Linkage analyses and characterization of candidate gene locuses and genes in families with multiple appearance of hereditary neuropathy Charcot-Marie-Tooth or deafness with unexplained gene defect

Topics of the Ph.D. studies were: 1) hereditary neuropathy and 2) non-syndromic hearing loss Ad 1) The larger part of the dissertation thesis is devoted to hereditary neuropathies Charcot-Marie-Tooth (CMT). Four families with hereditary neuropathy were examined by the linkage analysis on SNP chips. The other part describe the analysis of new mutations in the GJB1, MPZ and PMP22 genes. Ad 2) The author performed the homozygosity mapping in a Czech Roma families with non-syndromic hearing loss

Linkage analyses and characterization of candidate gene locuses and genes in families with multiple appearance of hereditary neuropathy Charcot-Marie-Tooth or deafness with unexplained gene defect

Topics of the Ph.D. studies were: 1) hereditary neuropathy and 2) non-syndromic hearing loss Ad 1) The larger part of the dissertation thesis is devoted to hereditary neuropathies Charcot-Marie-Tooth (CMT). Four families with hereditary neuropathy were examined by the linkage analysis on SNP chips. The other part describe the analysis of new mutations in the GJB1, MPZ and PMP22 genes. Ad 2) The author performed the homozygosity mapping in a Czech Roma families with non-syndromic hearing loss

MARVELD2 (DFNB49) mutations in the hearing impaired Central European Roma population--prevalence, clinical impact and the common origin.

In the present study we aimed: 1) To establish the prevalence and clinical impact of DFNB49 mutations in deaf Roma from 2 Central European countries (Slovakia and Hungary), and 2) to analyze a possible common origin of the c.1331+2T>C mutation among Roma and Pakistani mutation carriers identified in the present and previous studies.We sequenced 6 exons of the MARVELD2 gene in a group of 143 unrelated hearing impaired Slovak Roma patients. Simultaneously, we used RFLP to detect the c.1331+2T>C mutation in 85 Hungarian deaf Roma patients, control groups of 702 normal hearing Romanies from both countries and 375 hearing impaired Slovak Caucasians. We analyzed the haplotype using 21 SNPs spanning a 5.34Mb around the mutation c.1331+2T>C.One pathogenic mutation (c.1331+2T>C) was identified in 12 homozygous hearing impaired Roma patients. Allele frequency of this mutation was higher in Hungarian (10%) than in Slovak (3.85%) Roma patients. The identified common haplotype in Roma patients was defined by 18 SNP markers (3.89 Mb). Fourteen common SNPs were also shared among Pakistani and Roma homozygotes. Biallelic mutation carriers suffered from prelingual bilateral moderate to profound sensorineural hearing loss.We demonstrate different frequencies of the c.1331+2T>C mutation in hearing impaired Romanies from 3 Central European countries. In addition, our results provide support for the hypothesis of a possible common ancestor of the Slovak, Hungarian and Czech Roma as well as Pakistani deaf patients. Testing for the c.1331+2T>C mutation may be recommended in GJB2 negative Roma cases with early-onset sensorineural hearing loss

Cosegregation of haplotypes in a Slovak Roma family (SK5) with DFNB49 related deafness caused by the c.1331+2T>C mutation.

<p>The filled symbol represents the proband with hearing impairment; symbols with dot represent normal hearing carriers. Alleles forming the risk haplotype are shown in grey boxes.</p

Common ancestral haplotypes of Slovak, Hungarian and Czech Romanies, and Pakistani patients.

<p>The haplotypes in Slovak (SK), Czech (CZ), Hungarian (HU) Roma and Pakistani patients with the c.1331+2T>C mutation, and haplotypes in Slovak Roma controls without the c.1331+2T>C mutation. The c.1331+2T>C mutation is shown in bold. The common haplotype is highlighted in light grey.^aThe most similar haplotypes found in 5 out of 56 control individuals. In the remaining 51 control individuals, haplotypes were significantly distinguishable.^bThe haplotype in Pakistani patients with c.1183-1G>A mutation.</p

Mutations in ATP1A1 Cause Dominant Charcot-Marie-Tooth Type 2

Although mutations in more than 90 genes are known to cause CMT, the underlying genetic cause of CMT remains unknown in more than 50% of affected individuals. The discovery of additional genes that harbor CMT2-causing mutations increasingly depends on sharing sequence data on a global level. In this way—by combining data from seven countries on four continents—we were able to define mutations in ATP1A1, which encodes the alpha1 subunit of the Na+,K+-ATPase, as a cause of autosomal-dominant CMT2. Seven missense changes were identified that segregated within individual pedigrees: c.143T>G (p.Leu48Arg), c.1775T>C (p.Ile592Thr), c.1789G>A (p.Ala597Thr), c.1801_1802delinsTT (p.Asp601Phe), c.1798C>G (p.Pro600Ala), c.1798C>A (p.Pro600Thr), and c.2432A>C (p.Asp811Ala). Immunostaining peripheral nerve axons localized ATP1A1 to the axolemma of myelinated sensory and motor axons and to Schmidt-Lanterman incisures of myelin sheaths. Two-electrode voltage clamp measurements on Xenopus oocytes demonstrated significant reduction in Na+ current activity in some, but not all, ouabain-insensitive ATP1A1 mutants, suggesting a loss-of-function defect of the Na+,K+ pump. Five mutants fall into a remarkably narrow motif within the helical linker region that couples the nucleotide-binding and phosphorylation domains. These findings identify a CMT pathway and a potential target for therapy development in degenerative diseases of peripheral nerve axons