Premium
How much mutant protein is needed to cause a protein aggregate myopathy in vivo? Lessons from an exceptional desminopathy
Author(s) -
Clemen Christoph S.,
Fischer Dirk,
Reimann Jens,
Eichinger Ludwig,
Müller Clemens R.,
Müller Harald D.,
Goebel Hans H.,
Schröder Rolf
Publication year - 2009
Publication title -
human mutation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 162
eISSN - 1098-1004
pISSN - 1059-7794
DOI - 10.1002/humu.20941
Subject(s) - desmin , biology , mutant , microbiology and biotechnology , skeletal muscle , myofibril , myopathy , filamin , wild type , mutant protein , point mutation , mutation , genetics , gene , biochemistry , anatomy , cytoskeleton , immunology , vimentin , immunohistochemistry , cell
Myofibrillar myopathies are caused by mutations in desmin, B‐crystallin, myotilin, ZASP, and filamin 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 53desmin and a truncated 50variant 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. © 2008 Wiley‐Liss, Inc.