characterization of the in vitro expressed autoimmune rippling muscle disease immunogenic domain of human titin encoded by ttn exons 248249 autoimmune rippling muscle disease armd is an autoimmune neuromuscular disease associated with myasthenia gravis mg past studies in our laboratory recognized a very high molecular weight skeletal muscle protein antigen identified by armd patient antisera as the titin isoform these past studies used antisera from armd and mg patients as probes to screen a human skeletal muscle cdna library and several pbluescript clones revealed supporting expression of immunoreactive peptides this study characterizes the products of subcloning the titin immunoreactive domain into pgex3x and the subsequent fusion protein sequence analysis of the fusion gene indicates the cloned titin domain genbank id eu428784 is in frame and is derived from a sequence of n2a spanning the exons 248250 an area that encodes the fibronectin iii domain pcr and ecor1 restriction mapping studies have demonstrated that the inserted cdna is of a size that is predicted by bioinformatics analysis of the subclone expression of the fusion protein result in the isolation of a polypeptide of 52 kda consistent with the predicted inferred amino acid sequence immunoblot experiments of the fusion protein using rippling musclemyasthenia gravis antisera demonstrate that only the titin domain is immunoreactive