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EN
Knowledge whether a certain DNA variant is a pathogenic mutation or a harmless polymorphism is a critical issue in medical genetics, in which results of a molecular analysis may serve as a basis for diagnosis and genetic counseling. Due to its genetic heterogeneity expressed at the levels of loci, genes and mutations, Charcot-Marie-Tooth (CMT) disease can serve as a model group of clinically homogenous diseases for studying the pathogenicity of mutations. Close to a 17p11.2-p12 duplication occurring in 70% of patients with the demyelinating form of CMT disease, numerous mutations have been identified in poorly characterized genes coding for proteins of an unknown function. Functional analyses, segregation analyses of large pedigrees, and inclusion of large control groups are required to assess the potential pathogenicity of CMT mutations. Hence, the pathogenicity of numerous CMT mutations remains unclear. Some variants detected in the CMT genes and originally described as pathogenic mutations have been shown to have a polymorphic character. In contrast, polymorphisms initially considered harmless were later reclassified as pathogenic mutations. However, the process of assessing the pathogenicity of mutations, as presented in this study for CMT disorders, is a more general issue concerning all disorders with a genetic background. Since the number of DNA variants is still growing, in the near future geneticists will increasingly have to cope with the problem of pathogenicity of identified genetic variants.
EN
Charcot-Marie-Tooth type X1 disease (CMTX1) is an X-dominant peripheral neuropathy caused by mutations in the GJB1 gene. Molecular genetic analysis of the GJB1 gene is crucial for CMTX1 diagnosis and for genetic counselling. To date, molecular genetic analysis of the GJB1 gene revealed 264 mutations in the GJB1 gene. In spite of the rising number of GJB1 gene mutations, family history was documented in only a few CMTX1 cases. The aim of this study was a molecular genetic analysis of the GJB1 gene in 7 families, performed in 19 CMTX1-affected patients and 13 healthy family members. Moreover, we attempted to report evidence of effects of 6 amino-acid substitutions described in this study. To the best of our knowledge, the G110D, V152D and K167E mutations are novel substitutions, which have not been reported so far.
EN
Among 57 mutations in the peripheral myelin protein 22 gene (PMP22) identified so far in patients affected by Charcot-Marie-Tooth disease (CMT), only 8 have been shown to segregate with a mixed phenotype of CMT and hearing impairment. In this study, we report a new Ser112Arg mutation in the PMP22 gene, identified in a patient with early-onset CMT and slowly progressive hearing impairment beginning in the second decade of life. We suggest that the Ser112Arg mutation in the PMP22 gene might have a causative role in the early-onset CMT with hearing impairment. Thus, our study extends the spectrum of CMT phenotypes putatively associated with PMP22 gene mutations
EN
Within the last decade, numerous methods have been applied to detect the most common mutation in patients affected with Charcot-Marie-Tooth (CMT) disease, i.e. submicroscopic duplication in the 17p11.2-p12 region. In 1993, another neuropathy ? known as hereditary neuropathy with liability to pressure palsies (HNPP) -has been shown to be caused by a 17p11.2-p12 deletion. Historically, Southern blot analysis was the first approach to identify CMT1A duplication or HNPP deletion. This time- and labor-consuming method requires prior selection of DNA samples. In fact, only CMT patients affected with the demyelinating form of CMT1 have been screened for CMT1A duplication. After the 17p11.2-p12 duplication was identified in the CMT1 families, subsequent studies revealed additional axonal features in the patients harboring the 17p11.2-p12 duplication. Thus it seems reasonable to test all patients affected with CMT for the presence of the 17p11.2-p12 duplication. To evaluate the utility of real-time polymerase chain reaction (Q-PCR) and restriction fragment length polymorphism PCR (RFLP-PCR), we screened a large group of 179 families with the diagnosis of CMT/HNPP for the presence of the 17p11.2-p12 duplication/deletion. Due to a high frequency of CMT1A duplication in familial cases of CMT, we propose (in contrast to the previous studies) to perform Q-PCR analysis in all patients diagnosed with CMT.
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