Coexistence of Charcot-Marie-Tooth 1A and nondystrophic myotonia due to PMP22 duplication and SCN4A pathogenic variants: a case report.

BACKGROUND: Charcot-Marie-Tooth disease (CMT) is a genetically heterogeneous hereditary neuropathy, and CMT1A is the most common form; it is caused by a duplication of the peripheral myelin protein 22 (PMP22) gene. Mutations in the transient sodium channel Nav1.4 alpha subunit (SCN4A) gene underlie a diverse group of dominantly inherited nondystrophic myotonias that run the spectrum from subclinical myopathy to severe muscle stiffness, disabling weakness, or frank episodes of paralysis. CASE PRESENTATION: We describe a Chinese family affected by both CMT1A and myotonia with concomitant alterations in both the PMP22 and SCN4A genes. In this family, the affected proband inherited the disease from his father in an autosomal dominant manner. Genetic analysis confirmed duplication of the PMP22 gene and a missense c.3917G > C (p. Gly1306Ala) mutation in SCN4A in both the proband and his father. The clinical phenotype in the proband showed the combined involvement of skeletal muscle and peripheral nerves. Electromyography showed myopathic changes, including myotonic discharges. MRI revealed the concurrence of neurogenic and myogenic changes in the lower leg muscles. Sural nerve biopsies revealed a chronic demyelinating and remyelinating process with onion bulb formations in the proband. The proband's father presented with confirmed subclinical myopathy, very mild distal atrophy and proximal hypertrophy of the lower leg muscles, pes cavus, and areflexia. CONCLUSION: This study reports the coexistence of PMP22 duplication and SCN4A mutation. The presenting features in this family suggested that both neuropathy and myopathy were inherited in an autosomal dominant manner. The proband had a typical phenotype of sodium channel myotonia (SCM) and CMT1A. However, his father with the same mutations presented a much milder clinical phenotype. Our study might expand the genetic and phenotypic spectra of neuromuscular disorders with concomitant mutations.

Clinicopathological features in two families with MARS-related Charcot-Marie-Tooth disease.

Mutations in MARS gene cause dominant Charcot-Marie-Tooth disease (CMT) 2U. The aim of this study is to investigate phenotypic heterogeneities and peripheral neuropathology of MARS-related CMT patients. We identified a heterozygous p. R199Q mutation and an already reported heterozygous p. P800T mutation of MARS gene in two unrelated families using targeted next-generation sequencing. The first pedigree comprised three patients over three generations and the second pedigree comprised two patients over two generations. In addition of an asymptomatic carrier in the second pedigree, all patients presented with childhood-onset length dependent sensorimotor neuropathy with pes cavus. Nerve conduction studies revealed slowing of motor nerve conduction velocities (MNCV) of the median nerve indicating intermediate neuropathy in the patient with the p. R199Q mutation, and normal MNCV with reduced compound muscle action potential indicating axonal neuropathy in the patient with the p. P800T mutation. Magnetic resonance imaging detected a pattern of nerve changes similar to those in demyelinating polyneuropathies in intermediate type (p. R199Q mutation) patients compared with normal in the axonal type (p. P800T mutation) patients. Additionally, sural nerve biopsy revealed loss of myelinated axons with onion bulb formation in both mutations. By electron microscopy, a marked decrease of myelinated and unmyelinated fiber, neurofilaments aggregate with degenerating mitochondria and microtubule loss in axons were frequently found. Denervated Schwann cell complexes and few collagen pockets indicated involvement of unmyelinated Schwann cells. Therefore, the investigated MARS mutations cause not only the known axonal type but also intermediate type neuropathy with involvement of both axons and Schwann cells. Those findings are useful for the differential diagnosis of CMT patients with unknown MARS variants.

A de novo variant of POLR3B causes demyelinating Charcot-Marie-Tooth disease in a Chinese patient: a case report.

BACKGROUND: Charcot-Marie-Tooth (CMT) disease is a group of inherited peripheral neuropathies, which are subdivided into demyelinating and axonal forms. Biallelic mutations in POLR3B are the well-established cause of hypomyelinating leukodystrophy, which is characterized by hypomyelination, hypodontia, and hypogonadotropic hypogonadism. To date, only one study has reported the demyelinating peripheral neuropathy phenotype caused by heterozygous POLR3B variants. CASE PRESENTATION: A 19-year-old male patient was referred to our hospital for progressive muscle weakness of the lower extremities. Physical examination showed muscle atrophy, sensory loss and deformities of the extremities. Nerve conduction studies and electromyography tests revealed sensorimotor demyelinating polyneuropathy with secondary axonal loss. Trio whole-exome sequencing revealed a de novo variant in POLR3B (c.3137G > A). CONCLUSIONS: In this study, we report the case of a Chinese patient with a de novo variant in POLR3B (c.3137G > A), who manifested demyelinating CMT phenotype without additional neurological or extra-neurological involvement. This work is the second report on POLR3B-related CMT.

Sural biopsy to detect the axonal cytoskeleton defects in KIF5A-related Charcot-Marie-Tooth disease type 2.

Kinesins are microtubule-associated motor proteins involved in in regulating microtubule dynamics in neuronal and non-neuronal cells. However, the axonal cytoskeleton-related pathological changes in peripheral nerve have never been described in patients with KIF5A mutation. This study aims to report sural biopsy to detect axonal cytoskeleton abnormalities in a patient with KIF5A-related Charcot-Marie-Tooth disease type 2 (CMT2). We screened for the variants of CMT or related pathogenic genes using next-generation sequencing in a Chinese family with CMT2. The proband was a 13-year-old girl who presented with severe weakness and wasting of distal muscles of limbs starting at early childhood. The disease rapidly progressed, and the girl lost ambulation. Her mother showed absence of deep tendon reflexes in the lower limbs. Nerve conduction studies disclosed a more pronounced axonal sensory-motor neuropathy in the proband. The girl and her mother had a heterozygous p.E755K mutation of the KIF5A gene, which was previously reported only in hereditary spastic paraplegia and amyotrophic lateral sclerosis. Sural biopsy revealed loss of both myelinated and unmyelinated nerve fibers. Closely packed, irregularly oriented neurofilaments were observed in axons of unmyelinated nerve fibers. Another important finding was ubiquitous presence of elongated mitochondria with vacuole in the myelinated and unmyelinated axons. This study suggested the p.E755K mutation of KIF5A was a cause of early-onset CMT2 with defective axonal transport, and emphasized sural biopsy could be an important tool to detect axonal cytoskeleton defects in KIF5A related CMT2.

PLEKHG5-related autosomal recessive lower motor neuron disease with dysmyelination in peripheral nerves.

OBJECTIVE: Pleckstrin homology domain-containing family G member 5 (PLEKHG5) is a nuclear factor-κ-B-activator gene that predominantly expresses in the neurons and Schwann cells of the peripheral nervous system. Variations in the PLEKHG5 have shown an intermediate form of autosomal recessive Charcot-Marie-Tooth disease and lower motor neuron disease in childhood. MATERIALS AND METHODS: This study investigated clinically, electrophysiologically, genetically, and pathologically a young girl with lower motor neuron disease who had weakness and wasting of all limbs starting in early childhood. RESULTS: Next-generation sequencing found a novel compound heterozygous missense variation c.2038-1G>A and c.1219G>T of PLEKHG5 gene. Electromyography revealed a neurogenic pattern, and nerve conduction study indicated subclinical sensory neuropathy. Sural biopsy showed hypomyelination, hypermyelination, and infolding myelin membranes coiled into the myelinated axon. CONCLUSION: This study identifies, pathologically, novel compound heterozygous mutations and phenotype in PLEKHG5-related lower motor neuron disease and dysmyelination in a patient with PLEKHG5 mutation.

A novel mutation in PRPS1 causes X-linked Charcot-Marie-Tooth disease-5.

X-linked Charcot-Marie-Tooth disease-5 (CMTX5) is a rare hereditary disorder caused by mutations in the gene for phosphoribosyl pyrophosphate synthetase-1 (PRPS1). We investigated a boy with a novel PRPS1 mutation (c.334G>C, p.V112L) via genetic, neuropathological and enzymatic tests. The proband was a 13-year-old boy with congenital non-syndromic sensorineural deafness. At 3 year old, he developed progressive distal weakness of all limbs with muscle atrophy of both hands and shanks. Nerve conduction study revealed the loss of sensory nerve action potentials, and slowing down of motor nerve conduction velocities with a decrease of amplitudes of compound motor action potentials. Visual evoked potentials and brainstem auditory evoked potentials were not bilaterally evocable. Sural biopsy proved the loss of myelinated nerve fibers, with axonal degeneration, regenerating clusters and onion bulbs. Enzymatically, PRPS1 activity was close to zero in the proband and mildly reduced in his mother, compared with controls. To our knowledge, this is the first report of CMTX5 in a Chinese population. The genetic finding has expanded the genotypic spectrum of PRPS1 mutations.

HADHB mutations cause infantile-onset axonal Charcot-Marie-Tooth disease: A report of two cases.

Mitochondrial trifunctional protein deficiency (MTPD) is a rare disorder caused by mutations in the HADHA and HADHB genes. Here, we report on two Han Chinese patients with HADHB mutation-associated infantile axonal Charcot-Marie-Tooth disease (IACMT). Both patients were unrelated. Case 1 was a 19-year-old man, and case 2 was a 5-year-old boy. Both had delayed motor development and slowly-progressing distal muscle weakness with areflexia and foot deformities. The electrophysiology findings were compatible with axonal polyneuropathy in both patients. Blood tandem mass spectrometry showed increased concentrations of multiple acylcarnitines. Nerve biopsies showed axonal neuropathy with a moderate loss of myelinated fibers. Gene analysis identified two compound heterozygous mutations (c.184A>G/c.340A>G and c.488G>A/c.1175C>T, respectively) in the HADHB gene. The c.488G>A mutation was novel. This study broadens the phenotype of MTPD and suggests that the genetic testing of patients suffering from IACMT should include the HADHB gene.
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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.

Evaluation of the median nerve by shear wave elastography in patients with Charcot-Marie-Tooth disease type 1A.

AIMS: Charcot-Marie-Tooth disease type 1A (CMT1A) is characterized by enlargement and stiffness of peripheral nerves due to edema with large numbers of "onion bulbs" in the endoneurium. Ultrasound elastography seems to be an ideal method to detect this condition. The aim of this study was to analyze the shear wave elastography (SWE) features of peripheral nerves in patients with CMT1A. MATERIAL AND METHODS: We included 24 CMT1A patients with a mean age of 28 years, along with 24 age- and gender-matched controls. All patients presented with mutations of the PMP22 gene and showed length-dependent polyneuropathy. The motor nerve conduction velocity (MNCV) of the median nerve ranged from 5.2 to 37.4 m/s. SWE and cross-sectional area (CSA) were used to evaluate the bilateral median nerves at predefined sites in both patients and con-trols. RESULTS: The average elastography value (EV) of the median nerve was 73.5±11.7 kPa in patients with CMT1A and 37.5±6.1 kPa in control subjects. The difference between the two groups was statistically significant (P<0.05). In CMT1A pa-tients, the average EV at the proximal and distal parts of the median nerve were 81.4±9.4 kPa and 65.2±8.1 kPa, respectively. The average CSAs at the proximal and distal parts of the median nerve were 0.29±0.06 cm2 and 0.20±0.05 cm2, respectively. The EV on SWE was positively correlated with CSA (p< 0.01) and negatively correlated with MNCV in the median nerve (p< 0.01). CONCLUSIONS: Peripheral nerve stiffness dramatically increases in CMT1A and is correlated with the severity of nerve involvement.

Pathogenic PSAT1 Variants and Autosomal Recessive Axonal Charcot-Marie-Tooth Disease With Ichthyosis.

BACKGROUND: Biallelic pathogenic phosphoserine aminotransferase 1 (PSAT1) variants generally cause a severe phenotype predominantly involving the central nervous system. Here, for the first time, we report two patients harboring pathogenic PSAT1 variants only manifested as polyneuropathy and ichthyosis. METHODS: Two patients from unrelated families presenting with polyneuropathy and ichthyosis were enrolled. Whole exome sequencing was performed to identify possible disease-causing variants. Their clinical, electrophysiological, imaging, biochemical, and pathologic changes were in detail assessed and investigated. RESULTS: Homozygous variant c.43G>C and compound heterozygous variants c.112A>C and c.43G>C in PSAT1 were identified in patients 1 and 2, respectively. Nerve conduction studies revealed preserved or mild slowing motor nerve conduction velocities of the median nerves in the two patients, whereas the compound motor action potential in patient 1 was severely decreased. Brain magnetic resonance imaging of the two patients found no abnormalities. Median nerve enlargement was observed on ultrasound in patient 1. Both patients had normal level of serine and glycine in plasma and cerebrospinal fluid. Sural nerve biopsy found severe loss of myelinated fibers. Electron microscopy revealed neurofilament accumulation and mitochondrial aggregation in axons. Both variants in PSAT1 were classified as likely pathogenic or pathogenic variants according to the standard guidelines. CONCLUSIONS: Our study confirms that pathogenic PSAT1 variants can cause a mild phenotype, predominantly as autosomal recessive axonal Charcot-Marie-Tooth disease.