Spatial Fluctuation of Central Nervous System Lesions in X-linked Charcot-Marie-Tooth Disease with a Novel GJB1 Mutation

X-linked Charcot-Marie-Tooth disease type 1 (CMTX1), the most common form of CMTX, is caused by gap-junction beta 1 (GJB1) mutations. We herein report a 25-year-old Japanese man with disorientation, right hemiparesis, and dysarthria. Brain magnetic resonance imaging (MRI) showed high signal intensities in the bilateral cerebral white matter on diffusion-weighted imaging. He had experienced 2 episodes of transient central nervous system symptoms (at 7 and 13 years old). A genetic analysis identified a novel GJB1 mutation, c.169C>T, p.Gln57*. MRI abnormalities shifted from the cerebral white matter to the corpus callosum and had disappeared at the five-month follow-up. Transient changes between these lesions may indicate CMTX1.

A novel homozygous HPDL variant in Japanese siblings with autosomal recessive hereditary spastic paraplegia: case report and literature review

Biallelic variants of 4-hydroxyphenylpyruvate dioxygenase-like (HPDL) gene have been linked to neurodegenerative disorders ranging from severe neonatal encephalopathy to early-onset spastic paraplegia. We identified a novel homozygous variant, c.340G > T (p.Gly114Cys), in the HPDL gene in two siblings with autosomal recessive hereditary spastic paraplegia (HSP). Despite sharing the same likely pathogenic variant, the older sister had pure HSP, whereas her brother had severe and complicated HSP, accompanied by early-onset mental retardation and abnormalities in magnetic resonance imaging. Given the clinical heterogeneity and potential for treatable conditions in HPDL-related diseases, we emphasize the importance of genetic testing for the HPDL gene.

Dystonia and Parkinsonism in COA7-related disorders: expanding the phenotypic spectrum

BACKGROUND AND OBJECTIVE

Biallelic mutations in the COA7 gene have been associated with spinocerebellar ataxia with axonal neuropathy type 3 (SCAN3), and a notable clinical diversity has been observed. We aim to identify the genetic and phenotypic spectrum of COA7-related disorders.

METHODS

We conducted comprehensive genetic analyses on the COA7 gene within a large group of Japanese patients clinically diagnosed with inherited peripheral neuropathy or cerebellar ataxia.

RESULTS

In addition to our original report, which involved four patients until 2018, we identified biallelic variants of the COA7 gene in another three unrelated patients, and the variants were c.17A > G (p.D6G), c.115C > T (p.R39W), and c.449G > A (p.C150Y; novel). Patient 1 presented with an infantile-onset generalized dystonia without cerebellar ataxia. Despite experiencing an initial transient positive response to levodopa and deep brain stimulation, he became bedridden by the age of 19. Patient 2 presented with cerebellar ataxia, neuropathy, as well as parkinsonism, and showed a slight improvement upon levodopa administration. Dopamine transporter SPECT showed decreased uptake in the bilateral putamen in both patients. Patient 3 exhibited severe muscle weakness, respiratory failure, and feeding difficulties. A haplotype analysis of the mutation hotspot in Japan, c.17A > G (p.D6G), uncovered a common haplotype block.

CONCLUSION

COA7-related disorders typically encompass a spectrum of conditions characterized by a variety of major (cerebellar ataxia and axonal polyneuropathy) and minor (leukoencephalopathy, dystonia, and parkinsonism) symptoms, but may also display a dystonia-predominant phenotype. We propose that COA7 should be considered as a new causative gene for infancy-onset generalized dystonia, and COA7 gene screening is recommended for patients with unexplained dysfunctions of the central and peripheral nervous systems.

Clinical variability associated with intronic FGF14 GAA repeat expansion in Japan

BACKGROUND AND OBJECTIVES

The GAA repeat expansion within the fibroblast growth factor 14 (FGF14) gene has been found to be associated with late-onset cerebellar ataxia. This study aimed to investigate the genetic causes of cerebellar ataxia in patients in Japan.

METHODS

We collected a case series of 940 index patients who presented with chronic cerebellar ataxia and remained genetically undiagnosed after our preliminary genetic screening. To investigate the FGF14 repeat locus, we employed an integrated diagnostic strategy that involved fluorescence amplicon length analysis polymerase chain reaction (PCR), repeat-primed PCR, and long-read sequencing.

RESULTS

Pathogenic FGF14 GAA repeat expansions were detected in 12 patients from 11 unrelated families. The median size of the pathogenic GAA repeat was 309 repeats (range: 270-316 repeats). In these patients, the mean age of onset was 66.9 ± 9.6 years, with episodic symptoms observed in 56% of patients and parkinsonism in 30% of patients. We also detected FGF14 repeat expansions in a patient with a phenotype of multiple system atrophy, including cerebellar ataxia, parkinsonism, autonomic ataxia, and bilateral vocal cord paralysis. Brain magnetic resonance imaging (MRI) showed normal to mild cerebellar atrophy, and a follow-up study conducted after a mean period of 6 years did not reveal any significant progression.

DISCUSSION

This study highlights the importance of FGF14 GAA repeat analysis in patients with late-onset cerebellar ataxia, particularly when they exhibit episodic symptoms, or their brain MRI shows no apparent cerebellar atrophy. Our findings contribute to a better understanding of the clinical variability of GAA-FGF14-related diseases.

Genetic, electrophysiological, and pathological studies on patients with SCN9A-related pain disorders

BACKGROUND AND AIMS

Voltage-gated sodium channel Nav1.7, encoded by the SCN9A gene, has been linked to diverse painful peripheral neuropathies, represented by the inherited erythromelalgia (EM) and paroxysmal extreme pain disorder (PEPD). The aim of this study was to determine the genetic etiology of patients experiencing neuropathic pain, and shed light on the underlying pathogenesis.

METHODS

We enrolled eight patients presenting with early-onset painful peripheral neuropathies, consisting of six cases exhibiting EM/EM-like disorders and two cases clinically diagnosed with PEPD. We conducted a gene-panel sequencing targeting 18 genes associated with hereditary sensory and/or autonomic neuropathy. We introduced novel SCN9A mutation (F1624S) into a GFP-2A-Nav1.7rNS plasmid, and the constructs were then transiently transfected into HEK293 cells. We characterized both wild-type and F1624S Nav1.7 channels using an automated high-throughput patch-clamp system.

RESULTS

From two patients displaying EM-like/EM phenotypes, we identified two SCN9A mutations, I136V and P1308L. Among two patients diagnosed with PEPD, we found two additional mutations in SCN9A, F1624S (novel) and A1632E. Patch-clamp analysis of Nav1.7-F1624S revealed depolarizing shifts in both steady-state fast inactivation (17.4 mV, p < .001) and slow inactivation (5.5 mV, p < .001), but no effect on channel activation was observed.

INTERPRETATION

Clinical features observed in our patients broaden the phenotypic spectrum of SCN9A-related pain disorders, and the electrophysiological analysis enriches the understanding of genotype-phenotype association caused by Nav1.7 gain-of-function mutations.

Charcot-Marie-Tooth Disease with a Novel Variant in Gap Junction Protein Beta 1 Presenting with Visual Field Defects

Pathogenic variants in Gap Junction Protein Beta 1 (GJB1) cause X-linked Charcot-Marie-Tooth (CMT) disease type 1 (CMTX1), which is a common hereditary motor and sensory neuropathy. A 45-year-old man presented with progressive muscle weakness, atrophy, sensory disturbance of all limbs from childhood, and visual field defects in both eyes at 40 years old. A segregation analysis revealed a novel variant, c.173C>A (p.P58H), in the GJB1 gene. Patients with variants at codon 58 in GJB1 showed clinically varied phenotypes, ranging from demyelinating neuropathy to cerebellar ataxia. This patient may represent one of the various clinical phenotypes of GJB1 variants.

Clinical phenotypic diversity of NOTCH2NLC-related disease in the largest case series of inherited peripheral neuropathy in Japan

BACKGROUND

NOTCH2NLC GGC repeat expansions have been associated with various neurogenerative disorders, including neuronal intranuclear inclusion disease and inherited peripheral neuropathies (IPNs). However, only a few NOTCH2NLC-related disease studies in IPN have been reported, and the clinical and genetic spectra remain unclear. Thus, this study aimed to describe the clinical and genetic manifestations of NOTCH2NLC-related IPNs.

METHOD

Among 2692 Japanese patients clinically diagnosed with IPN/Charcot-Marie-Tooth disease (CMT), we analysed NOTCH2NLC repeat expansion in 1783 unrelated patients without a genetic diagnosis. Screening and repeat size determination of NOTCH2NLC repeat expansion were performed using repeat-primed PCR and fluorescence amplicon length analysis-PCR.

RESULTS

NOTCH2NLC repeat expansions were identified in 26 cases of IPN/CMT from 22 unrelated families. The mean median motor nerve conduction velocity was 41 m/s (range, 30.8-59.4), and 18 cases (69%) were classified as intermediate CMT. The mean age of onset was 32.7 (range, 7-61) years. In addition to motor sensory neuropathy symptoms, dysautonomia and involuntary movements were common (44% and 29%). Furthermore, the correlation between the age of onset or clinical symptoms and the repeat size remains unclear.

CONCLUSIONS

These findings of this study help us understand the clinical heterogeneity of NOTCH2NLC-related disease, such as non-length-dependent motor dominant phenotype and prominent autonomic involvement. This study also emphasise the importance of genetic screening, regardless of the age of onset and type of CMT, particularly in patients of Asian origin, presenting with intermediate conduction velocities and dysautonomia.

Case report: Mitochondrial trifunctional protein deficiency caused by HADHB gene mutation (c.1175C>T) characterized by higher brain dysfunction followed by neuropathy, presented gadolinium enhancement on brain imaging in an adult patient

Mitochondrial trifunctional protein (MTP) deficiency is an autosomal recessive disorder caused by impaired metabolism of long-chain fatty acids (LCFAs). Childhood and late-onset MTP deficiency is characterized by myopathy/rhabdomyolysis and peripheral neuropathy; however, the features are unclear. A 44-year-old woman was clinically diagnosed with Charcot-Marie-Tooth disease at 3 years of age due to gait disturbance. Her activity and voluntary speech gradually decreased in her 40s. Cognitive function was evaluated and brain imaging tests were performed. The Mini-Mental State Examination and frontal assessment battery scores were 25/30 and 10/18, respectively, suggesting higher brain dysfunction. Peripheral nerve conduction studies revealed axonal impairments. Brain computed tomography showed significant calcification. Magnetic resonance imaging revealed an increased gadolinium contrast-enhanced signal in the white matter, suggesting demyelination of the central nervous system (CNS) due to LCFAs. The diagnosis of MTP deficiency was confirmed through genetic examination. Administration of L-carnitine and a medium-chain fatty triglyceride diet was initiated, and the progression of higher brain dysfunction was retarded within 1 year. This patient's presentation was suggestive of CNS demyelination. The presence of brain calcification, higher brain dysfunction, or gadolinium enhancement in the white matter in patients with peripheral neuropathy may be suggestive of MTP deficiency.

HTLV-1-associated myelopathy/tropical spastic paraplegia with sporadic late-onset nemaline myopathy: a case report

BACKGROUND

Sporadic late onset nemaline myopathy (SLONM) is a muscle disorder characterized by the presence of nemaline rods in muscle fibers. SLONM has no known genetic cause but has been associated with monoclonal gammopathy of undetermined significance and with human immunodeficiency virus (HIV) infection. Human T-cell leukemia virus-1 (HTLV-1) is a known causative agent of adult T-cell leukemia/lymphoma and HTLV-1 associated myelopathy/tropical spastic paraplegia (HAM/TSP), a chronic inflammatory neurological disease. HTLV-1 has been reported to be implicated in inflammatory myopathies, as well as in HIV infection.; however, there have been no reports of an association between HTLV-1 infection and SLONM to date.

CASE PRESENTATION

A 70-year-old Japanese woman presented with gait disturbance, lumbar kyphosis, and respiratory dysfunction. The diagnosis of HAM/TSP with SLONM was made based on characteristic clinical symptoms of HAM/TSP, such as spasticity in the lower extremities, and cerebrospinal fluid test results; and of SLONM, such as generalized head drooping, respiratory failure, and muscle biopsy results. Steroid treatment was initiated and improvement in her stooped posture was observed after 3 days of treatment.

CONCLUSION

This is the first case report of SLONM combined with HTLV-1 infection. Further studies are needed to elucidate the relationship between retroviruses and muscle diseases.

Gene panel analysis of 119 index patients with suspected periodic paralysis in Japan

Introduction

Genetic factors are recognized as the major reason for patients with periodic paralysis. The goal of this study was to determine the genetic causes of periodic paralysis in Japan.

Methods

We obtained a Japanese nationwide case series of 119 index patients (108 men and 11 women) clinically suspected of periodic paralysis, and a gene panel analysis, targeting CACNA1S, SCN4A, and KCNJ2 genes, was conducted.

Results

From 34 cases, 25 pathogenic/likely pathogenic/unknown significance variants were detected in CACNA1S (nine cases), SCN4A (19 cases), or KCNJ2 (six cases), generating a molecular diagnostic rate of 28.6%. In total, seven variants have yet been found linked to periodic paralysis previously. The diagnostic yield of patients with hypokalemic and hyperkalemic periodic paralyzes was 26.2 (17/65) and 32.7% (17/52), respectively. A considerably higher yield was procured from patients with than without positive family history (18/25 vs. 16/94), onset age ≤20 years (24/57 vs. 9/59), or recurrent paralytic attacks (31/94 vs. 3/25).

Discussion

The low molecular diagnostic rate and specific genetic proportion of the present study highlight the etiological complexity of patients with periodic paralysis in Japan.

Efficacy of l-Arginine treatment in patients with HTLV-1-associated neurological disease

OBJECTIVE

HTLV-1 infection causes HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), resulting in loss of motor function. In this Phase 2 trial, we assessed the efficacy and safety of l-arginine in patients with HAM/TSP.

METHODS

This open-label, single-arm, Phase 2 study enrolled patients diagnosed with HAM/TSP. Patients received l-arginine at a dose of 20 g orally for 1 week and were followed-up for 3 weeks. The primary endpoint was change in walking speed in the 10-m walk test (10MWT). The main secondary endpoints were change in Timed Up and Go Test (TUGT) time, improvement in inflammatory markers in cerebrospinal fluid (CSF), safety, and tolerability.

RESULTS

The study enrolled 20 patients (13 [65%] female) with a mean age of 67.8 years (95% CI 62.3 to 73.3). Although the primary endpoint, the changes in 10MWT time between baseline (Day 0) and Day 7, did not reach statistical significance (mean percent change in time -3.5%, 95% CI -10.8% to 3.7%; P = 0.32), a significant improvement was detected between baseline and Day 14 (-9.4%, 95% CI -16.6% to -2.2%; P = 0.01). Significant improvements were also observed in selected secondary endpoints, including in TUGT time (-9.1%, 95% CI -15.5% to -2.7%; P < 0.01), and in neopterin concentration in CSF (-2.1 pmol/mL, 95% CI -3.8 to -0.5; P = 0.01). Adverse events were infrequent, mild, and resolved rapidly.

INTERPRETATION

l-arginine therapy improved motor function and decreased CSF inflammatory markers. l-arginine thus represents a promising therapeutic option for patients with HAM/TSP.

TRIAL REGISTRATION NUMBER

UMIN000023854.

Multi-type RFC1 repeat expansions as the most common cause of hereditary sensory and autonomic neuropathy

Non-coding repeat expansions within RFC1 and NOTCH2NLC genes have lately been linked to multisystem neurodegenerative diseases, which also shed light on yet undiagnosed patients with inherited peripheral neuropathies. The aim of this study was to identify the genetic basis of patients with hereditary sensory and autonomic neuropathy (HSAN). We collected 79 unrelated DNA samples clinically suspected with HSAN from multiple regions of Japan. Mutation screening was first performed using gene panel sequencing and whole-exome sequencing. Pathogenic/likely pathogenic variants were identified from genes of WNK1/HSN2 (6 cases), SCN9A (3 cases), NTRK1 (3 cases), and DNMT1 (2 cases). Subsequently, long-range flanking PCR and repeat-primed PCR were applied to analyze repeat expansions in RFC1 and NOTCH2NLC. Bi-allelic RFC1 repeat expansions were detected from 20 adult-onset HSAN patients, consisting of [(AAGGG)exp/(AAGGG)exp] (8 cases), [(ACAGG)exp/(ACAGG)exp] (8 cases), and [(AAGGG)exp/(ACAGG)exp] (4 cases). GGC repeat expansion in NOTCH2NLC was found in 1 case. Single-nucleotide variant-based haplotype analysis of patients harboring disease-associated repeat expansions in RFC1 revealed distinguishable haplotypes among subgroups with different repeat genotypes. These findings substantially redefine the genetic spectrum of HSAN, where multi-type RFC1 repeat expansions account for 25.3% of all patients, highlighting the necessity of genetic screening, particularly for adult-onset patients.

Genetic and clinical features of cerebellar ataxia with RFC1 biallelic repeat expansions in Japan

The recessive intronic pentanucleotide repeat AAGGG expansion of replication factor complex subunit 1 (RFC1) is associated with cerebellar ataxia, sensory neuropathy, and vestibular areflexia syndrome. And the clinical spectrum has been continuously expanding. We conducted this study to demonstrate the clinical and genetic features of a large-scale case series of Japanese patients with cerebellar ataxia with RFC1 repeat expansions. We examined 1,289 Japanese patients with cerebellar ataxia and analyzed RFC1 repeat expansions in 840 patients, excluding those with genetic diagnoses or an autosomal dominant inheritance pattern. For individuals where no product was obtained by flanking polymerase chain reaction (PCR), repeat-primed PCR was performed using primers specific for the following four repeat motifs: AAAAG, AAAGG, AAGGG, and ACAGG. RFC1 analysis revealed multitype biallelic pathogenic repeat expansions in 15 patients, including (AAGGG)exp/(AAGGG)exp in seven patients, (ACAGG)exp/(ACAGG)exp in three patients, (AAGGG)exp/(ACAGG)exp in four patients, and (AAGGG)exp/(AAAGG)₁₅(AAGGG)exp in one patient. Clinical analysis showed various combinations of cerebellar ataxia, vestibular dysfunction, neuropathy, cognitive decline, autonomic dysfunction, chronic cough, pyramidal tract disorder, parkinsonism, involuntary movement, and muscle fasciculation. Pathological RFC1 repeat expansions account for 1.8% (15/840) of undiagnosed patients with cerebellar ataxia and sporadic/recessive/unclassified inheritance. Screening of RFC1 repeat expansions should be considered in patients with cerebellar ataxia, irrespective of their subtype and onset age.

Comprehensive Genetic Analyses of Inherited Peripheral Neuropathies in Japan: Making Early Diagnosis Possible

Various genomic variants were linked to inherited peripheral neuropathies (IPNs), including large duplication/deletion and repeat expansion, making genetic diagnosis challenging. This large case series aimed to identify the genetic characteristics of Japanese patients with IPNs. We collected data on 2695 IPN cases throughout Japan, in which PMP22 copy number variation (CNV) was pre-excluded. Genetic analyses were performed using DNA microarrays, next-generation sequencing-based gene panel sequencing, whole-exome sequencing, CNV analysis, and RFC1 repeat expansion analysis. The overall diagnostic rate and the genetic spectrum of patients were summarized. We identified 909 cases with suspected IPNs, pathogenic or likely pathogenic variants. The most common causative genes were MFN2, GJB1, MPZ, and MME. MFN2 was the most common cause for early-onset patients, whereas GJB1 and MPZ were the leading causes of middle-onset and late-onset patients, respectively. Meanwhile, GJB1 and MFN2 were leading causes for demyelinating and axonal subtypes, respectively. Additionally, we identified CNVs in MPZ and GJB1 genes and RFC1 repeat expansions. Comprehensive genetic analyses explicitly demonstrated the genetic basis of our IPN case series. A further understanding of the clinical characteristics of IPN and genetic spectrum would assist in developing efficient genetic testing strategies and facilitate early diagnosis.

Novel heterozygous variants of SLC12A6 in Japanese families with Charcot-Marie-Tooth disease

BACKGROUND

Recessive mutations in SLC12A6 have been linked to hereditary motor sensory neuropathy with agenesis of the corpus callosum. Patients with early-onset peripheral neuropathy associated with SLC12A6 heterozygous variants were reported in 2016. Only five families and three variants have been reported to date, and the spectrum is unclear. Here, we aim to describe the clinical and mutation spectra of SLC12A6-related Charcot-Marie-Tooth (CMT) disease in Japanese patients.

METHODS

We extracted SLC12A6 variants from our DNA microarray and targeted resequencing data obtained from 2598 patients with clinically suspected CMT who were referred to our genetic laboratory by neurological or neuropediatric departments across Japan. And we summarized the clinical and genetic features of these patients.

RESULTS

In seven unrelated families, we identified one previously reported and three novel likely pathogenic SLC12A6 heterozygous variants, as well as two variants of uncertain significance. The mean age of onset for these patients was 17.5 ± 16.1 years. Regarding electrophysiology, the median motor nerve conduction velocity was 39.6 ± 9.5 m/sec. For the first time, we observed intellectual disability in three patients. One patient developed epilepsy, and her brain MRI revealed frontal and temporal lobe atrophy without changes in white matter and corpus callosum.

CONCLUSIONS

Screening for the SLC12A6 gene should be considered in patients with CMT, particularly those with central nervous system lesions, such as cognitive impairment and epilepsy, regardless of the CMT subtype.

A Novel PRPS1 Mutation in a Japanese Patient with CMTX5

The PRPS1 gene encodes phosphoribosyl pyrophosphate synthetase 1 (PRS-1). The phenotypes associated with PRPS1 mutations include DFN2 (mild PRS-1 deficiency), X-linked Charcot-Marie-Tooth disease type 5 (CMTX5) (moderate PRS-1 deficiency), Arts syndrome (severe PRS-1 deficiency), and PRS-1 superactivity1. CMTX5 is a very rare hereditary neuropathy characterized by deafness, optic atrophy, and polyneuropathy. We herein report a Japanese patient with CMTX5 who had a novel hemizygous mutation c.82 G>C in PRPS1. Despite showing a typical clinical picture, the decrease in enzyme activity measured in the patient's erythrocytes was milder than in previously reported cases.

An MFN2-related Charcot-Marie-Tooth Disease Patient with Optic Nerve Atrophy, Neurogenic Bladder Dysfunction, and Diaphragmatic Weakness

Charcot-Marie-Tooth disease (CMT) is a common hereditary peripheral polyneuropathy encompassing distinct monogenetic disorders. Pathogenic mutations in mitofusin 2 (MFN2) are the most frequent cause of its axonal type, CMT type 2A, with diverse phenotypes. We herein report a Japanese patient with a novel heterozygous MFN2 pathogenic variant (c.740 G>C, p.R247P) and severe CMT phenotypes, including progressive muscle weakness, optic atrophy, urinary inconsistency, and restrictive pulmonary dysfunction with eventration of the diaphragm that developed over her 60-year disease course. Our case expands the clinico-genetic features of MFN2-related CMT and highlights the need to evaluate infrequent manifestations during long-term care of CMT patients.

Novel de novo POLR3B mutations responsible for demyelinating Charcot-Marie-Tooth disease in Japan

Background

Biallelic POLR3B mutations cause a rare hypomyelinating leukodystrophy. De novo POLR3B heterozygous mutations were recently associated with afferent ataxia, spasticity, variable intellectual disability, and epilepsy, and predominantly demyelinating sensorimotor peripheral neuropathy.

Methods

We performed whole‐exome sequencing (WES) of DNA samples from 804 Charcot–Marie–Tooth (CMT) cases that could not be genetically diagnosed by DNA‐targeted resequencing microarray using next‐generation sequencers. Using WES data, we analyzed the POLR3B mutations and confirmed their clinical features.

Results

We identified de novo POLR3B heterozygous missense mutations in two patients. These patients presented with early‐onset demyelinating sensorimotor neuropathy without ataxia, spasticity, or cognitive impairment. Patient 1 showed mild cerebellar atrophy and spinal cord atrophy on magnetic resonance imaging and eventually died of respiratory failure in her 50s. We classified these mutations as pathogenic based on segregation studies, comparison with control database, and in silico analysis.

Conclusion

Our study is the third report on patients with demyelinating CMT harboring heterozygous POLR3B mutations and verifies the pathogenicity of POLR3B mutations in CMT. Although extremely rare in our large Japanese case series, POLR3B mutations should be added to the CMT‐related gene panel for comprehensive genetic screening, particularly for patients with early‐onset demyelinating CMT.

[A case of sporadic amyotrophic lateral sclerosis (ALS) with Senataxin (SETX) gene variant]

A 67-year-old man presented slowly progressive weakness of the extremities visited our hospital. Nerve conduction study showed axonal neuropathy and needle electromyography showed neurogenic changes with denervation findings in multiple limb muscles. While he was diagnosed as Probable amyotrophic lateral sclerosis (ALS), which is defined by the Awaji criteria for diagnosis of ALS, he did not develop either respiratory muscle paralysis or bulbar palsy, which are characteristic symptoms of sporadic ALS. Genetic testing revealed a novel gene variant in senataxin (SETX), the causative gene of ALS4. We could not make a definite diagnosis of ALS4 because he had no relatives who could perform genetic testing (segregation study). However, we considered the variant can be pathogenic because it was not previously reported and absent in at least 1,000 healthy control individuals, the variant site was highly conserved in mammals, and it may impair the function of senataxin protein (in silico analysis).

Sibling Cases of Charcot-Marie-Tooth Disease Type 4H with a Homozygous FGD4 Mutation and Cauda Equina Thickening

Charcot-Marie-Tooth disease type 4H (CMT4H) is an autosomal recessive inherited demyelinating neuropathy caused by an FYVE, RhoGEF, and a PH domain-containing protein 4 (FGD4) gene mutation. CMT4H is characterized by an early onset, slow progression, scoliosis, distal muscle atrophy, and foot deformities. We herein present sibling cases of CMT4H with a homozygous mutation in the FGD4 gene. Both patients exhibited cauda equina thickening on magnetic resonance imaging, which had not been reported among the previous CMT4H cases. This is the first report of CMT4H with a homozygous FGD4 c.1730G>A (p.Arg577Gln) mutation showing mild progression and cauda equina thickening.

Genetic spectrum of Charcot-Marie-Tooth disease associated with myelin protein zero gene variants in Japan

We aimed to reveal the genetic features associated with MPZ variants in Japan. From April 2007 to August 2017, 64 patients with 23 reported MPZ variants and 21 patients with 17 novel MPZ variants were investigated retrospectively. Variation in MPZ variants and the pathogenicity of novel variants was examined according to the American College of Medical Genetics standards and guidelines. Age of onset, cranial nerve involvement, serum creatine kinase (CK), and cerebrospinal fluid (CSF) protein were also analyzed. We identified 64 CMT patients with reported MPZ variants. The common variants observed in Japan were different from those observed in other countries. We identified 11 novel pathogenic variants from 13 patients. Six novel MPZ variants in eight patients were classified as likely benign or uncertain significance. Cranial nerve involvement was confirmed in 20 patients. Of 30 patients in whom serum CK levels were evaluated, eight had elevated levels. Most of the patients had age of onset >20 years. In another subset of 30 patients, 18 had elevated CSF protein levels; four of these patients had spinal diseases and two had enlarged nerve root or cauda equina. Our results suggest genetic diversity across patients with MPZ variants.

Cryptococcus Meningitis Can Co-occur with Anti-NMDA Receptor Encephalitis

We herein report a 50-year-old man with alcoholic cirrhosis who developed loss of consciousness and tremor of the upper limbs. Magnetic resonance imaging findings were suggestive of limbic encephalitis with bilateral hippocampal damage, and a cerebrospinal fluid (CSF) examination confirmed anti-N-methyl-D-aspartate (NMDA) and anti-glutamate receptor antibodies. Despite initial corticosteroid therapy, meningeal irritation symptoms appeared, owing to the development of cryptococcal meningitis (CM), diagnosed by the detection of cryptococcal capsular polysaccharide antigen in the follow-up CSF analysis. Cerebral infarction with reversible stenosis of major cerebral arteries during the clinical course was also observed. Following administration of antifungals and corticosteroids, the number of cells in the CSF gradually declined, and NMDA receptor antibodies disappeared. Our study demonstrates the unique coexistence of CM with anti-NMDA receptor encephalitis in adults.

[A case of motor and sensory polyneuropathy and respiratory failure with novel heterozygous mutation of the senataxin gene]

The patient was a 29-year-old male. He took his first steps at two-and-a-half years old, but his physical strength deteriorated and he became non-ambulatory at 12 years old. He had respiratory failure at the age of 20, and finally underwent tracheostomy with invasive positive-pressure ventilation (TPPV). He showed distal dominant muscle weakness and atrophy, including the face. Spinal scoliosis was recognized. He had peripheral predominance of sensory disorders. Nerve conduction studies showed a decrease of compound muscle action potential and a reduction of motor nerve conduction velocity. Sensory nerve action potential was not evoked. In genetic analysis, c.23 C> T (p. T8M) heterozygous mutation was found in the senataxin gene (SETX). Although SETX is a causative gene of familial amyotrophic lateral sclerosis type 4 (ALS4), this case suggests that SETX mutation can also cause motor and sensory polyneuropathy.

(Pro)renin receptor accelerates development of sarcopenia via activation of Wnt/YAP signaling axis

To extend life expectancy and ensure healthy aging, it is crucial to prevent and minimize age‐induced skeletal muscle atrophy, also known as sarcopenia. However, the disease's molecular mechanism remains unclear. The age‐related Wnt/β‐catenin signaling pathway has been recently shown to be activated by the (pro)renin receptor ((P)RR). We report here that (P)RR expression was increased in the atrophied skeletal muscles of aged mice and humans. Therefore, we developed a gain‐of‐function model of age‐related sarcopenia via transgenic expression of (P)RR under control of the CAG promoter. Consistent with our hypothesis, (P)RR‐Tg mice died early and exhibited muscle atrophy with histological features of sarcopenia. Moreover, Wnt/β‐catenin signaling was activated and the regenerative capacity of muscle progenitor cells after cardiotoxin injury was impaired due to cell fusion failure in (P)RR‐Tg mice. In vitro forced expression of (P)RR protein in C2C12 myoblast cells suppressed myotube formation by activating Wnt/β‐catenin signaling. Administration of Dickkopf‐related protein 1, an inhibitor of Wnt/β‐catenin signaling, and anti‐(P)RR neutralizing antibody, which inhibits binding of (P)RR to the Wnt receptor, significantly improved sarcopenia in (P)RR‐Tg mice. Furthermore, the use of anti‐(P)RR neutralizing antibodies significantly improved the regenerative ability of skeletal muscle in aged mice. Finally, we show that Yes‐associated protein (YAP) signaling, which is coordinately regulated by Wnt/β‐catenin, contributed to the development of (P)RR‐induced sarcopenia. The present study demonstrates the use of (P)RR‐Tg mice as a novel sarcopenia model, and shows that (P)RR‐Wnt‐YAP signaling plays a pivotal role in the pathogenesis of this disease.

Long-read sequencing identifies GGC repeat expansions in NOTCH2NLC associated with neuronal intranuclear inclusion disease

. The average onset age is 59.7 years among approximately 140 NIID cases consisting of mostly sporadic and several familial cases. By linkage mapping of a large NIID family with several affected members (Family 1), we identified a 58.1 Mb linked region at 1p22.1-q21.3 with a maximum logarithm of the odds score of 4.21. By long-read sequencing, we identified a GGC repeat expansion in the 5' region of NOTCH2NLC (Notch 2 N-terminal like C) in all affected family members. Furthermore, we found similar expansions in 8 unrelated families with NIID and 40 sporadic NIID cases. We observed abnormal anti-sense transcripts in fibroblasts specifically from patients but not unaffected individuals. This work shows that repeat expansion in human-specific NOTCH2NLC, a gene that evolved by segmental duplication, causes a human disease.

Mutations in COA7 cause spinocerebellar ataxia with axonal neuropathy

Several genes related to mitochondrial functions have been identified as causative genes of neuropathy or ataxia. Cytochrome c oxidase assembly factor 7 (COA7) may have a role in assembling mitochondrial respiratory chain complexes that function in oxidative phosphorylation. Here we identified four unrelated patients with recessive mutations in COA7 among a Japanese case series of 1396 patients with Charcot-Marie-Tooth disease (CMT) or other inherited peripheral neuropathies, including complex forms of CMT. We also found that all four patients had characteristic neurological features of peripheral neuropathy and ataxia with cerebellar atrophy, and some patients showed leukoencephalopathy or spinal cord atrophy on MRI scans. Validated mutations were located at highly conserved residues among different species and segregated with the disease in each family. Nerve conduction studies showed axonal sensorimotor neuropathy. Sural nerve biopsies showed chronic axonal degeneration with a marked loss of large and medium myelinated fibres. An immunohistochemical assay with an anti-COA7 antibody in the sural nerve from the control patient showed the positive expression of COA7 in the cytoplasm of Schwann cells. We also observed mildly elevated serum creatine kinase levels in all patients and the presence of a few ragged-red fibres and some cytochrome c oxidase-negative fibres in a muscle biopsy obtained from one patient, which was suggestive of subclinical mitochondrial myopathy. Mitochondrial respiratory chain enzyme assay in skin fibroblasts from the three patients showed a definitive decrease in complex I or complex IV. Immunocytochemical analysis of subcellular localization in HeLa cells indicated that mutant COA7 proteins as well as wild-type COA7 were localized in mitochondria, which suggests that mutant COA7 does not affect the mitochondrial recruitment and may affect the stability or localization of COA7 interaction partners in the mitochondria. In addition, Drosophila COA7 (dCOA7) knockdown models showed rough eye phenotype, reduced lifespan, impaired locomotive ability and shortened synaptic branches of motor neurons. Our results suggest that loss-of-function COA7 mutation is responsible for the phenotype of the presented patients, and this new entity of disease would be referred to as spinocerebellar ataxia with axonal neuropathy type 3.

Genetic profile and onset features of 1005 patients with Charcot-Marie-Tooth disease in Japan

OBJECTIVE : To identify the genetic characteristics in a large-scale of patients with Charcot-Marie-Tooth disease (CMT). METHODS: From May 2012 to August 2016, we collected 1005 cases with suspected CMT throughout Japan, whereas PMP22 duplication/deletion were excluded in advance for demyelinating CMT cases. We performed next-generation sequencing targeting CMT-related gene panels using Illumina MiSeq or Ion Proton, then analysed the gene-specific onset age of the identified cases and geographical differences in terms of their genetic spectrum. RESULTS : From 40 genes, we identified pathogenic or likely pathogenic variants in 301 cases (30.0%). The most common causative genes were GJB1 (n=66, 21.9%), MFN2 (n=66, 21.9%) and MPZ (n=51, 16.9%). In demyelinating CMT, variants were detected in 45.7% cases, and the most common reasons were GJB1 (40.3%), MPZ (27.1%), PMP22 point mutations (6.2%) and NEFL (4.7%). Axonal CMT yielded a relatively lower detection rate (22.9%), and the leading causes, occupying 72.4%, were MFN2 (37.2%), MPZ (9.0%), HSPB1 (8.3%), GJB1 (7.7%), GDAP1 (5.1%) and MME (5.1%). First decade of life was found as the most common disease onset period, and early-onset CMT cases were most likely to receive a molecular diagnosis. Geographical distribution analysis indicated distinctive genetic spectrums in different regions of Japan. CONCLUSIONS : Our results updated the genetic profile within a large-scale of Japanese CMT cases. Subsequent analyses regarding onset age and geographical distribution advanced our understanding of CMT, which would be beneficial for clinicians.

X-linked Charcot-Marie-Tooth disease type 5 with recurrent weakness after febrile illness

X-linked Charcot-Marie-Tooth disease type 5 (CMTX5) is an X-linked disorder characterized by early-onset sensorineural hearing impairment, peripheral neuropathy, and progressive optic atrophy. It is caused by a loss-of-function mutation in the phosphoribosyl pyrophosphate synthetase 1 gene (PRPS1), which encodes isoform I of phosphoribosyl pyrophosphate synthetase (PRS-I). A decreased activity leads to nonsyndromic sensorineural deafness (DFN2), CMTX5, and Arts syndrome depending upon residual PRS-I activity. Clinical and neurophysiological features of pediatric CMTX5 are poorly defined. We report two male siblings with peripheral neuropathy and prelingual sensorineural hearing loss who carried a novel c.319A>G (p.Ile107Val) PRPS1 missense mutation. They exhibited recurrent episodes of transient proximal muscle weakness, showing Gowers' sign and waddling gait after suffering from febrile illness. This transient weakness has not been previously reported in CMTX5. A patient with Arts syndrome was reported to have transient proximal weakness after febrile illness. The transient weakness presenting in both CMTX5 and Arts syndrome suggests an overlap of signs and a continuous spectrum of PRS-I hypoactivity disease. Children presenting with transient neurological signs should be evaluated for peripheral neuropathy and consider genetic analysis for PRPS1.

Peripheral neuropathy in a case with CADASIL: a case report

Background

Case presentation

Conclusions

Electronic supplementary material

Genetic and phenotypic profile of 112 patients with X-linked Charcot-Marie-Tooth disease type 1

BACKGROUND AND PURPOSE

X-linked Charcot-Marie-Tooth disease type 1 (CMTX1), caused by mutations in gap junction protein beta 1 (GJB1), is characterized by various central nervous system symptoms and gender differences of clinical severity. The aim of this study was to identify the frequency and mutation spectrum of CMTX1 patients in Japan and to demonstrate their phenotypic diversities.

METHODS

Using three high-throughput sequencing systems, targeted gene panel sequencing on 1483 unrelated index patients with suspected Charcot-Marie-Tooth (CMT) disease was performed. The peripheral and central nervous system involvements of all patients with GJB1 variants were assessed retrospectively and a detailed gender comparison was conducted with the CMT examination score.

RESULTS

Twenty-three novel and 36 described GJB1 variants were identified from 88 pedigrees, in which 34 female and 78 male patients were enrolled. Mean age at onset of the male patients was much younger than the females, 21.56 ± 17.63 years vs. 35.53 ± 23.72 years (P = 0.007). Male patients presented with more severe phenotypes in every examination item, but statistical differences were observed only in motor dysfunctions of the lower extremities and vibration sensation. No significant sensory difference was identified between genders, either clinically or electrophysiologically. Central nervous system dysfunctions were found in 15 patients from 12 pedigrees. Therein, six patients developed stroke-like phenotypes, with dysarthria as the leading symptom.

CONCLUSIONS

A relatively lower frequency of CMTX1 (5.9%) was demonstrated and a broad mutation spectrum of GJB1 was described. Detailed clinical differences between genders and various central nervous system symptoms were also illustrated, even in the same pedigree.

[Charcot-Marie-Tooth disease showing transient central nervous system lesions after a large amount of alcohol intake: A case report]

A 23-year-old man experienced numbness in the perioral region and right arm, and right leg weakness on the second day after drinking a large amount of alcohol during foreign travel. His symptoms disappeared but then reappeared repetitively. Cerebral MRI performed on the third day after onset showed multiple white matter lesions; however, these lesions disappeared 26 days after onset. Neurological examination and nerve conduction studies revealed demyelinating polyneuropathy. Genetic testing for Charcot-Marie-Tooth disease, X-linked dominant 1 (CMTX1) due to GJB1 mutation was conducted based on the symptoms of transient central nervous system lesions and polyneuropathy exhibited by the patient and his mother. As a result, a c.530T>C (p.V177A) substitution in exon 2 of GJB1 was identified. CMTX1 patients should be advised to avoid excessive drinking because this could induce central nervous system lesions.

[Transient, recurrent, white matter lesions in X-linked Charcot-Marie-Tooth disease with heterozygote mutation of GJB1 gene: case report of a female patient]

A 32-year-old woman showed transient central type facial nerve palsy and bulbar symptoms. Brain MRI revealed high intensity signals in the cerebral white matter, splenium of corpus callosum, and posterior limb of internal capsule. Two elder brothers of the patient had distal dominant peripheral neuropathies in four limbs. In this family, the point mutation of GJB1 gene, encoding connexin 32, was revealed and X-linked Charcot-Marie-Tooth disease (CMTX1) was diagnosed. The presented case was a heterozygote of this mutation. She showed severe transient central nervous system (CNS) symptoms and subclinical demyelinating peripheral neuropathy. The CNS symptoms and alterations of brain images were very similar among three siblings. There are many reports on male patients with CMTX1 who show associated CN symptoms, but female patients are very rare. There has been no previous report of a CMTX1 patient similar to the patient presented here. The trigger factors have been recognized at the onset of transient CN symptoms in these cases. The prevention of these factors is important for the management of such patients.

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.

Peripheral nerve pathology at fixed stage in spinal muscular atrophy with respiratory distress type 1

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is characterized by severe respiratory failure due to diaphragmatic paralysis and distal muscular weakness in early infancy. After an initial decline in respiratory state and motor function until 1-2years of age, residual capabilities reach a plateau. We report the peripheral neuropathological findings of a patient with SMARD1 at 1year and 1month of age, when his muscle strength and respiratory symptoms had deteriorated and then stabilized for several months. Peripheral nerve biopsy revealed severely progressed axonal degeneration. This finding suggests the rapid progression of peripheral axonal neuropathy in SMARD1 that leads to its characteristic clinical course of respiratory failure and paralysis in the early infantile period.

[A case of chronic progressive neuro-Behçet disease with extensive cerebral atrophy and elevated CSF IL-6 activity treated with infliximab]

A 43-year-old man without a previous episode of uveitis presented with slowly progressive neurological symptoms that appeared within the past year such as dysarthria, ataxic gait, and behavioral changes. Brain MRI findings showed atrophic lesions in the brainstem and cerebellum. Because these clinical symptoms and abnormal MRI findings indicated spinocerebellar degeneration as the initial diagnosis, he was admitted to our hospital. On admission, we noticed that he had non-neurological manifestations of Behçet disease, such as stomatitis, genital ulcers, and folliculitis. HLA-B51 was positive. He also showed pleocytosis (29 cells/mm³, predominantly mononuclear cells) and elevated cerebrospinal fluid (CSF) IL-6 levels (213 pg/ml), hence he was diagnosed with chronic progressive neuro-Behçet disease (CPNBD). The therapeutic effect of a high-dose intravenous methylprednisolone pulse (1,000 mg/day for 3 days) and methotrexate (maximum dosage, 16 mg/week) was poor against both neurological symptoms and CSF findings. Intravenous infliximab therapy (5 mg/kg, 2 weeks) dramatically decreased CSF IL-6 levels (13 pg/ml) but clinical symptoms remained unchanged. MRI findings of extensive cerebral atrophy and increased CSF IL-6 levels at the pretreatment time point reflected irreversible neurological involvement in CPNBD. For cases with progressive psychiatric symptoms and cerebellar ataxia in the early stage of the disease, skin manifestations should be examined immediately, CSF IL-6 levels measured, and immunosuppressive therapy initiated before CPNBD progresses to brainstem atrophy.

Histopathological features of a patient with Charcot-Marie-Tooth disease type 2U/AD-CMTax-MARS

Charcot-Marie-Tooth (CMT) disease is a complex of peripheral nervous system disorders. CMT type 2U (CMT2U) is an autosomal dominant (AD) disease caused by mutations in the MARS gene encoding methionyl-tRNA synthetase; this disease has thus been newly called AD-CMTax-MARS. A few families with mutations in the MARS gene have been reported, without detailed histopathological findings. We describe a 70-year-old woman who had bilateral dysesthesia of the soles since the age of 66 years. Sural nerve biopsy showed a decrease in the density of large myelinated nerve fibers. Increased clusters of regenerating myelinated nerve fibers were noted. Electron microscopic analyses revealed degeneration of unmyelinated nerves. There was no vasculitis or inflammatory cell infiltration. Genetic analysis identified a heterozygous p.P800T mutation, a reported mutation in the MARS gene. We report the detailed histopathological findings in a patient with CMT2U/AD-CMTax-MARS. The findings are similar to those found in CMT2D caused by mutations in the GARS gene, encoding glycyl-tRNA synthetase.

Clinical and mutational spectrum of Japanese patients with recessive variants in SH3TC2

SH3TC2, known as the causative gene of autosomal recessive demyelinating Charcot-Marie-Tooth type 4C (CMT4C), was also found linked to a mild mononeuropathy of the median nerve with an autosomal dominant inheritance pattern. Using DNA microarray, Illumina MiSeq, and Ion proton, we carried out gene panel sequencing among 1483 Japanese CMT patients, containing 397 patients with demyelinating CMT. From seven patients with demyelinating CMT, we identified eight recessive variants in the SH3TC2 gene, consisting of five novel (pathogenic/likely pathogenic) and three reported variants. Additionally, from two patients with axonal CMT, we detected a reported recessive variant, p.Arg77Trp, which was herein reclassified as variant with unknown significance. Of the seven CMT4C patients (six females and one male), 2/7 patients developed symptoms at their first decade, and 5/7 patients lost their ambulation around age 50. Scoliosis was observed from more than half (4/7) of these patients, whereas hearing loss is the most common symptom of central nervous system (6/7). No median nerve mononeuropathy was recorded from their family members. We identified recessive variants in SH3TC2 from 1.76% of demyelinating CMT patients. An uncommon gender difference was recognized and the wild spectrum of these variants suggests mutational diversity of SH3TC2 in Japan.

[A amyotrophic lateral sclerosis (ALS) 4 family misdiagnosed as hereditary spastic paraplegia-a case report]

We report a 44 years old man with slowly progressive muscular atrophy of the extremities for over 30 years. He experienced difficulty in walking in his 10's and was diagnosed as hereditary spastic paraplegia (HSP) in his 20's. And then, muscle atrophy of the extremities slowly progressed especially in his distal muscles. Sensory axonal neuropathy was detected with sural nerve biopsy. His father and uncle have been diagnosed as HSP in their early days. His father noticed weakness of his leg in his 20's. He lost motor function of the leg in his 60's. In addition, marked disturbance of thermal sensation, vibration, and sense of position were found by physical examination. Our genetic study detected senataxin (SETX) gene mutation (c.8C>T,p.T3I) in the blood of those two patients, and they had been identified as family cases of amyotrophic lateral sclerosis (ALS) 4. As clinical symptoms of ALS4 would be similar to those of HSP at the onset, we suggest considering ALS4 in seeing patients with HSP without gene diagnosis.

A novel mutation in FGD4 causes Charcot-Marie-Tooth disease type 4H with cranial nerve involvement

Charcot-Marie-Tooth disease type 4H (CMT4H) is a rare variant of autosomal recessive hereditary neuropathy. It is caused by FGD4 mutations and characterized by early infantile onset, slowly progressive distal muscle weakness, scoliosis, and myelin outfoldings visible in nerve biopsy samples. Here, we report a 65-year-old male born to consanguineous parents, who carries a novel homozygous FGD4 c.724C>T nonsense mutation. He developed lower limb weakness in his teens, which progressed slowly and was accompanied by diplopia, bilateral hearing loss, and erectile dysfunction from his twenties. At the age of 65, he was wheelchair-bound and had mild scoliosis, bilateral ophthalmoplegia, facial muscle weakness, inner ear hearing loss, distal-dominant weakness, and sensory disturbance, but no cognitive deterioration. Magnetic resonance imaging revealed enlarged bilateral trigeminal and facial nerves. Accordingly, we believe that this mutation causes slowly progressive sensorimotor neuropathy with apparent cranial nerve involvement, thereby further expanding the clinical spectrum of CMT4H.

Clinical and mutational spectrum of Charcot-Marie-Tooth disease type 2Z caused by MORC2 variants in Japan

BACKGROUND AND PURPOSE

The microrchidia family CW-type zinc finger 2 gene (MORC2) was newly identified as a causative gene of Charcot-Marie-Tooth disease (CMT) type 2Z in 2016. We aimed to describe the clinical and mutational spectrum of patients with CMT harboring MORC2 mutations in Japan.

METHODS

We analyzed samples from 781 unrelated patients clinically diagnosed with CMT using deoxyribonucleic acid microarray or targeted resequencing by next-generation sequencing, and samples from 434 mutation-negative patients were subjected to whole-exome sequencing. We extracted MORC2 variants from these whole-exome sequencing data and classified them according to American College of Medical Genetics standards and guidelines.

RESULTS

We identified MORC2 variants in 13 patients. As the second most common causative gene of CMT type 2 after MFN2, MORC2 variants were detected in 2.7% of patients with CMT type 2. The mean age of onset was 10.3 ± 8.7 years, and the inheritance pattern was mostly sporadic (11/13 patients, 84.6%). The clinical phenotype was typically length-dependent polyneuropathy, and electrophysiological studies revealed sensory-dominant axonal neuropathy. Mental retardation was identified in 4/13 patients (30.8%). p.Arg190Trp, as a mutational hotspot, was observed in eight unrelated families. We also identified two novel probably pathogenic variants, p.Cys345Tyr and p.Ala369Val, and one novel uncertain significance variant, p.Tyr332Cys.

CONCLUSIONS

Our study is the largest report of patients harboring MORC2 variants. We revealed a clinical and mutational spectrum of Japanese patients with MORC2 variants. More attention should be paid to cognitive impairment, and the responsible mechanism requires further research for elucidation.

Clinical and genetic diversities of Charcot-Marie-Tooth disease with MFN2 mutations in a large case study

Charcot-Marie-Tooth disease (CMT) constitutes a heterogeneous group affecting motor and sensory neurons in the peripheral nervous system. MFN2 mutations are the most common cause of axonal CMT. We describe the clinical and mutational spectra of CMT patients harboring MFN2 mutations in Japan. We analyzed 1,334 unrelated patients with clinically suspected CMT referred by neurological and neuropediatric departments throughout Japan. We conducted mutation screening using a DNA microarray, targeted resequencing, and whole-exome sequencing. We identified pathogenic or likely pathogenic MFN2 variants from 79 CMT patients, comprising 44 heterozygous and 1 compound heterozygous variants. A total of 15 novel variants were detected. An autosomal dominant family history was determined in 43 cases, and the remaining 36 cases were reported as sporadic with no family history. The mean onset age of CMT in these patients was 12 ± 14 (range 0-59) years. We observed neuropathic symptoms in all patients. Some had optic atrophy, vocal cord paralysis, or spasticity. We detected a compound heterozygous MFN2 mutation in a patient with a severe phenotype and the co-occurrence of MFN2 and PMP22 mutations in a patient with an uncommon phenotype. MFN2 is the most frequent causative gene of CMT2 in Japan. We present 15 novel variants and broad clinical and mutational spectra of Japanese MFN2-related CMT patients. Regardless of the onset age and inheritance pattern, MFN2 gene analysis should be performed. Combinations of causative genes should be considered to explain the phenotypic diversity.

Clinical and mutational spectrum of Japanese patients with Charcot-Marie-Tooth disease caused by GDAP1 variants

BACKGROUND

Mutations in GDAP1 are responsible for heterogeneous clinical and electrophysiological phenotypes of Charcot-Marie-Tooth disease (CMT), with autosomal dominant or recessive inheritance pattern. The aim of this study is to identify the clinical and mutational spectrum of CMT patients with GDAP1 variants in Japan.

MATERIALS AND METHODS

From April 2007 to October 2014, using three state-of-art technologies, we conducted gene panel sequencing in a cohort of 1,030 patients with inherited peripheral neuropathies (IPNs), and 398 mutation-negative cases were further analyzed with whole-exome sequencing.

RESULTS

We identified GDAP1 variants from 10 patients clinically diagnosed with CMT. The most frequent recessive variant in our cohort (5/10), c.740C>T (p.A247V), was verified to be associated with a founder event. We also detected three novel likely pathogenic variants: c.928C>T (p.R310W) and c.546delA (p.E183Kfs*23) in Case 2 and c.376G>A (p.E126K) in Case 8. Nerve conduction study or sural nerve biopsy of all 10 patients indicated axonal type peripheral neuropathy.

CONCLUSION

We identified GDAP1 variants in approximately 1% of our cohort with IPNs, and established a founder mutation in half of these patients. Our study originally described the mutational spectrum and clinical features of GDAP1-related CMT patients in Japan.

Clinical diversity caused by novel IGHMBP2 variants

Immunoglobulin helicase μ-binding protein 2 (IGHMBP2) gene is responsible for Charcot-Marie-Tooth disease (CMT) type 2S and spinal muscular atrophy with respiratory distress type 1 (SMARD1). From June 2014 to December 2015, we collected 408 cases, who referred to our genetic laboratory for genetic analysis, suspected with CMT disease or other inherited peripheral neuropathies (IPNs) on the basis of clinical manifestations and electrophysiological studies. Mutation screening was performed using Ion AmpliSeq Custom Panels, which comprise 72 disease-causing or candidate genes of IPNs. We identified novel homozygous or compound heterozygous variants of IGHMBP2 in four patients. Three patients presented with childhood-onset axonal predominant sensorimotor polyneuropathies, whereas the other case was diagnosed with SMARD1, manifesting as low birth weight, weak cry, reduced spontaneous movement and developed respiratory distress 4 months after birth. We present the original report of CMT type 2S in Japan, and illustrate that recessive IGHMBP2 variants account for ~1.6% of axonal CMT in our cohort.