Charcot-Marie-Tooth Disease and Related Genetic Neuropathies
The inherited peripheral neuropathies are a complex group of disorders caused by mutations in more than 50 genes. Scientifically, these disorders provide extensive information on molecular pathways that cause demyelination, axonal loss, and abnormal interactions between Schwann cells and the axons they ensheathe. Clinically, however, these neuropathies are confusing because it is difficult to determine what gene to test for in a given patient, inheritance patterns may differ among patients, and genetic testing is expensive. This review provides a biological context and guidelines to help neurologists better understand the basis and focus of genetic testing for these disorders.
In the past 5 years, many of the genetic causes of inherited neuropathies have been discovered and the phenotypes of inherited neuropathies have been characterized. Clinical trials of genetic neuropathies are now underway.
It is hoped that this review will lead to a better understanding of these fascinating neuropathies for health care professionals and that this improved understanding will facilitate treatment advances for these presently untreatable diseases.
Available from: Oranee Sanmaneechai
- "However, Tyr119Cys allows myelination to develop and causes an adult onset neuropathy. Moreover, while Arg98Cys causes infantile disease it appears to do so by activating an intracellular process called the unfolded protein response rather than by disrupting myelin wrapping (Patzko et al., 2012; Saporta et al., 2012). Therefore, how a novel cysteine would cause neuropathy in CMT1B is more complicated than initially perceived. "
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ABSTRACT: We aimed to characterize genotype-phenotype correlations and establish baseline clinical data for peripheral neuropathies caused by mutations in the myelin protein zero (MPZ) gene. MPZ mutations are the second leading cause of Charcot-Marie-Tooth disease type 1. Recent research makes clinical trials for patients with MPZ mutations a realistic possibility. However, the clinical severity varies with different mutations and natural history data on progression is sparse. We present cross-sectional data to begin to define the phenotypic spectrum and clinical baseline of patients with these mutations. A cohort of patients with MPZ gene mutations was identified in 13 centres of the Inherited Neuropathies Consortium - Rare Disease Clinical Research Consortium (INC-RDCRC) between 2009 and 2012 and at Wayne State University between 1996 and 2009. Patient phenotypes were quantified by the Charcot-Marie-Tooth disease neuropathy score version 1 or 2 and the Charcot-Marie-Tooth disease paediatric scale outcome instruments. Genetic testing was performed in all patients and/or in first- or second-degree relatives to document mutation in MPZ gene indicating diagnosis of Charcot-Marie-Tooth disease type 1B. There were 103 patients from 71 families with 47 different MPZ mutations with a mean age of 40 years (range 3-84 years). Patients and mutations were separated into infantile, childhood and adult-onset groups. The infantile onset group had higher Charcot-Marie-Tooth disease neuropathy score version 1 or 2 and slower nerve conductions than the other groups, and severity increased with age. Twenty-three patients had no family history of Charcot-Marie-Tooth disease. Sixty-one patients wore foot/ankle orthoses, 19 required walking assistance or support, and 10 required wheelchairs. There was hearing loss in 21 and scoliosis in 17. Forty-two patients did not begin walking until after 15 months of age. Half of the infantile onset patients then required ambulation aids or wheelchairs for ambulation. Our results demonstrate that virtually all MPZ mutations are associated with specific phenotypes. Early onset (infantile and childhood) phenotypes likely represent developmentally impaired myelination, whereas the adult-onset phenotype reflects axonal degeneration without antecedent demyelination. Data from this cohort of patients will provide the baseline data necessary for clinical trials of patients with Charcot-Marie-Tooth disease caused by MPZ gene mutations.
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Available from: Wilson Marques
- "Interestingly, some of these patients exhibit intellectual deficits (Genari et al., 2011). The typical CMT phenotype includes onset of predominantly motor length-dependent sensory and motor polyneuropathies within the first two decades of life associated with variable sensory manifestations, decreased or absent tendon jerks, and skeletal abnormalities, such as pes cavus, hammer toes, and scoliosis (Thomas et al., 1997; Marques et al., 2005; Patzko and Shy, 2012) However, marked clinical heterogeneity exists, even for the same mutation, in the same family and for identical twins (Marques et al., 1999). Genetic and non-genetic factors must therefore be involved. "
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ABSTRACT: This study aimed to conduct a systematic literature review regarding the associations between psychiatric symptoms, functional impairments, and quality of life in patients with CMT. The PUBMED, PsycInfo, SCIELO, and LILACS electronic databases were used, and the following search terms were employed: Charcot-Marie-Tooth, hereditary motor and sensory neuropathy (HMSN), mental disorder, quality of life, psychiatry, psychiatric, and psychological without the use of time-limit filters. According to the adopted inclusion criteria, 20 studies were included and appraised. These studies indicated that patients with CMT exhibited an increased trend toward depressive symptoms compared with the general population. In addition, CMT patients were exposed to a higher risk of reduced quality of life and significant sleep impairment. Considering the comorbidity of CMT with other psychiatric disorders, the heterogeneity of the instruments used to evaluate the psychiatric symptoms compromised the ability to compare the studies examined. Our results indicate a need for a systematic evaluation of these conditions to minimise the impairments and decreased quality of life caused by CMT.
Available from: Leah Reznikov
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ABSTRACT: Peripheral nervous system abnormalities, including neuropathy, have been reported in people with cystic fibrosis. These abnormalities have largely been attributed to secondary manifestations of the disease. We tested the hypothesis that disruption of the cystic fibrosis transmembrane conductance regulator (CFTR) gene directly influences nervous system function by studying newborn CFTR(-/-) pigs. We discovered CFTR expression and activity in Schwann cells, and loss of CFTR caused ultrastructural myelin sheath abnormalities similar to those in known neuropathies. Consistent with neuropathic changes, we found increased transcripts for myelin protein zero, a gene that, when mutated, can cause axonal and/or demyelinating neuropathy. In addition, axon density was reduced and conduction velocities of the trigeminal and sciatic nerves were decreased. Moreover, in vivo auditory brainstem evoked potentials revealed delayed conduction of the vestibulocochlear nerve. Our data suggest that loss of CFTR directly alters Schwann cell function and that some nervous system defects in people with cystic fibrosis are likely primary.
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