The TRK-fused gene is mutated in hereditary motor and sensory neuropathy with proximal dominant involvement

Hereditary motor and sensory neuropathy with proximal dominant involvement (HMSN-P) is an autosomal-dominant neurodegenerative disorder characterized by widespread fasciculations, proximal-predominant muscle weakness, and atrophy followed by distal sensory involvement. To date, large families affected by HMSN-P have been reported from two different regions in Japan. Linkage and haplotype analyses of two previously reported families and two new families with the use of high-density SNP arrays further defined the minimum candidate region of 3.3 Mb in chromosomal region 3q12. Exome sequencing showed an identical c.854C>T (p.Pro285Leu) mutation in the TRK-fused gene (TFG) in the four families. Detailed haplotype analysis suggested two independent origins of the mutation. Pathological studies of an autopsied patient revealed TFG- and ubiquitin-immunopositive cytoplasmic inclusions in the spinal and cortical motor neurons. Fragmentation of the Golgi apparatus, a frequent finding in amyotrophic lateral sclerosis, was also observed in the motor neurons with inclusion bodies. Moreover, TAR DNA-binding protein 43 kDa (TDP-43)-positive cytoplasmic inclusions were also demonstrated. In cultured cells expressing mutant TFG, cytoplasmic aggregation of TDP-43 was demonstrated. These findings indicate that formation of TFG-containing cytoplasmic inclusions and concomitant mislocalization of TDP-43 underlie motor neuron degeneration in HMSN-P. Pathological overlap of proteinopathies involving TFG and TDP-43 highlights a new pathway leading to motor neuron degeneration.

Late-onset Charcot-Marie-Tooth disease 4F caused by periaxin gene mutation

We identified the main features of Charcot-Marie-Tooth (CMT) disease, type 4F, caused by a periaxin gene (PRX) mutation in Japanese patients. Periaxin is known as one of the key myelination molecules, forming tight junction between myelin loop and axon. We collected 427 DNA samples from individuals with CMT or CMT-related neuropathy, negative for PMP22 duplication. We investigated PRX mutations using a purpose-built resequencing array screen during the period 2006-2012. We detected two types of PRX mutations in three patients; one patient showed a novel homozygous p.D651N mutation and the other two showed homozygous p.R1070X mutation. All PRX mutations reported so far have been of nonsense or frameshift type. In this study, we found homozygous missense mutation p.D651N. Aspartate 651 is located in a repeat domain; its position might indicate an important function. PRX mutations usually lead to early-onset, autosomal-recessive demyelinating CMT neuropathy 4F (CMT4F) or Dejerine-Sottas disease; their clinical phenotypes are severe. In our three patients, the onset of the disease was at the age of 27 years or later, and their clinical phenotypes were milder compared with those reported in previous studies. We showed a variation of clinical phenotypes for CMT4F caused by a novel, nonsense PRX mutation.

Coenzyme Q10 therapy in hereditary motor sensory neuropathy type VI with novel mitofusin 2 mutation

Hereditary motor sensory neuropathy type VI (HMSN VI) is hereditary neuropathy accompanied by optic neuropathy. The feasibility of Coenzyme Q10 (CoQ10) as a treatment for subacute visual impairment of HMSN VI was examined. A 37-year-old patient with HMSN VI with a novel mitofusin 2 mutation was treated with high dose of CoQ10 (200 mg/day) for eight months. Visual impairment was partially resolved after CoQ10 therapy. High dose CoQ10 therapy may improve the prognosis of subacute visual impairment in HMSN VI. To confirm the effectiveness of CoQ10 on HMSN VI, further studies are needed.

Reduced penetrance in hereditary motor neuropathy caused by TRPV4 Arg269Cys mutation

Incomplete penetrance has rarely been reported in Charcot-Marie-Tooth disease. Our aim is to describe reduced penetrance in a hereditary motor neuropathy pedigree due to mutation in the transient receptor potential vallinoid 4 (TRPV4) gene. The pedigree comprised two affected members, the proband aged 44 years and her affected daughter aged 7 years, and seven additional related subjects, three of whom were subclinical gene mutation carriers aged 9, 40 and 70 years. Clinico-electrophysiological studies, MRI of lower-limb musculature and genetic testing of the TRPV4 were performed. The proband presented with a moderate facio-scapulo-peroneal syndrome, whereas her symptomatic daughter suffered from severe congenital spinal muscular atrophy with arthrogryposis, laryngomalacia, and vocal cord paresis. Electrophysiological evaluation revealed a pure motor axonal neuropathy. In the proband, MRI showed extensive and widespread fatty atrophy of lower-leg musculature, whereas in thigh musculature there was just mild distal fatty infiltration of vastus lateralis. Genetic testing revealed a heterozygous Arg269Cys mutation in the TPRV4 gene. In all three mutation carriers results from clinical and electrophysiological examination, and MRI of foot and lower-leg musculature were normal. We conclude that non-penetrance may be an integral feature of neuropathic syndromes associated with TRPV4 gene mutation.

[Clinical-genetic correlations in the hereditary motor-sensor neuropathy caused by mutations in the MPZ (P0) gene]

Hereditary motor-sensor neuropathy (HMSN) caused by mutations in the MPZ (P0) gene is a rare variant of hereditary demyelinating polyneuropathies that makes up 5-10% of all cases in different populations. Based on the complex examination of patients of the Russian Federation with different MPZ (P0) mutations, we obtained clinical-genetic, electromyographic and molecular-genetic characteristics of HMSN caused by mutations in the MPZ (P0) gene. Peculiarities of clinical presentations in patients with HMSN, types 1B and 2I, are presented. Diagnostic criteria of these genetic variants have been formed. The new allelic variants of HMSN caused by mutations in the MPZ (P0) gene are described. The distribution of mutations by protein domains has been analyzed.

[Molecular pathogenesis of hereditary motor and sensory neuropathy]

Charcot-Marie-Tooth disease 2 is an inherited axonal motor and sensory neuropathy. It is very heterogenous, both clinically and genetically. Till present, 15 types of CMT2, 14 loci and 13 genes are known to be causative of CMT2. Studying mechanisms of molecular pathogenesis is very important for finding a therapy for patients but the diversity of proteins involved in pathogenesis makes this very difficult. Proteins involved in molecular pathogenesis are e.g. proteins of the mitochondrial outer membrane with opposite functions (mitofusin 2 and GDAP1) responsible for fusion and fission of the mitochondrial network. Mutations also occur in genes encoding tRNA-synthetases, neuronal cytoskeletal protein, cation channel protein and molecular chaperones. This review presents knowledge of CMT2 and possible pathogenetic mechanisms responsible for the disease.

[Hereditary motor and sensory neuropathy type 4A]

The first in the Russian Federation clinical cases of patients with autosomal-recessive type of hereditary motor and sensory neuropathy, type 4A, (HMSN 4A) are presented. In all cases, the diagnosis has been verified using molecular-genetic methods (DNA diagnostics). An analysis of features of clinical manifestations was performed in patients, aged from 5 to 34 years, with different disease duration (from 3-to 29 years). Criteria of selection of patients for DNA diagnostics for searching mutations in the GDAP1 gene are specified.

[Hereditary motor and sensory neuropathy type 4A]

The first in the Russian Federation clinical cases of patients with autosomal-recessive type of hereditary motor and sensory neuropathy, type 4A, (HMSN 4A) are presented. In all cases, the diagnosis has been verified using molecular-genetic methods (DNA diagnostics). An analysis of features of clinical manifestations was performed in patients, aged from 5 to 34 years, with different disease duration (from 3-to 29 years). Criteria of selection of patients for DNA diagnostics for searching mutations in the GDAP1 gene are specified.

A newly identified Thr99fsX110 mutation in the PMP22 gene associated with an atypical phenotype of the hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is manifested by a spectrum of phenotypes, from the classical HNPP course associated with intermittent nerve palsies to a neuropathy resembling Charcot-Marie-Tooth type 1 (CMT1) disease. The majority of HNPP cases are associated with submicroscopical deletions in the 17p11.2-p12 region containing the PMP22 gene, while PMP22 point mutations are rare, representing about 15% of HNPP cases. In this study, we present a patient manifesting with atypical HNPP phenotype associated with a new Thr99fsX110 mutation in the PMP22 gene. We conclude that all patients who fulfill the electrophysiological criteria of HNPP, even if they lack the typical HNPP phenotype, should be tested for point mutations in the PMP22 gene.

The genetics of motor neuron diseases

Motor neuron diseases may be divided into three categories: those with lower motor neuron involvement--spinal muscular atrophy (SMA) and spinobulbar muscular atrophy (SBMA or Kennedy's disease); those with upper motor neuron involvement--primary lateral sclerosis (PLS) and the spastic paraplegias; and those with combined upper and lower motor neuron involvement--amyotrophic lateral sclerosis (ALS). Other familial motor neuron disorders include hereditary neuronopathies, GM2 gangliosidosis, and possibly the ALS/PD syndrome of Guam. The contribution of genetics to the etiopathogenesis of motor neuron considerably, accounting for a high percentage of spinal muscular atrophies, but only a small fraction of cases of ALS. The mode of inheritance also varies, with examples of autosomal dominant (AD), autosomal recessive (AR), or X-linked kindreds. (Tables 1 and 2).

Analysis of 17p11.2 chromosome region rearrangements in CMT1 patients from Ukraine

Two intercomplementary methods of 17p11.2 duplication/deletion identification have been elaborated: STR allelic variants analysis and direct PMP22 gene dosage measuring by means of quantitative Real- Time PCR. It has been carried out detection and analysis of 17p11.2 chromosome region rearrangements in CMT1 patients from Ukraine. It has been registered the high level of de novo cases with 17p11.2-duplication. It has been shown the 17p11.2 chromosome region duplication/deletion association with CMT1A and HNPP clinical phenotypes which may be used in differential diagnosis of this type of CMT polyneuropathy.

Hereditary neuropathy with liability to pressure palsy in childhood

HNPP is an autosomal-dominant inherited disease clinically characterized by painless, episodic, recurrent peripheral palsy often preceded by minor trauma or toxic damage. It generally develops during adolescence and rarely is reported in childhood. We observed two children with this disease. In one of the cases, also the child's mother is suffering from HNPR Clinical and genetic characteristics of our three patients are summarized in this article.

[Screening for hereditary neuromuscular disorders with molecular genetic methods in the Roma population of Hungary]

Recent medical genetic research has identified a number of novel, or previously known, but rare conditions, caused by private founder mutations. The Finnish and Ashkenazi Jew populations provide the best examples for identifying genes in unique genetic disorders. In these populations, research efforts and high-level medical services resulted in intense improvements of medical care and in organization of population-based screening programs. Hereditary disorders of the Roma populations are known for a long time. The genetic background of these diseases has been established by extensive molecular genetic studies. The Romas represent 6% of the Hungarian population and live under extremely bad health conditions. Therefore, our aim was to map the incidence of the hereditary neuromuscular disorders among the Hungarian Roma population. Moreover, we intended to provide proper information, genetic counseling and possible prevention strategies for the families at risk, which should represent a primer task in public health. Because of our experience in neuromuscular disorders, we choose six, frequent, autosomal recessive disorders for these clinical and genetic studies: hereditary motor and sensory neuropathy type Lom (HMSNL), hereditary motor and sensory neuropathy type Russe (HMSNR), congenital cataracts facial dysmorphism syndrome (CCFDN), limb-girdle muscular dystrophy 2C (LGMD2C), congenital myasthenic syndrome (CMS) and spinal muscular atrophy (SMA). Following identification of the founder mutations, the possibility of prenatal diagnosis and carrier screening for family members will contribute to the decrease of the recurrence risk for these severe, mostly untreatable disorders.

Molecular mechanisms of inherited demyelinating neuropathies

The past 15 years have witnessed the identification of more than 25 genes responsible for inherited neuropathies in humans, many associated with primary alterations of the myelin sheath. A remarkable body of work in patients, as well as animal and cellular models, has defined the clinical and molecular genetics of these illnesses and shed light on how mutations in associated genes produce the heterogeneity of dysmyelinating and demyelinating phenotypes. Here, we review selected recent developments from work on the molecular mechanisms of these disorders and their implications for treatment strategies.

Hereditary motor and sensory neuropathy Lom type in a Serbian family

Hereditary motor and sensory neuropathy Lom type (HMSNL), also called CMT 4D, a hereditary autosomal recessive neuropathy, caused by mutation in N-Myc downstream regulated gene 1 (NDRG1 gene), was first described in a Bulgarian Gypsy population near Lom and later has been found in Gypsy communities in Italy, Spain, Slovenia and Hungary. We present two siblings with HMSNL, female and male, aged 30 and 26, respectively in a Serbian non-consanguineous family of Gypsy ethnic origin. They had normal developmental milestones. Both had symptoms of lower limb muscle weakness and walking difficulties with frequent falls, which began at the age of seven. At the age of 12, they developed hearing problems and at the age of 15 hand muscle weakness. Neurological examination revealed sensorineural hearing loss, dysarthria, severe distal and mild proximal muscle wasting and weakness, areflexia and impairment of all sensory modalities of distal distribution. Electrophysiological study revealed denervation with severe and early axonal loss. Sensorineural hearing loss was confirmed on electrocochleography and brainstem evoked potentials. Molecular genetic testing confirmed homozygote C564t (R148X) mutation in NDRG1 gene.

Experimental therapeutics in hereditary neuropathies: the past, the present, and the future

Hereditary neuropathies represent approximately 40% of undiagnosed neuropathies in a tertiary clinic setting. The Charcot-Marie-Tooth neuropathies (CMT) are the most common. Mutations in more than 40 genes have been identified to date in CMT. Approximately 50% of CMT cases are accounted for by CMT type 1A, due to a duplication within the peripheral myelin protein 22 gene (PMP22). Mutations in the gap junction beta 1 gene (GJB1), the myelin protein zero gene (MPZ), and the mitofusin 2 gene (MFN2) account for a substantial proportion of other genetically definable CMT. Some 15% of demyelinating CMT and 70% of axonal CMT await genetic clarification. Other hereditary neuropathies include the hereditary sensory and autonomic neuropathies, the familial amyloid polyneuropathies, and multisystem disorders (e.g., lipid storage diseases and inherited ataxias) that have peripheral neuropathy as a major or minor component. This review surveys the challenges of developing effective therapies for hereditary neuropathies in terms of past, present, and future experimental therapeutics in CMT.

Homozygosity for the transthyretin-Met30-gene in seven individuals with familial amyloidosis with polyneuropathy detected by restriction enzyme analysis of amplified genomic DNA sequences

Familial amyloidotic polyneuropathy (FAP) with a mutation in position 30 of transthyretin (TTR) (previously called prealbumin) is an autosomal dominant inherited disorder characterized by varying degrees of peripheral neuropathy, nephropathy, gastrointestinal problems, and vitreous amyloid. We have earlier diagnosed homozygosity for the TTR-Met30-gene using Southern analysis in four Swedish individuals. We have found it possible to detect homozygosity for the Met-30 mutation by amplifying discrete regions of the TTR-gene using polymerase chain reaction (PCR), and the amplification products restricted with NsiI analysed by gel electrophoresis. Clinical data on seven homozygous individuals, including three new cases, are presented.

Painful brachial plexopathies in SEPT9 mutations: adverse outcome related to comorbid states

Hereditary neuralgic amyotrophy (HNA), an autosomal dominant disorder associated with SEPT9 mutation located on chromosome 17q25, causes recurrent painful weakness with sensory disturbances in a brachial distribution. We present electrophysiological, clinical phenotype, and molecular genetic data of three members from a family with HNA with the C262T SEPT9 mutation. The degree of motor weakness and recovery is variable within this family. Severity and recovery from motor deficits may have been a function of comorbid medical conditions. To our knowledge, this is the first report to confirm SEPT9 mutation in a family with suspected HNA.