofilaments are neuron‐specific intermediate filaments essential for the radial growth of axons during development and the maintenance of axonal diameter. Pathogenic variants of Neurofilament Light (NEFL) are associated with CMT1F, CMT2E, and CMTDIG and have been observed in less than 1% of Charcot‐Marie‐Tooth (CMT) cases, resulting in the reporting of 35 variants in 173 CMT patients to date. However, only six variants have been reported in 17 patients with impaired hearing. No genotype‐phenotype correlations have yet been established. Here, we report an additional case: a 69‐year‐old female, who originally presented with axonal sensory and motor neuropathy at the age of 45, associated with moderate sensorineural hearing loss, with a slight slope at high frequencies. Next‐generation sequencing identified a novel pathogenic variant: c.269A > G, p.(Glu90Gly). Hearing impairment is often linked to CMT due to pathogenic variants of NEFL, especially p.(Glu90Lys) and p.(Asn98Ser), and in our case p.(Glu90Gly). These pathogenic variants are all located at hot spots, in the head domain and the two ends of the rod domain of the protein.     

Clinical and genetic spectra of Charcot‐Marie‐Tooth disease in Chinese Han patients

Charcot‐Marie‐Tooth disease (CMT) is a common hereditary motor and sensory neuropathy. Epidemiological data for Chinese CMT patients are few. This study aimed to analyze the electrophysiological and genetic characteristics of Chinese Han patients. A total of 106 unrelated patients with the clinical diagnosis of CMT were included. Clinical examination, nerve conduction studies (NCS), next‐generation sequencing (NGS), and bioinformatic analyses were performed. Genetic testing was performed for 82 patients; 27 (33%) patients carried known CMT‐associated gene mutations. PMP22 duplication was detected in 10 (12%) patients and GJB1 mutations in 9 (11%) patients. The mutation rate was higher in patients with a positive family history than in the sporadic cases (50% vs. 27%, p < 0.05). Six novel CMT‐associated gene mutations including BSCL2 (c.461C>T), LITAF (c.32C>G), MFN2 (c.497C>T), GARS (c.794C>T), NEFL (c.280C>T), and MPZ (c.440T>C) were discovered. All except the LITAF (c.32C>G) mutation were identified as “disease causing” via bioinformatic analyses. In this Chinese Han population, the frequency of PMP22 gene duplication in those with CMT1 was slightly (50% vs. 70%–80%) less than in Western/Caucasian populations. The novel CMT‐associated gene mutations broaden the mutation diversity of CMT1. NGS should be considered for genetic analyses in CMT patients.     

Mutational mechanisms in MFN2‐related neuropathy: compound heterozygosity for recessive and semidominant mutations

Mitofusin‐2 (MFN2) mutations are the most common cause of autosomal dominant axonal Charcot‐Marie‐Tooth disease (CMT, type 2A), sometimes complicated by additional features such as optic atrophy (CMT6) and upper motor neuron involvement (CMT5). Several pathogenic mutations are reported, mainly acting in a dominant fashion, although few sequence variants behaved as recessive or semidominant in rare homozygous or compound heterozygous patients. We describe a 49‐year‐old woman with CMT5 associated with compound heterozygosity for two MFN2 variants, one already reported missense mutation (c.748C>T, p.R250W) and a novel nonsense sequence change (c.1426C>T, p.R476*). Her mother, carrying the p.R250W variant, had very late‐onset minimal axonal neuropathy, whilst the father harboring the nonsense sequence change had neither clinical nor electrophysiological neuropathy. The missense mutation is likely pathogenic according to in silico analyses and a previous report, while the nonsense variant is predicted to behave as a null allele. The p.R250W variant behaves as semidominant by causing only a mild, almost subclinical, neuropathy when heterozygous; the nonsense mutation in the father was phenotypically silent, suggesting that haploinsufficiency for MFN2 is not disease causative, but was deleterious in the daughter who had only one active mutated MFN2 allele.     

Clinical features of inherited neuropathy with BSCL2 mutations in Japan

Heterozygous mutations in the Berardinelli‐Seip congenital lipodystrophy 2 (BSCL2) gene have been reported with different clinical phenotypes including Silver syndrome (SS)/spastic paraplegia 17 (SPG17), distal hereditary motor neuropathy type V (dHMN‐V), and Charcot‐Marie‐Tooth (CMT) disease type 2. We screened 407 Japanese patients who were clinically suspected of having CMT by exome sequencing and searched mutations in BSCL2. As a result, we identified five patients with heterozygous mutations in BSCL2. We confirmed three cases of known mutations (p.N88S and p.S90L) and two cases of novel mutations (p.N88T and p.S141A). The clinical features of the cases with known mutations in Japan were similar to those previously reported in other countries. In particular, there were many cases with sensory disturbance. The case with p.N88T mutation showed severe phenotype such as early onset age and prominent vocal cord paresis. The case with p.S141A mutation showed characteristics of demyelinating neuropathy such as CMT disease type 1 by electrophysiological examination. In this article, we report the clinical features and spread of cases with BSCL2 mutation in a Japanese cohort.     

A case of peripheral nerve microvasculitis associated with multiple myeloma and bortezomib treatment

Introduction: Bortezomib‐induced peripheral neuropathy typically presents as a painful, length‐dependent sensory predominant neuropathy. Methods: A case report, including nerve pathology, is presented of a man with multiple myeloma who developed a severe motor predominant polyradiculoneuropathy in the setting of bortezomib treatment. We also review the Mayo Clinic Hematology Dysproteinemia database for patients treated with bortezomib. Results: A 53‐year‐old man with Stage III multiple myeloma developed a severe motor predominant polyradiculoneuropathy following bortezomib treatment with electrophysiological features of multiple conduction blocks and pathological evidence of peripheral nerve microvasculitis. Our institutional experience is that 36.5% of dysproteinemia patients treated with bortezomib develop treatment‐emergent peripheral neuropathy, and the most common pattern is a painful sensory predominant peripheral neuropathy. Conclusions: A motor predominant polyradiculoneuropathy is a rare presentation of bortezomib‐associated peripheral neuropathy in multiple myeloma patients which may progress despite treatment withdrawal and may be due to microvasculitis. Muscle Nerve, 2012     

Clinical spectrum of AIFM1‐associated disease in an Irish family,from mild neuropathy to severe cerebellar ataxia with colour blindness

Mutations in apoptosis‐inducing factor mitochondrion‐associated‐1 (AIFM1) cause X‐linked peripheral neuropathy (Cowchock syndrome, CMT4X); however, more recently a cerebellar presentation has been described. We describe a large Irish family with seven affected males. They presented with a variable age of onset, 18 months to 39 years of age. All developed variably present sensorineural deafness, peripheral neuropathy, cerebellar ataxia, and pyramidal involvement. In addition, three had colour vision deficiency. Scale for the assessment and rating of ataxia ranged 2 to 23/40, while Charcot‐Marie‐Tooth neuropathy score 2 varied between 7 and 13/36. All individuals had normal cognitive assessment. Neurophysiology demonstrated length‐dependent large‐fibre sensorimotor axonal neuropathy, with particular involvement of superficial radial sensory responses. Brain imaging, performed in four, revealed varying extent of cerebellar atrophy, and white matter changes in one. Optical coherence tomography was abnormal in one, who had unrelated eye pathology. Four obligate female carriers were assessed clinically, two of them neurophysiologically; all were unaffected. Whole genome sequencing demonstrated a previously reported hemizygous AIFM1 mutation. Analysis for mutations in other genes associated with colour deficiency was negative. AIFM1‐associated phenotype in this family demonstrated significant variability. To our knowledge, this is the first report of AIFM1‐associated colour blindness. Superficial radial nerve was particularly affected neurophysiologically, which could represent a phenotypic marker towards this specific genetic diagnosis.     

Phrenic nerve involvement and respiratory muscle weakness in patients with Charcot‐Marie‐Tooth disease 1A

Diaphragm weakness in Charcot‐Marie‐Tooth disease 1A (CMT1A) is usually associated with severe disease manifestation. This study comprehensively investigated phrenic nerve conductivity, inspiratory and expiratory muscle function in ambulatory CMT1A patients. Nineteen adults with CMT1A (13 females, 47 ± 12 years) underwent spiromanometry, diaphragm ultrasound, and magnetic stimulation of the phrenic nerves and the lower thoracic nerve roots, with recording of diaphragm compound muscle action potentials (dCMAP, n = 15), transdiaphragmatic and gastric pressures (twPdi and twPgas, n = 12). Diaphragm motor evoked potentials (dMEP, n = 15) were recorded following cortical magnetic stimulation. Patients had not been selected for respiratory complaints. Disease severity was assessed using the CMT Neuropathy Scale version 2 (CMT‐NSv2). Healthy control subjects were matched for age, sex, and body mass index. The following parameters were significantly lower in CMT1A patients than in controls (all P < .05): forced vital capacity (91 ± 16 vs 110 ± 15% predicted), maximum inspiratory pressure (68 ± 22 vs 88 ± 29 cmH₂O), maximum expiratory pressure (91 ± 23 vs 123 ± 24 cmH₂O), and peak cough flow (377 ± 135 vs 492 ± 130 L/min). In CMT1A patients, dMEP and dCMAP were delayed. Patients vs controls showed lower diaphragm excursion (5 ± 2 vs 8 ± 2 cm), diaphragm thickening ratio (DTR, 1.9 [1.6‐2.2] vs 2.5 [2.1‐3.1]), and twPdi (8 ± 6 vs 19 ± 7 cmH₂O; all P < .05). DTR inversely correlated with the CMT‐NSv2 score (r = ?.59, P = .02). There was no group difference in twPgas following abdominal muscle stimulation. Ambulatory CMT1A patients may show phrenic nerve involvement and reduced respiratory muscle strength. Respiratory muscle weakness can be attributed to diaphragm dysfunction alone. It relates to neurological impairment and likely reflects a disease continuum.