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.     

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.     

Small heat shock protein B3 (HSPB3) mutation in an axonal Charcot‐Marie‐Tooth disease family

Heat shock protein B3 (HSPB3) gene encodes a small heat‐shock protein 27‐like protein which has a high sequence homology with HSPB1. A mutation in the HSPB3 was reported as the putative underlying cause of distal hereditary motor neuropathy 2C (dHMN2C) in 2010. We identified a heterozygous mutation (c.352T>C, p.Tyr118His) in the HSPB3 from a Charcot‐Marie‐Tooth disease type 2 (CMT2) family by the method of targeted next generation sequencing. The mutation was located in the well conserved alpha‐crystalline domain, and several in silico predictions indicated a pathogenic effect of the mutation. Clinical and electrophysiological features of the patients indicated the axonal type of CMT. Clinical symptoms without sensory involvements were similar between the present family and the previous family. Mutations in the HSPB1 and HSPB8 genes have been reported to be relevant with both types of CMT2 and dHMN. Our findings will help in the molecular diagnosis of CMT2 by expanding the phenotypic range due to the HSPB3 mutations.     

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 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.     

Clinical features of a family with late-onset distal hereditary motor neuropathy harboring p.Pro39Leu variant of HSPB1

Background and Aims

Pathogenic variants of HSPB1, the gene encoding the small heat shock protein 27, have been reported to cause autosomal dominant distal hereditary motor neuropathy (dHMN) type II and autosomal dominant Charcot–Marie-Tooth (CMT) disease with minimal sensory involvement (CMT2F). This study aimed to describe the clinical features of patients in a family with late-onset dHMN carrying the Pro39Leu variant of HSPB1.

Methods

Whole-exome sequence analysis identified a heterozygous pathogenic variant (Pro39Leu) of HSPB1 in the proband. The presence of the HSPB1 Pro39Leu variant in two affected individuals was confirmed using direct nucleotide sequence analysis.

Results

Both patients exhibited distal muscle weakness with lower extremity predominance and no obvious sensory deficits, leading to a clinical diagnosis of late-onset dHMN. Nerve conduction studies (NCSs) revealed a subclinical complication of sensory disturbance in one of the patients. The clinical and electrophysiological findings of patients with the HSPB1 Pro39Leu variant in this study and previous reports are summarized.

Interpretation

This study suggests that the clinical spectrum of patients carrying HSPB1 Pro39Leu variants, especially the disease onset, might be broader than expected, and HSPB1 variants should be considered in patients diagnosed with late-onset dHMN. Furthermore, patients with dHMN may have concomitant sensory deficits that should be evaluated using NCSs.     

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.     

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.     

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.     

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.     

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     

Multifocal motor neuropathy with high titers of anti‐MAG antibodies

Multifocal motor neuropathy (MMN) and anti‐myelin‐associated glycoprotein (anti‐MAG)‐associated neuropathy are clinically and electrophysiologically distinct entities. We describe a patient with characteristic features of both neuropathies, raising the possibility of an overlap syndrome. A 49‐year‐old patient reported a history of slowly progressive predominantly distal tetraparesis, with mild sensory deficits. Nerve conduction studies demonstrated persistent motor conduction blocks outside compression sites, typical of MMN. Laboratory findings revealed persistently high titers of anti‐MAG immunoglobulin Mλ (IgMλ) paraprotein in the context of a monoclonal gammapathy of unknown significance. Skin biopsy of distal lower limb revealed IgM positive terminal nerve perineurium deposits. This case suggests that the distinction between subtypes of chronic inflammatory neuropathies may not be as clear as initially thought, and that the pattern of pathogenicity of anti‐MAG antibodies may vary.     

Whole‐exome sequencing reveals a novel missense mutation in the MARS gene related to a rare Charcot‐Marie‐Tooth neuropathy type 2U

Charcot‐Marie‐Tooth (CMT) is a heterogeneous group of progressive disorders, characterized by chronic motor and sensory polyneuropathy. This hereditary disorder is related to numerous genes and varying inheritance patterns. Thus, many patients do not reach a final genetic diagnosis. We describe a 13‐year‐old girl presenting with progressive bilateral leg weakness and gait instability. Extensive laboratory studies and spinal magnetic resonance imaging scan were normal. Nerve conduction studies revealed severe lower limb peripheral neuropathy with prominent demyelinative component. Following presumptive diagnosis of chronic inflammatory demyelinating polyneuropathy, the patient received treatment with steroids and intravenous immunoglobulins courses for several months, with no apparent improvement. Whole‐exome sequencing revealed a novel heterozygous c.2209C>T (p.Arg737Trp) mutation in the MARS gene (OMIM 156560). This gene has recently been related to CMT type 2U. In‐silico prediction programs classified this mutation as a probable cause for protein malfunction. Allele frequency data reported this variant in 0.003% of representative Caucasian population. Family segregation analysis study revealed that the patient had inherited the variant from her 60‐years old mother, reported as healthy. Neurologic examination of the mother demonstrated decreased tendon reflexes, while nerve conduction studies were consistent with demyelinative and axonal sensory‐motor polyneuropathy. Our report highlights the importance of next‐generation sequencing approach to facilitate the proper molecular diagnosis of highly heterogeneous neurologic disorders. Amongst other numerous benefits, this approach might prevent unnecessary diagnostic testing and potentially harmful medical treatment.     

Immunotherapy‐responsive allodynia due to distal acquired demyelinating symmetric (DADS) neuropathy

Introduction: Distal acquired demyelinating symmetric (DADS) neuropathy is a distal variant of chronic inflammatory demyelinating polyradiculoneuropathy. It is characterized by chronic distal symmetric sensory or sensorimotor deficits. Sensory ataxia is a common clinical presentation. Nerve conduction studies typically show markedly prolonged distal motor latencies. Methods: We report 2 patients with chronic progressive generalized pain and fatigue, with normal neurological examinations except for allodynia. Results: Nerve conduction studies were typical of DADS neuropathy. Monoclonal protein studies were negative. Cerebrospinal fluid protein levels were elevated. Sural nerve biopsies revealed segmental demyelination and remyelination. One biopsy had marked endoneurial and epineurial lymphocytic infiltration. Immunomodulatory therapy alleviated the pain and fatigue and markedly improved distal motor latencies in both patients. Conclusions: DADS neuropathy can present with pain and a normal neurological examination apart from allodynia. Nerve conduction studies are necessary for diagnosis. These patients respond to immunotherapy better than typical DADS neuropathy patients with sensory ataxia. Muscle Nerve 54 : 973–977, 2016     

Inverted formin 2‐related Charcot‐Marie‐Tooth disease: extension of the mutational spectrum and pathological findings in Schwann cells and axons

Mutations in the gene encoding inverted formin FH2 and WH2 domain‐containing protein (INF2), a Cdc42 effector involved in the regulation of actin dynamics, cause focal segmental glomerulosclerosis (FSGS) and intermediate Charcot‐Marie‐Tooth neuropathy combined with FSGS (FSGS–CMT). Here, we report on six patients from four families with sensorimotor polyneuropathy and FSGS. Nerve conduction velocities were moderately slowed, and amplitudes of sensory and motor potentials were decreased. One patient had internal hydrocephalus and was intellectually disabled. Molecular genetic testing revealed two known and two novel missense mutations in the second and fourth exons of the INF2 gene. Investigations of one nerve biopsy confirmed the diagnosis of intermediate‐type CMT and revealed occasional abnormal in‐ and outfoldings of myelin sheaths and expansions of the endoplasmic reticulum in axons and Schwann cells. While earlier reports suggested that mutations causing FSGS‐CMT are restricted to exons 2 and 3 of the INF2 gene, we found one CMT‐FSGS causing mutation (p.Glu184Lys) in exon 4 extending the critical region of INF2 for rapid CMT‐FSGS molecular genetic diagnosis. Study of a nerve biopsy showed abnormalities that might be related to the known role of the INF2‐binding partner CDC42 in myelination.     

Delayed somatosensory conduction in acute painful neuropathy of diabetes

We examined the peripheral–central sensory conduction by using somatosensory evoked potential (SEP) in a 48 year old diabetic patient with acute painful neuropathy. The sural, ulnar and median sensory nerve conduction and SEP elicited by wrist stimulation showed no abnormalities, nevertheless, the tibial nerve SEP revealed absent spinal N19 and a remarkable delay of the cortical arrival time. These findings suggest involvement of the dorsal roots or the dorsal column in the acute painful neuropathy of diabetes.     

High glucose level as a modifier factor in CMT1A patients

Charcot‐Marie‐Tooth disease type 1A (CMT1A) is the most common type of hereditary neuropathy worldwide and diabetes mellitus (DM) is the most frequent cause of peripheral neuropathy in the Western world. CMT1A typically manifest as a predominant motor neuropathy, while, DM‐related neuropathy often manifests as a predominant sensory disorder. There are some evidences that CMT1A patients that also had DM had a more severe neuropathy. Although the real frequency and the underlying mechanisms related to this association has not yet been addressed in the literature. We sought to characterize the phenotypic variability of CMT1A patients with persistent high glucose levels (DM or impaired glucose tolerance [IGT]). Nineteen patients with CMT1A and DM (CMTdiab), seven with CMT1A and IGT (CMTintol) and 27 with CMT1A without comorbidities were analyzed. They were evaluated through clinical assessment, application of the following scales: visual analogue scale, McGill, CMTNS, SF‐36 and COMPASS 31 and electrophysiological studies. Patients CMTdiab had a more severe motor and sensory neuropathy, more intense autonomic symptoms and worse quality of life. Surprisingly, proximal weakness and temporal dispersion on nerve conduction studies are frequently observed in this group. Patients CMTintol also had a more severe neuropathy. Curiously, we observed that the association of CMT1A and glucose metabolism disorders (CMTglic) clustered in some families. Patients CMTglic develop a more severe neuropathy. As there is yet no cure to CMT1A, a strict blood sugar control may be a useful measure.     

Sensorimotor polyneuropathy in patients with SMA type‐1: Electroneuromyographic findings

Introduction: Generally, spinal muscular atrophy (SMA) is believed to be a pure motor neuron disease. We retrospectively evaluated our electrodiagnostic findings in SMA type 1 patients to demonstrate co‐existence of sensorimotor neuropathies. Methods: Electroneuromyographic (ENMG) studies in 15 patients (11 boys, 4 girls) were reviewed independently by 2 neurophysiologists. Upper extremity findings were compared with normal right arm controls. Results: Patient ages ranged from 1.5 to 26 months. Four SMA patients (26.7%) had decreased sensory nerve action potentials (SNAPs) or sensory nerve conduction velocities. Of them, median SNAPs could not be elicited in 3, and sural SNAPs could not be elicited in 2. Compound muscle action potential amplitudes were severely decreased in 14 (93.3%) and normal in 1. Conclusions: Survival motor neuron 1 (SMN1) gene analysis should be considered if clinical features are consistent with SMA, even if pathological or electrophysiological findings demonstrate peripheral sensorimotor polyneuropathies. Muscle Nerve, 2013