Atrophy of fast myofibers is a common feature in several myopathies but is poorly recapitulated in animal models. Mutations in the gene encoding leiomodin-3 (LMOD3) have been detected in individuals with nemaline myopathy (NM), a common congenital disorder associated with muscle weakness and the presence of rod-like structures (nemaline bodies) in both fast and slow skeletal muscle fibers. To shed light on LMOD3 function in NM, Tian Xu and collaborators generated a mouse mutant in which they disrupted the expression of the LMOD3 gene. These mutants show typical features of NM, including severe muscle weakness, postnatal growth retardation, and nemaline bodies and disorganized sarcomeric structures in the skeletal muscles. Notably, these animals exhibit atrophy specifically in fast myofibers. LMOD3 mutant mice are the first to experimentally model fast-myofiber atrophy, a unique clinical feature of several human myopathies. This mouse mutant can thus be used to further elucidate disease mechanisms and to identify potential targets for therapeutic purposes. Page 635

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