Yujiro Higuchi

Mutations in MME cause an autosomal-recessive Charcot–Marie–Tooth disease type 2

The objective of this study was to identify new causes of Charcot–Marie–Tooth (CMT) disease in patients with autosomal‐recessive (AR) CMT.

Nerve ultrasound depicts peripheral nerve enlargement in patients with genetically distinct Charcot-Marie-Tooth disease

Objective To elucidate the ultrasound (US) features of peripheral nerves including nerve roots in patients with different types of Charcot-Marie-Tooth disease (CMT), and the association between US findings, clinical features and parameters of nerve conduction studies (NCS) in CMT1A. Methods US of median, sural and great auricular nerves and the C6 nerve root was performed in patients with CMT1A (n=20), MPZ-associated CMT (n=3), NEFL-associated CMT (n=4), EGR2-associated CMT (n=1), ARHGEF10-associated CMT (n=1) and in controls (n=30). In patients with CMT1A, we analysed the correlations between US findings and the following parameters: age, CMT Neuropathy Score (CMTNS) and NCS indices of the median nerve. Results Cross-sectional areas (CSAs) of all the nerves were significantly increased in patients with CMT1A compared with that in controls. In MPZ-associated CMT, increased CSAs were found in the median nerve at wrist and in the great auricular nerve, whereas it was not increased in patients with NEFL-associated CMT. In patients with CMT1A, there was a positive correlation between CMTNS and the CSAs in the median nerves or great auricular nerves. In median nerves in patients with CMT1A, we found a negative correlation between the nerve conduction velocity and the CSA. Conclusions Nerve US may aid in differentiating among the subtypes of CMT in combination with NCS. In CMT1A, the median nerve CSA correlates with the disease severity and peripheral nerve function.

Hereditary sensory and autonomic neuropathy type IID caused by an SCN9A mutation

Objective: To identify the clinical features of Japanese patients with suspected hereditary sensory and autonomic neuropathy (HSAN) on the basis of genetic diagnoses. Methods: On the basis of clinical, in vivo electrophysiologic, and pathologic findings, 9 Japanese patients with sensory and autonomic nervous dysfunctions were selected. Eleven known HSAN disease–causing genes and 5 related genes were screened using a next-generation sequencer. Results: A homozygous mutation, c.3993delGinsTT, was identified in exon 22 of SCN9A from 2 patients/families. The clinical phenotype was characterized by adolescent or congenital onset with loss of pain and temperature sensation, autonomic nervous dysfunctions, hearing loss, and hyposmia. Subsequently, this mutation was discovered in one of patient 1s sisters, who also exhibited sensory and autonomic nervous system dysfunctions, with recurrent fractures being the most predominant feature. Nerve conduction studies revealed definite asymmetric sensory nerve involvement in patient 1. In addition, sural nerve pathologic findings showed loss of large myelinated fibers in patient 1, whereas the younger patient showed normal sural nerve pathology. Conclusions: We identified a novel homozygous mutation in SCN9A from 2 Japanese families with autosomal recessive HSAN. This loss-of-function SCN9A mutation results in disturbances in the sensory, olfactory, and autonomic nervous systems. We propose that SCN9A mutation results in the new entity of HSAN type IID, with additional symptoms including hyposmia, hearing loss, bone dysplasia, and hypogeusia.

Novel mutation in the replication focus targeting sequence domain of DNMT1 causes hereditary sensory and autonomic neuropathy IE

DNMT1, encoding DNA methyltransferase 1 (Dnmt1), is a critical enzyme which is mainly responsible for conversion of unmethylated DNA into hemimethylated DNA. To date, two phenotypes produced by DNMT1 mutations have been reported, including hereditary sensory and autonomic neuropathy (HSAN) type IE with mutations in exon 20, and autosomal dominant cerebellar ataxia, deafness, and narcolepsy caused by mutations in exon 21. We report a sporadic case in a Japanese patient with loss of pain and vibration sense, chronic osteomyelitis, autonomic system dysfunctions, hearing loss, and mild dementia, but without definite cerebellar ataxia. Electrophysiological studies revealed absent sensory nerve action potential with nearly normal motor nerve conduction studies. Brain magnetic resonance imaging revealed mild diffuse cerebral and cerebellar atrophy. Using a next‐generation sequencing system, 16 candidate genes were analyzed and a novel missense mutation, c.1706A>G (p.His569Arg), was identified in exon 21 of DNMT1. Our findings suggest that mutation in exon 21 of DNMT1 may also produce a HSAN phenotype. Because all reported mutations of DNMT1 are concentrated in exons 20 and 21, which encode the replication focus targeting sequence (RFTS) domain of Dnmt1, the RFTS domain could be a mutation hot spot.

Clinicopathological features of the first Asian family having vocal cord and pharyngeal weakness with distal myopathy due to a MATR3 mutation

Distal myopathy is a clinically and pathologically heterogeneous disorder that selectively or disproportionately affects distal muscles of the upper and/or lower limbs [1]. An adult-onset, progressive autosomal dominant distal myopathy that is frequently associated with dysphagia and dysphonia, vocal cord and pharyngeal weakness (VCPDM/MPD2) was recently discovered in a North American and a Bulgarian family; its causative agent being a missense mutation in the matrin-3 (MATR3) gene [2,3]. Still, VCPDM remains a fairly rare disease that has only been reported in two families worldwide so far. According to a previous report on VCPDM, muscle biopsy performed on the quadriceps or gastrocnemius muscles revealed chronic non-inflammatory myopathy with subsarcolemmal rimmed vacuoles (RV) and atrophic fibres, with denervation [2]. Pathologic changes were reported to be more severe in the gastrocnemius than in the quadriceps muscles. Electrophysiological studies have also shown some degree of combination of myogenic and neurogenic changes associated with VCPDM [2]. Here, we report the clinicopathological features of the first Asian family having VCPDM with a missense mutation in the MATR3 gene. We also examined whether muscle pathology in patients with VCPDM shared histopathological characteristics with other myopathies with RV, including sporadic inclusion body myositis (sIBM), oculopharyngeal muscular dystrophy (OPMD), glucosamine (UDP-N-acetyl)-2-epimerase/Nacetylmannosamine kinase (GNE) myopathy, and valosin-containing protein (VCP) myopathy. Two Japanese half sisters were examined and summarized in Table 1. Their father noticed a disturbance in his gait in his forties and was dependent on a powered wheelchair in his sixties. He gradually developed respiratory problems and eventually underwent a tracheostomy with mechanical ventilation. He died of respiratory failure at 73. Case 1, a 44-year-old woman experienced difficulty in ambulation and developed dysphagia of liquid and solids. Upon admission to our hospital, her neurological examination revealed dysphagia and dysarthria, while facial weakness and tongue atrophy were not observed. Moderate muscle weakness was detected in the neck flexor, and mild weakness without fasciculation was observed in the iliopsoas, hamstring, and tibialis anterior muscles. Touch and pinprick sensations were reduced in the distal upper and lower limbs, while vibration and position sense remained intact. Tendon reflexes, especially in the patella tendons, were generally weak. Case 2, a 68-year-old woman (half sister of the patient in case 1) experienced difficulty in swallowing at age 63 and developed speech difficulty and finger weakness at age 65. Dysphagia and dysarthria progressed gradually until three months before hospital admission. After developing dyspnoea and somnolence, she was admitted to the hospital. Because of her respiratory dysfunction type 2 (PaO2 50.5 mmHg, PaCO2 76.7 mmHg) diagnosis, she was treated with non-invasive positive pressure ventilation. Neurological examination showed dysphagia and nasal voice, despite there being no obvious facial weakness or tongue atrophy. Wasting was observed in the bilateral thenar, hypothenar, and first dorsal interossei muscles without fasciculation. The muscle weakness decreased moderately in the wrist extensors, iliopsoas, and extensor hallucis longus muscles and mildly in the deltoid, hamstring, and tibialis anterior muscles. Touch, pinprick, vibration, and position sensations remained intact but slight dysesthesia was present in the toe tips. Tendon reflexes were absent, except of a markedly decreased patella tendons reflex. Both cases of the patients did not fulfil diagnostic criteria of ALS because they lacked upper motor neurone signs. After obtaining informed consent from patients and approval from a local ethics committee, genomic DNA was extracted from the peripheral blood samples for both patients. We conducted exome-sequencing to determine

Mitochondrial myopathy with autophagic vacuoles in patients with the m.8344A>G mutation

Background and aims In mitochondrial myopathy, autophagy is presumed to play an important role in mitochondrial dysfunction. Rimmed vacuoles (RVs), a sign of autophagy, can be seen as a secondary phenomenon in muscle ragged-red fibres (RRFs), whereas the uncommon presentation is that some fibres contain RVs, but without any mitochondrial abnormalities. To investigate the pathogenesis beneath this pathological phenomenon. Methods We reviewed 783 skeletal muscle specimens and selected five obtained from patients with suspected mitochondrial myopathy, characterised by clearly visible autophagic vacuoles in non-RRFs, besides the coexistence of RRFs and cytochrome oxidase-negative fibres. Immunohistochemical staining with LC-3, and electron microscopy studies were performed. Using resequencing microarray and a next-generation sequencing system, the mitochondrial DNA was screened for mutations and the heteroplasmic level was measured in skeletal muscle and blood. Results Muscle fibres with RVs and RRFs, as well as some morphologically normal fibres, stained strongly for LC-3. Electron microscopy disclosed significant abnormal mitochondrial proliferation and existence of autophagic vacuoles. After mutation screening, m.8344A>G in the tRNALys gene was detected in two patients. The heteroplasmy of mutated G was 45.1% in skeletal muscle and 17.8% in blood in patient 1; patient 2 exhibited 80.3% mutated G in skeletal muscle and 25.2% in blood. Conclusions These findings demonstrate a new pathological phenotype for the m.8344A>G mutation- related disease and also provide pathological evidence of a correlation between mitochondrial abnormalities and autophagy.

Neuron-specific knockdown of the Drosophila fat induces reduction of life span, deficient locomotive ability, shortening of motoneuron terminal branches and defects in axonal targeting

Mutations in FAT4 gene, one of the human FAT family genes, have been identified in Van Maldergem syndrome (VMS) and Hennekam lymphangiectasia‐lymphedema syndrome (HS). The FAT4 gene encodes a large protein with extracellular cadherin repeats, EGF‐like domains and Laminin G‐like domains. FAT4 plays a role in tumor suppression and planar cell polarity. Drosophila contains a human FAT4 homologue, fat. Drosophila fat has been mainly studied with Drosophila eye and wing systems. Here, we specially knocked down Drosophila fat in nerve system. Neuron‐specific knockdown of fat shortened the life span and induced the defect in locomotive abilities of adult flies. In consistent with these phenotypes, defects in synapse structure at neuromuscular junction were observed in neuron‐specific fat‐knockdown flies. In addition, aberrations in axonal targeting of photoreceptor neuron in third‐instar larvae were also observed, suggesting that fat involves in axonal targeting. Taken together, the results indicate that Drosophila fat plays an essential role in formation and/or maintenance of neuron. Both VMS and HS show mental retardation and neuronal defects. We therefore consider that these two rare human diseases could possibly be caused by the defect in FAT4 function in neuronal cells.

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.

Adult‐onset Krabbe disease presenting with an isolated form of peripheral neuropathy

Introduction: Adult‐onset Krabbe disease is clinically rare and usually affects the pyramidal tracts in the central nervous system. Patients develop a spastic gait, and peripheral neuropathy sometimes occurs simultaneously. Methods: A 55‐year‐old woman with consanguineous parents developed slowly progressive, asymmetric muscle weakness and atrophy in her forearms, while her ability to walk remained unaffected without pyramidal tract signs after onset at age 51 years. Results: Nerve conduction studies demonstrated an asymmetric demyelinating‐type peripheral neuropathy, and sural nerve biopsy documented reduced myelinated nerve fiber density with uniformly thin myelin sheaths, suggesting hypomyelination. Brain MRI demonstrated minor white‐matter injury along the optic radiations, which was associated with asymptomatic, mild, prolonged latency on visual evoked potentials. Laboratory analysis documented low enzyme activity of galactocerebrosidase (GALC) and a known mutation of the GALC gene. Conclusion: Isolated peripheral neuropathy occurs very rarely in adult‐onset Krabbe disease. Muscle Nerve 54: 152–157, 2016

New type of encephalomyelitis responsive to trimethoprim/sulfamethoxazole treatment in Japan

Objective: To determine the causative pathogen and investigate the effective treatment of a new type of encephalomyelitis with an unknown pathogen in Japan and report the preliminary ultrastructural and genomic characterization of the causative agent. Methods: From 2005 to 2012, we treated 4 Japanese patients with geographic clustering and comparable clinical features, serum/CSF cytology, and radiologic findings. Brain biopsy was conducted in all patients to analyze neuropathologic changes by histology, and electron microscopy was applied to reveal the features of the putative pathogen. Genomic DNA was obtained from the affected brain tissues and CSF, and an unbiased high-throughput sequencing approach was used to screen for specific genomic sequences indicative of the pathogen origin. Results: All patients exhibited progressive dementia with involuntary tongue movements. Cytologic examination of CSF revealed elevated mononuclear cells. Abnormal MRI signals were observed in temporal lobes, subcortical white matter, and spinal cord. Biopsied brain tissue exhibited aggregated periodic acid-Schiff–positive macrophages and 2–7 μm diameter round/oval bodies without nuclei or cell walls scattered around the vessels. Unbiased high-throughput sequencing identified more than 100 archaea-specific DNA fragments. All patients were responsive to trimethoprim/sulfamethoxazole (TMP-SMX) plus corticosteroid therapy. Conclusions: We report 4 cases of encephalomyelitis due to an unknown pathogen. On the basis of ultrastructural and genomic studies, we propose a new disease entity resulting from a causative pathogen having archaeal features. TMP-SMX therapy was effective against this new type of encephalomyelitis.