Nebulin is a giant protein component of the cytoskeletal matrix that coexists with the thick and thin filaments within the sarcomeres of skeletal muscle. In most vertebrates, nebulin accounts for 3 to 4% of the total myofibrillar protein and its size varies from 600 to 800 kD in a manner that is tissue-, species-, and developmental stage-specific. The nebulin gene contains 183 exons in a 249-kb genomic region. Nebulin is mapped to chromosome 2. Nebulin is a giant filamentous protein specific for vertebrate skeletal muscles. Mutations in the nebulin gene associated with autosomal recessive nemaline myopathy.