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The Charcot-Marie-Tooth (CMT) disorders comprise a group of clinically and genetically heterogeneous hereditary motor and sensory neuropathies, which are mainly characterized by muscle weakness and wasting, foot deformities, and electrophysiological, as well as histological, changes. A subtype, CMT2, is defined by a slight or absent reduction of nerve-conduction velocities together with the loss of large myelinated fibers and axonal degeneration. CMT2 phenotypes are also characterized by a large genetic heterogeneity, although only two genes---NF-L and KIF1Bbeta---have been identified to date. Homozygosity mapping in inbred Algerian families with autosomal recessive CMT2 (AR-CMT2) provided evidence of linkage to chromosome 1q21.2-q21.3 in two families (Zmax=4.14). All patients shared a common homozygous ancestral haplotype that was suggestive of a founder mutation as the cause of the phenotype. A unique homozygous mutation in LMNA (which encodes lamin A/C, a component of the nuclear envelope) was identified in all affected members and in additional patients with CMT2 from a third, unrelated family. Ultrastructural exploration of sciatic nerves of LMNA null (i.e., -/-) mice was performed and revealed a strong reduction of axon density, axonal enlargement, and the presence of nonmyelinated axons, all of which were highly similar to the phenotypes of human peripheral axonopathies. The finding of site-specific amino acid substitutions in limb-girdle muscular dystrophy type 1B, autosomal dominant Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy type 1A, autosomal dominant partial lipodystrophy, and, now, AR-CMT2 suggests the existence of distinct functional domains in lamin A/C that are essential for the maintenance and integrity of different cell lineages. To our knowledge, this report constitutes the first evidence of the recessive inheritance of a mutation that causes CMT2; additionally, we suggest that mutations in LMNA may also be the cause of the genetically overlapping disorder CMT2B1.
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PMID:Homozygous defects in LMNA, encoding lamin A/C nuclear-envelope proteins, cause autosomal recessive axonal neuropathy in human (Charcot-Marie-Tooth disorder type 2) and mouse. 1179 77

Three Spanish families with an autosomal recessive severe hereditary motor and sensory neuropathy, showing mutations in the ganglioside-induced-differentiation-associated protein 1 (GDAP1) gene in the Charcot-Marie-Tooth (CMT) type 4A locus were studied. The disorder started in the neonatal period or early infancy with weakness and wasting of the feet and, subsequently, involvement of the hands, causing severe disability. By the late teens, some patients developed a hoarse voice and vocal cord paresis. Peripheral motor nerve conduction velocity (MNCV) could not be measured in many cases because of the absence of muscle response due to distal atrophy. However, latencies to proximal muscles were in the normal range; median MNCV was >40 m/s in those cases in which it could be measured. Sural nerve biopsy from two patients showed a pronounced depletion of myelinated fibres, regenerative clusters and signs of axonal atrophy. Additionally, a small proportion of thin myelinated fibres and proliferation of Schwann cells forming onion bulb structures were also found. Unmyelinated fibre population was markedly increased. These findings are indicative of a predominant axonal degeneration with some demyelinating features. These Spanish families share in the severe CMT clinical phenotype with some Tunisian families who also presented mutations in the GDAP1 gene and to which the CMT4A locus was originally assigned. However, our families differ in the presence of laryngeal involvement and values of MNCV and pathological features are more in line with CMT2 type. The possibility that GDAP1 gene mutations could be expressed under different phenotypes is a question to be resolved.
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PMID:Clinical, electrophysiological and morphological findings of Charcot-Marie-Tooth neuropathy with vocal cord palsy and mutations in the GDAP1 gene. 1282 18

Charcot-Marie-Tooth disease is a clinically and genetically heterogeneous group of inherited neuropathies. The common clinical symptoms include distal muscle weakness, wasting and impaired distal sensation, more in the legs than in the arms, and reduced or absent reflexes. Moreover, foot and hand deformities are often encountered. A distinction between a primarily demyelinating or axonal neuropathy is often possible by means of nerve conduction studies. The major groups of inheritance are the autosomal dominant CMT1 (demyelinating), CMT2 (axonal) and the X-linked type (CMTX), but there are also autosomal recessive demyelinating (CMT4) and axonal (AR-CMT2) forms. The number of genes and loci is steadily increasing, with genes encoding proteins involved in myelin maintenance and axonal function, but also with genes encoding proteins, the function of which in peripheral nerve maintenance is notyet clear. Despite the increase in the number of known genes, especially for CMT2, there are many patients in whom no mutation can yet be found.
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PMID:[From gene to disease; Charcot-Marie-Tooth disease or the hereditary motor and sensory neuropathies]. 1603 95

The objective of this study was to report a novel exon-1 mutation in the myelin protein zero (MPZ) gene, resulting in axonal Charcot-Marie-Tooth neuropathy with recurrent hyper-CK-emia. In a 64-year-old woman slowly progressive distal lower limb weakness, muscle cramps in the lower limb muscles, and stocking-type numbness had developed from the age of 61. Neurologic examination revealed discrete hip flexor weakness, weakness for foot extension, diffuse wasting of the distal lower limb muscles, reduced patella tendon reflexes, and absent Achilles tendon reflexes. There was recurrently elevated creatine kinase with a maximum of 607 U/l (n, <145 U/l). Stimulation of the peroneal and tibial nerves did not evoke a muscular response. Electromyography was neurogenic. Biopsy of the right sural nerve showed diffuse axonal degeneration and loss of axons of all diameters. Muscle biopsy showed increased fiber-size variability, angulated fibers, internalized nuclei, accumulations of nuclei, grouped atrophic muscle fibers, and fiber splitting. Molecular genetic analysis by PCR and direct nucleotide sequencing revealed the heterozygous C59T exon-1 MPZ gene mutation, resulting in the amino acid exchange S20F of the MPZ signal protein domain (leader peptide). The novel C59T mutation in the leader peptide of the MPZ gene is pathogenic and manifests as severe, late-onset, axonal, symmetric sensorimotor polyneuropathy (CMT2) and hyper-CK-emia.
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PMID:Novel C59T leader peptide mutation in the MPZ gene associated with late-onset, axonal, sensorimotor polyneuropathy. 1698 71

Inherited peripheral neuropathies belong to the most common neuromuscular disorders and occur worldwide (1/2500). The best known is Charcot Marie Tooth (CMT), an inherited disorder first described in 1886. Most patients have progressive weakness and wasting of foot and hand muscles. Treatment is currently supportive (braces and foot surgery) and a therapy that fundamentally alters the course of these diseases is still lacking. The involvement of a specific subset of neurons is a key hallmark in the disease process. One subgroup, distal hereditary motor neuropathy (distal HMN) is characterized by the selective loss of motor neurons and/or their long axons in the peripheral nervous system. Apart from the absence of sensory abnormalities, distal HMN closely resembles axonal CMT2. A better understanding of the molecular architecture of the peripheral nerve, the functional pathways, the myelination process and the complex interaction between the axon, the myelinating Schwann cells and muscle is crucial to identify targets for therapeutic interventions. Identification of loci, genes and disease-causing mutations is the first step in this understanding and opens new perspectives for molecular genetic diagnosis. Genotype-phenotype correlations guide the selection of specific mutations suitable for functional analysis in cellular and animal models. The knowledge gained from the molecular genetic and biological research will also help to make progress in the study of acquired peripheral neuropathies. Some of these neuropathies are often therapy-resistant, have a profound influence on the quality of life of the patients, and constitute a financial burden for both the individual and the community.
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PMID:A molecular genetic update of inherited distal motor neuropathies. 1851 57

Mutations in the gene encoding 27-kDa small heat-shock protein B1 (HSPB1) have been reported in association with Charcot-Marie-Tooth disease type 2F or dHMN type II. We describe an Italian patient with wasting and weakness of distal muscles, involving primarily and mostly the lower limbs and later the upper limbs, in which a novel mutation of HSPB1, T180I, was detected. Electrophysiological evaluation disclosed a pure motor axonal neuropathy. Sural nerve biopsy showed a mild reduction of myelinated fibre density. All these findings suggested a CMT2/dHMN phenotype.
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PMID:A novel HSPB1 mutation in an Italian patient with CMT2/dHMN phenotype. 2087 Feb 50

Some of the metabolic disorders are manifested by a predominantly expressed symptoms from the single organ, however, they display discrete symptoms from other tissues. Charcot Marie Tooth disease (CMT) divided into demyelinating (CMT1) and axonal (CMT2) subtypes is characterized by a slowly progressive wasting of distal muscles. CMT2A form diagnosis requires identification of mutation in a gene coding for mitofusin 2 (MFN2). Mitofusin 2 is a protein of an outer mitochondrial membrane encoded in the nuclear genome and characterized by numerous biochemical functions. Mfn2 is involved mainly in the fusion of mitochondria and the cooperation between endoplasmic reticulum and mitochondria. It seems probably that Mfn2 possesses also some regulatory functions and takes part in a regulation of respiratory chain activity, transcription of several proteins and in intracellular signals transduction. Mfn2-linked pathology is also observed in diabetes and heart diseases. Here, we aim to show that mitofusin 2 is a protein crucial not only for peripheral nerve disorders but is a one of the common regulator of cell metabolism.
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PMID:[Mitofusin 2 as a crucial peripheral nervous system protein and a common regulator of cell metabolism]. 2191 23

Mitofusin 2 (MFN2) mutations are the most common cause of axonal Charcot-Marie-Tooth disease (CMT2). The majority are inherited in an autosomal dominant manner but recessive and semi-dominant kindreds have also been described. We previously reported a deletion of exons 7 and 8 resulting in nonsense-mediated decay, segregating with disease when present in trans with another pathogenic MFN2 mutation. Detailed clinical and electrophysiological data on a series of five affected patients from four kindreds and, when available, their parents and relatives were collected. MFN2 Sanger sequencing, multiplex ligation probe amplification, and haplotype analysis were performed. A severe early-onset CMT phenotype was seen in all cases: progressive distal weakness, wasting, and sensory loss from infancy or early childhood. Optic atrophy (four of five) and wheelchair dependency in childhood were common (four of five). All were compound heterozygous for a deletion of exons 7 and 8 in MFN2 with another previously reported pathogenic mutation (Phe216Ser, Thr362Met, and Arg707Trp). Carrier parents and relatives were unaffected (age range: 24-82 years). Haplotype analysis confirmed that the deletion had a common founder in all families.
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PMID:MFN2 deletion of exons 7 and 8: founder mutation in the UK population. 2611 2

Charcot-Marie-Tooth (CMT) disease, also referred to as hereditary motor and sensory neuropathy (HMSN), is a heterogeneous group of disorders which primarily affects the peripheral nervous system. Clinically, the main features are progressive muscle weakness seen distally, along with wasting seen predominantly in the anterior compartments of the lower legs. The disease can broadly be classified into two groups, CMT1 and CMT2-based on inheritance patterns, paired with anatomical or electrophysiological findings. It can be inherited in the autosomal dominant, X-linked and rarely, the autosomal recessive fashions. Here, we present an unusual case of autosomal recessive CMT disease, in four out of six children of unaffected parents in a family.
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PMID:Affected Children of Healthy Parents: Multiple Pediatric Cases of Autosomal Recessive Charcot-Marie-Tooth Disease in a Pakistani Family. 3124 5

Mutations in TRPV4 are linked to a group of clinically distinct, but also overlapping axonal neuropathies, including Charcot-Marie-Tooth disease type 2C (CMT2C), scapuloperoneal spinal muscular atrophy, and congenital distal spinal muscular atrophy. The incidence of TRPV4-linked cases ranges from 0 to 7% in overall axonal neuropathy cohorts from European countries and Australia. However, the data from other areas remain largely unknown. In this study, we screened for TRPV4 mutations in a well-characterized USA cohort of 62 unrelated CMT2 patients without mutations in MFN2, GARS, NEFL, and GDAP1. All 15 coding exons of TRPV4 were analyzed by Sanger-sequencing. Clinical features of TRPV4-linked patients were compared with those lacking TRPV4 mutations. We identified two TRPV4 mutations in two patients. A TRPV4-R316C was identified in a patient with family history, while a TRPV4-R269C in an apparently sporadic case. Marked clinical variations were observed in the patients with TRPV4 mutations. Our data suggest that TRPV4-linked CMT2C accounts for a sizable fraction in this USA cohort of CMT2; it has a wide phenotypic spectrum, and vocal cord paralysis, scapular weakness and wasting, skeletal dysplasia, and hearing loss are suggestive signs for TRPV4-linked CMT2C.
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PMID:Incidence and Clinical Features of TRPV4-Linked Axonal Neuropathies in a USA Cohort of Charcot-Marie-Tooth Disease Type 2. 3146 27


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