How much mutant protein is needed to cause a protein aggregate myopathy in vivo? Lessons from an exceptional desminopathy

Hum Mutat. 2009 Mar;30(3):E490-9. doi: 10.1002/humu.20941.


Myofibrillar myopathies are caused by mutations in desmin, alphaB-crystallin, myotilin, ZASP, and filamin C genes. Since the vast majority of myofibrillar myopathy causing mutations are heterozygous single amino acid substitutions or small in-frame deletions, the pathogenic role of mutant versus wild-type protein cannot be assessed in human skeletal muscle by standard immunodetection techniques. We report on an exceptional desminopathy due to a heterozygous c.735G>C mutation. Immunoblotting detected full-length 53 kDa desmin and a truncated 50 kDa variant in skeletal muscle from three affected patients of two different families. RT-PCR identified three desmin mRNA species encoding for wild-type and two mutant proteins, p.Glu245Asp and p.Asp214_Glu245del. Since previous functional studies on the p.Glu245Asp mutant showed biological properties identical to wild-type desmin, the truncated p.Asp214_Glu245del desmin is the disease-causing mutant. Semiquantitative RT-PCR established a fraction of the truncated desmin mRNA species in a range from 24% to 37%. Initial quantification of corresponding desmin proteins in the muscle biopsy of the index patient of one family indicated a fraction of only 10% of the truncated species. However, serial analyses of different sections from each muscle biopsy revealed a high intra- and interindividual variability of the truncated desmin protein level within a range from 5% to 43%. Desmin assembly studies in vitro have established clear-cut pathogenic ratios of mutant versus wild-type proteins. However, our findings point out a far more complex situation in human skeletal muscle. The heterogeneously distributed mutation load within and between individual specimens, which reflects local differences in the expression and/or turnover of the mutant protein in different areas containing multiple myonuclear domains, renders it impossible to define an exact pathogenic threshold of a specific mutant in vivo.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Blotting, Western
  • DNA Mutational Analysis
  • Desmin / chemistry
  • Desmin / genetics*
  • Desmin / metabolism
  • Family Health
  • Female
  • Gene Expression
  • Humans
  • Male
  • Microscopy, Electron
  • Muscle, Skeletal / metabolism
  • Muscle, Skeletal / pathology
  • Muscle, Skeletal / ultrastructure
  • Muscular Diseases / genetics*
  • Muscular Diseases / metabolism
  • Muscular Diseases / pathology
  • Mutation*
  • Pedigree
  • Reverse Transcriptase Polymerase Chain Reaction
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization


  • Desmin