emerin and Muscular-Diseases

Exon skipping, as a therapy to restore a reading frame or switch protein isoforms, is under clinical trial. We hypothesised that removing an in-frame exon containing a mutation could also improve pathogenic phenotypes. Our model is laminopathies: incurable tissue-specific degenerative diseases associated with LMNA mutations. LMNA encodes A-type lamins, that together with B-type lamins, form the nuclear lamina. Lamins contain an alpha-helical central rod domain composed of multiple heptad repeats. Eliminating LMNA exon 3 or 5 removes six heptad repeats, so shortens, but should not otherwise significantly alter, the alpha-helix. Human Lamin A or Lamin C with a deletion corresponding to amino acids encoded by exon 5 (Lamin A/C-Δ5) localised normally in murine lmna-null cells, rescuing both nuclear shape and endogenous Lamin B1/emerin distribution. However, Lamin A carrying pathogenic mutations in exon 3 or 5, or Lamin A/C-Δ3, did not. Furthermore, Lamin A/C-Δ5 was not deleterious to wild-type cells, unlike the other Lamin A mutants including Lamin A/C-Δ3. Thus Lamin A/C-Δ5 function as effectively as wild-type Lamin A/C and better than mutant versions. Antisense oligonucleotides skipped LMNA exon 5 in human cells, demonstrating the possibility of treating certain laminopathies with this approach. This proof-of-concept is the first to report the therapeutic potential of exon skipping for diseases arising from missense mutations.

Topics: Animals; Exons; Genetic Therapy; Genetic Vectors; Lamins; Membrane Proteins; Mice, Inbred C57BL; Muscular Diseases; Mutation, Missense; Nuclear Proteins

To clarify the occurrence of apoptosis in skeletal muscle in pathological conditions, we studied 44 muscle biopsy specimens by immunohistochemical staining with monoclonal antibody against emerin, which is localized in muscle nuclear membrane, and by ApopTag Plus to detect DNA fragmentation. Five of six patients with myotonic dystrophy (DM) showed three to 35 myonuclei stained with anti-emerin antibody and ApopTag Plus in 1500 muscle fibers. Four of the 18 patients with polymyositis, one of those with thyroid myopathy and one with neurogenic atrophy showed a few myonuclei stained positively by these methods. Our study revealed that DNA fragmentation in myonuclei occurred in skeletal muscle fibers regardless of the type of disease, although the frequency was rather low in all of these diseases except DM. The DNA fragmentation detected in most of the patients with DM suggested a significant role of apoptosis in the pathomechanism of this disease.

Topics: Adolescent; Adult; Antibodies, Monoclonal; Apoptosis; Biomarkers; Cell Nucleus; DNA Fragmentation; Female; Humans; In Situ Nick-End Labeling; Male; Membrane Proteins; Middle Aged; Muscle Proteins; Muscle, Skeletal; Muscular Diseases; Myotonic Dystrophy; Nuclear Proteins; Polymyositis; Thymopoietins

X-linked myopathy with excessive autophagy (XMEA, MIM 310440) is a rare inherited mild myopathy. We have used 32 polymorphic markers spanning the entire X chromosome to exclude most of the chromosome except the Xq28 region in a large XMEA family. Using three additional families for linkage analysis, we have obtained a significant two-point lod score with marker DXS1183 (Z = 2.69 at theta = 0). Multipoint linkage analysis confirmed the assignment of the disease locus with a maximal lod score of 2.74 obtained at recombination fraction zero. Linkage of XMEA to the Xq28 region is thus firmly established. In addition, we have ruled out the Emery-Dreifuss muscular dystrophy to be allelic with XMEA by direct sequencing of the emerin gene in three of our families.

Topics: Biopsy; Chromosome Mapping; DNA; Family Health; Female; Genetic Linkage; Haplotypes; Humans; Lod Score; Male; Membrane Proteins; Microsatellite Repeats; Muscle, Skeletal; Muscular Diseases; Mutation; Nuclear Proteins; Pedigree; Sequence Analysis, DNA; Thymopoietins; X Chromosome