Alternative splicing may contribute to time-dependent manifestation of inherited erythromelalgia.

The Na(v)1.7 sodium channel is preferentially expressed in nocioceptive dorsal root ganglion and sympathetic ganglion neurons. Gain-of-function mutations in Na(v)1.7 produce the nocioceptor hyperexcitability underlying inherited erythromelalgia, characterized in most kindreds by early-age onset of severe pain. Here we describe a mutation (Na(v)1.7-G616R) in a pedigree with adult-onset of pain in some family members. The mutation shifts the voltage-dependence of channel fast-inactivation in a depolarizing direction in the adult-long, but not in the neonatal-short splicing isoform of Na(v)1.7 in dorsal root ganglion neurons. Altered inactivation does not depend on the age of the dorsal root ganglion neurons in which the mutant is expressed. Expression of the mutant adult-long, but not the mutant neonatal-short, isoform of Na(v)1.7 renders dorsal root ganglion neurons hyperexcitable, reducing the current threshold for generation of action potentials, increasing spontaneous activity and increasing the frequency of firing in response to graded suprathreshold stimuli. This study shows that a change in relative expression of splice isoforms can contribute to time-dependent manifestation of the functional phenotype of a sodium channelopathy.

Identification of the variant Ala335Val of MED25 as responsible for CMT2B2: molecular data, functional studies of the SH3 recognition motif and correlation between wild-type MED25 and PMP22 RNA levels in CMT1A animal models.

Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous disorder. All mendelian patterns of inheritance have been described. We identified a homozygous p.A335V mutation in the MED25 gene in an extended Costa Rican family with autosomal recessively inherited Charcot-Marie-Tooth neuropathy linked to the CMT2B2 locus in chromosome 19q13.3. MED25, also known as ARC92 and ACID1, is a subunit of the human activator-recruited cofactor (ARC), a family of large transcriptional coactivator complexes related to the yeast Mediator. MED25 was identified by virtue of functional association with the activator domains of multiple cellular and viral transcriptional activators. Its exact physiological function in transcriptional regulation remains obscure. The CMT2B2-associated missense amino acid substitution p.A335V is located in a proline-rich region with high affinity for SH3 domains of the Abelson type. The mutation causes a decrease in binding specificity leading to the recognition of a broader range of SH3 domain proteins. Furthermore, Med25 is coordinately expressed with Pmp22 gene dosage and expression in transgenic mice and rats. These results suggest a potential role of this protein in the molecular etiology of CMT2B2 and suggest a potential, more general role of MED25 in gene dosage sensitive peripheral neuropathy pathogenesis.

Mutations in the LMNA gene do not cause axonal CMT in Czech patients.

The LMNA gene was sequenced in 98 Czech patients from 94 unrelated families with early-onset axonal Charcot-Marie-Tooth (CMT) disease consistent with both autosomal recessive inheritance and sporadic cases. Biallelic pathogenic mutations were not found in any patient in this group. One patient carried the c.1870C>T mutation that is predicted to result in the amino-acid substitution, p. Arg624Cys, on one allele, but the second causative mutation was not detected. LMNA mutation is not likely to be associated with the disease in this family. To exclude larger deletions/duplications in the LMNA gene not detectable by sequencing, 48 patients from this group were also analyzed with multiplex ligation-dependent probe amplification. No rearrangements in the LMNA gene were detected. We conclude that mutations in the LMNA gene are absent from a large group of Czech patients with axonal autosomal recessive CMT disease. Consequently, LMNA mutation screening does not seem to be relevant for axonal CMT DNA diagnostics. A similar situation may apply to other European populations.

Novel missense, insertion and deletion mutations in the neurotrophic tyrosine kinase receptor type 1 gene (NTRK1) associated with congenital insensitivity to pain with anhidrosis.

Hereditary sensory and autonomic neuropathy type IV (HSAN IV) or congenital insensitivity to pain with anhidrosis (CIPA) is an autosomal-recessive disorder affecting the neurotrophin signal transduction pathway. HSAN IV is characterized by absence of reaction to noxious stimuli, recurrent episodes of fever, anhidrosis, self mutilating behaviour and frequent mental retardation. Mutations in the neurotrophic tyrosine kinase receptor type 1 (NTRK1) are associated with this disorder. We investigated NTRK1 mutations in five HSAN IV patients and one less typical patient with hypohidrosis, insensitivity to pain as well as motor- and sensory deficits in the peripheral nervous system. For the HSAN IV patients we identified a homozygous missense mutation (p.I572S), a homozygous deletion of 1985bp (g.7335164-7336545del), a homozygous insertion c.722_723insC in exon 7 and two compound heterozygous mutations (p.Q558X+p.L717R). The less typical patient as well as one HSAN IV patient revealed no NTRK1 mutation.

Clinical, pathological and molecular findings in two siblings with giant axonal neuropathy (GAN): report from India.

BACKGROUND: Giant axonal neuropathy (GAN, MIM: 256850) is characterized by an early onset of severe peripheral neuropathy, varying central nervous system involvement and strikingly frizzly hair. Mode of inheritance is autosomal recessive. Mutations in the gigaxonin (GAN) gene on chromosome 16q24.1 are frequently observed for this disorder, but genetic heterogeneity has been demonstrated for a milder variant of GAN. Gigaxonin binds C-terminally to various microtubule associated proteins causing their ubiquitin-mediated degradation. For several gigaxonin mutations it was shown that they hamper this process resulting finally in accumulation of microtubule associated proteins which may disturb cellular functions. Here, we report a family originating in India with two patients showing typical clinical signs suggestive of GAN. METHODOLOGY: Genomic DNA was analyzed for both siblings and their parents in order to detect the molecular changes in the GAN gene. The complete coding region including flanking sequences was amplified using published primer sequences. The PCR products were sequenced on both strands after purification using an ABI 3730 (Applied Biosystems) capillary sequencer. The resulting sequences were evaluated using SeqPilot (JSI-medical systems GmbH) and were compared to the reference sequences (NT_024797, NM_022041) given in the NCBI-database. CONCLUSIONS: An AluYa5 insertion (c.1657ALUYa5ins, p.Thr553_Pro597del) in exon 11 of the GAN gene was identified homozygous in both siblings, whereas the parents were heterozygous carriers of this mutation. Here, the reported mutation is located in C-terminal part of the protein affecting the terminal kelch domain. Thus a functional important part of the protein is altered by the AluYa5 insertion and causes GAN.

Cerebral involvement in axonal Charcot-Marie-Tooth neuropathy caused by mitofusin2 mutations.

Mutations in the mitofusin 2 (MFN2) gene are a major cause of primary axonal Charcot- Marie-Tooth (CMT) neuropathy. This study aims at further characterization of cerebral white matter alterations observed in patients with MFN2 mutations. Molecular genetic, magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and diffusion tensor imaging (DTI) investigations were performed in four unrelated patients aged 7 to 38 years with early onset axonal CMT neuropathy. Three distinct and so far undescribed MFN2 mutations were detected. Two patients had secondary macrocephaly and mild diffuse predominantly periventricular white matter alterations on MRI. In addition, one boy had symmetrical T2-hyperintensities in both thalami. Two patients had optic atrophy, one of them with normal MRI. In three patients proton MRS revealed elevated concentrations of total N-acetyl compounds (neuronal marker), total creatine (found in all cells) and myo-inositol (astrocytic marker) in cerebral white and gray matter though with regional variation. These alterations were most pronounced in the two patients with abnormal MRI. DTI of these patients revealed mild reductions of fractional anisotropy and mild increase of mean diffusivity in white matter. The present findings indicate an enhanced cellular density in cerebral white matter of MFN2 neuropathy which is primarily due to a reactive gliosis without axonal damage and possibly accompanied by mild demyelination.

Novel mutations in the Charcot-Marie-Tooth disease genes PMP22, MPZ, and GJB1.

Charcot-Marie-Tooth disease (CMT) is a clinically and genetically heterogeneous disorder of the peripheral nervous system. CMT type 1 is most frequently caused by a 1.4 Mb tandem duplication in chromosome 17p11.2 comprising the peripheral myelin protein 22 (PMP22) gene. Furthermore sequence variations of PMP22, myelin protein zero (MPZ) and the gap junction protein b 1 gene (GJB1 or Connexin 32) may cause a variety of distinct CMT phenotypes. In this study we screened DNA from 42 unrelated patients for mutations in the PMP22, MPZ and GJB1 genes. Four novel mutations were identified. A Val65Phe amino acid exchange in PMP22 causes CMT type 1 associated with deafness, in GJB1 Tyr7_Thr8delinsSer, Pro172Ala and Ser138Asn are causes of CMTX neuropathies".

A novel myosin heavy chain gene in human chromosome 19q13.3.

A human myosin heavy chain gene was identified in chromosome 19q13 by computational sequence analysis, RT-PCR and DNA sequencing of the cDNA. The complete cDNA has a length of 6786 bp and comprises 41 exons (40 coding) included in 108 kb of genomic sequence. Alternative splicing variants were also identified. The gene is expressed in a multitude of tissues, but mainly in small intestine, colon and skeletal muscle. The putative protein (228 kDa) carries the common myosin domains and presents high homology with the non-muscle myosin heavy chains (MYH9 and MYH10) as well as the smooth muscle myosin heavy chain MYH11. Nevertheless, phylogenetic analysis indicated that these homologous proteins are more related among themselves than to MYH14, suggesting that possibly this myosin heavy chain should be classified in a new myosin-subfamily.