Paschalis Nicolaou

Down-regulation of myogenin can reverse terminal muscle cell differentiation.

Certain higher vertebrates developed the ability to reverse muscle cell differentiation (dedifferentiation) as an additional mechanism to regenerate muscle. Mammals, on the other hand, show limited ability to reverse muscle cell differentiation. Myogenic Regulatory Factors (MRFs), MyoD, myogenin, Myf5 and Myf6 are basic-helix-loop-helix (bHLH) transcription factors essential towards the regulation of myogenesis. Our current interest is to investigate whether down-regulation of MRFs in terminally differentiated mouse myotubes can induce reversal of muscle cell differentiation. Results from this work showed that reduction of myogenin levels in terminally differentiated mouse myotubes can reverse their differentiation state. Down-regulation of myogenin in terminally differentiated mouse myotubes induces cellular cleavage into mononucleated cells and cell cycle re-entry, as shown by re-initiation of DNA synthesis and increased cyclin D1 and cyclin E2 levels. Finally, we provide evidence that down-regulation of myogenin causes cell cycle re-entry (via down-regulation of MyoD) and cellularisation through separate pathways. These data reveal the important role of myogenin in maintaining terminal muscle cell differentiation and point to a novel mechanism by which muscle cells could be re-activated through its down-regulation.

Phenotypic and cellular expression of two novel connexin32 mutations causing CMT1X

Objective: To determine the phenotypic and cellular expression of two novel connexin32 (Cx32) mutations causing X-linked Charcot–Marie–Tooth disease (CMT1X). Methods: The authors evaluated several members of two families with CMT1X clinically, electrophysiologically, pathologically, and by genetic testing. The Cx32 mutations were expressed in vitro and studied by immunocytochemistry. Results: In both families, men were more severely affected than women with onset in the second decade of life. In the first family, the phenotype was that of demyelinating polyneuropathy with variable involvement of peripheral nerves. There was clinical evidence of CNS involvement in at least three of the patients, with extensor plantar responses and brisk reflexes. In the second family, the affected man presented with symmetric polyneuropathy and intermediate slowing of conduction velocities, whereas affected women had prominent asymmetric atrophy of the leg muscles. The authors identified two novel missense mutations resulting in L143P amino acid substitution in the first family and in V140E substitution in the second family, both located in the third transmembrane domain of Cx32. Expression of these Cx32 mutations in communication-incompetent HeLa cells and immunocytochemical analysis revealed that both mutants were retained intracellularly and were localized in the Golgi apparatus. In contrast to wild-type protein, they did not form gap junctions. Conclusion: These novel connexin32 (Cx32) mutations cause a spectrum of clinical manifestations characteristic of Charcot–Marie–Tooth disease (CMT1X), including demyelinating or intermediate polyneuropathy, which is often asymmetric, and CNS involvement in one family. The position and cellular expression of Cx32 mutations alone cannot fully predict these phenotypic variations in CMT1X.

Charcot-Marie-Tooth Disease in Cyprus: Epidemiological, Clinical and Genetic Characteristics

Background: Charcot-Marie-Tooth disease (CMT) is the most common inherited neuropathy. CMT is classified into 2 main subgroups: a demyelinating and an axonal type. Further subdivisions within these 2 main categories exist and intermediate forms have more recently been described. Inheritance can be autosomal dominant, recessive or X-linked. CMT is associated with more than 30 loci, and about 25 causative genes have been described thus far. Methods: We studied epidemiological, clinical and genetic characteristics of CMT in the Cypriot population. Results: The prevalence of CMT in Cyprus on January 15, 2009, is estimated to be 16 per 100,000. Thirty-three families and 8 sporadic patients were ascertained. CMT was demyelinating in 52%, axonal in 33% and intermediate in 15% of the patients. Thirteen families had PMP22 duplication, 3 families had the PMP22 S22F mutation, 4 families had GJB1/Cx32 mutations, 2 families had different MPZ mutations, 1 of them novel, and 2 families had different MFN2 mutations. Nine families and 8 sporadic patients were excluded from the common CMT genes. Conclusion: The most frequent CMT mutation worldwide, the PMP22 duplication, is also the most frequent CMT mutation in the Cypriot population. Five out of the 8 other mutations are novel, not reported in other populations.

A novel PMP22 mutation Ser22Phe in a family with hereditary neuropathy with liability to pressure palsies and CMT1A phenotypes

Abstract.We describe a Cypriot family in which some family members presented with episodes of pressure palsies, while other family members had a slowly progressive chronic polyneuropathy typical of the Charcot-Marie-Tooth type 1 phenotype. All family members were evaluated clinically, with nerve conduction studies, and with genetic testing. In all affected individuals there was clinical and electrophysiological evidence of diffuse demyelinating sensorimotor polyneuropathy and a novel point mutation in the PMP22 gene (Ser22Phe) was identified.

A novel LRSAM1 mutation is associated with autosomal dominant axonal Charcot-Marie-Tooth disease

Charcot-Marie-Tooth (CMT) disease is the most common hereditary neuropathy resulting from mutations in >30 genes expressed in either the Schwann cells or the axon of peripheral nerves. The disease is classified into demyelinating (CMT1), axonal (CMT2) or intermediate (CMTI) based on electrophysiological and pathological findings. Our study focused on the identification of a novel disease mutation in a large Sardinian family with CMT2 of autosomal dominant (AD) inheritance. All available family members were clinically evaluated and samples were collected from consenting individuals. Initially, we excluded known CMT2 genes/loci in this family. We then conducted a genome-wide linkage analysis and mapped the gene to chromosome 9q33–q34. Refined linkage and haplotype analyses defined an 11.6-Mb candidate region with a maximum LOD score of 8.06. Following exclusion of several candidate genes from the region, we targeted the LRSAM1 (leucine-rich repeat and sterile alpha motif-containing 1) gene, very recently found to be associated with autosomal recessive CMT2 in one family. For a more efficient investigation of this large gene, already available proband RNA (cDNA) was initially analyzed. Targeted DNA analysis then confirmed a novel LRSAM1 splice-site (c.2047-1G>A) mutation, causing a frameshift that introduces a stop codon three amino acids further down the new reading frame (p.Ala683ProfsX3). This mutation is located in the C-terminal RING finger motif of the encoded protein and leads to premature truncation of the protein. In the course of our work, a second LRSAM1 mutation dominantly transmitted was identified by another group. Our data further confirms that LRSAM1 mutations are associated with CMT2 of AD inheritance.

A novel GDAP1 mutation 439delA is associated with autosomal recessive CMT disease.

BACKGROUND Charcot-Marie-Tooth (CMT) disease is the most common form of inherited motor and sensory neuropathy. Based on neurophysiological and neuropathological criteria CMT has been sub-classified into two main types: demyelinating and axonal. Furthermore, it is genetically heterogeneous with autosomal dominant, autosomal recessive (AR) and X-linked modes of inheritance. Thus far, seven genes have been identified in association with the demyelinating AR-CMT disease. We hereby report our clinical and molecular genetic findings in a consanguineous family with AR-CMT. METHODS Two young sisters with AR-CMT and other non-affected family members were clinically and electrophysiologically evaluated and then molecular genetic investigation was carried out in order to identify the pathogenic mutation. RESULTS Following an initial indication for linkage of the family to the CMT4A locus on chromosome 8, we sequenced the Ganglioside-induced differentiation-associated protein 1 (GDAP1) gene and identified a single nucleotide deletion in exon 3 that is associated with AR-CMT in the family. CONCLUSIONS We identified a novel GDAP1 439delA mutation that is associated with AR-CMT in a consanguineous family of Iranian descent with two affected young girls and a history in other members of the family.

Genetic findings of Cypriot spinal muscular atrophy patients.

Spinal muscular atrophy (SMA) is an autosomal recessive, neurodegenerative disorder characterised commonly by proximal muscle weakness and wasting in the absence of sensory signs. Deletion or disruption of the SMN1 gene causes the disease. The SMN1 gene is located within an inverted duplication on chromosome 5q13 with the genes SMN2, NAIP and GTF2H2. MLPA analysis of 13 Cypriot SMA patients revealed that, 12 patients carried a homozygous SMN1 gene deletion and one patient carried two copies of the SMN1 gene. Two of 13 cases were a consequence of a paternally originating de novo mutation. Five genotypes were identified within the population, with the most frequent being a homozygous SMN1 and NAIP genes deletion. In conclusion, genotype–phenotype correlation revealed that SMN2 is inversely related to disease severity and that NAIP and GTF2H2 act as negative modifiers. This study provided, for the first time, a comprehensive overview of gene copy numbers and inheritance patterns within Cypriot SMA families.

Deregulation of LRSAM1 expression impairs the levels of TSG101, UBE2N, VPS28, MDM2 and EGFR

CMT is the most common hereditary neuromuscular disorder of the peripheral nervous system with a prevalence of 1/2500 individuals and it is caused by mutations in more than 80 genes. LRSAM1, a RING finger ubiquitin ligase also known as TSG101-associated ligase (TAL), has been associated with Charcot-Marie-Tooth disease type 2P (CMT2P) and to date eight causative mutations have been identified. Little is currently known on the pathogenetic mechanisms that lead to the disease. We investigated the effect of LRSAM1 deregulation on possible LRSAM1 interacting molecules in cell based models. Possible LRSAM1 interacting molecules were identified using protein-protein interaction databases and literature data. Expression analysis of these molecules was performed in both CMT2P patient and control lymphoblastoid cell lines as well as in LRSAM1 and TSG101 downregulated SH-SY5Y cells.TSG101, UBE2N, VPS28, EGFR and MDM2 levels were significantly decreased in the CMT2P patient lymphoblastoid cell line as well as in LRSAM1 downregulated cells. TSG101 downregulation had a significant effect only on the expression of VPS28 and MDM2 and it did not affect the levels of LRSAM1. This study confirms that LRSAM1 is a regulator of TSG101 expression. Furthermore, deregulation of LRSAM1 significantly affects the levels of UBE2N, VPS28, EGFR and MDM2.