Dominant-negative effects of a novel mutation in the filamin myopathy.

BACKGROUND: Filamin myopathy is associated with mutations in the filamin C gene (FLNC) and is a myofibrillar myopathy characterized by focal myofibrillar destruction and cytoplasmic aggregates containing several Z-disk-related proteins. METHODS: This study investigated 6 Japanese patients with dominantly inherited myofibrillar myopathy manifested by adult-onset, slow and progressive muscle weakness and atrophy in the distal extremities. RESULTS: The abundantly expressed proteins in the affected muscles were identified as filamin C by nano liquid chromatography-tandem mass spectrometry. A genetic analysis of FLNC identified a heterozygous c.8107delG mutation that was localized to the dimerization domain of filamin C. A biochemical crosslinking analysis of bacterially expressed recombinant wild-type and mutant filamin C fragments demonstrated that the mutant monomer disturbed the proper dimerization of the wild-type filamin dimer, resulting in formation of a heterotrimer with the wild-type filamin dimer. The expression study in C2C12 myoblasts showed that the mutant filamin fragments formed cytoplasmic aggregates with endogenous wild-type filamin C. CONCLUSIONS: This study provides evidence for the dominant-negative effects of the FLNC mutation. These effects may be mutation-specific and likely result in the variation in the clinical phenotypes seen in patients with filamin myopathy.