Myofibrillar myopathies (MFM, OMIM 601419), muscular diseases characterized by the presence of protein aggregates, have been defined at the histopathological level by a sarcoplasmic accumulation of granulofilamentous material, desmin-positive protein aggregates, and degenerative changes in the myofibrillar apparatus (reviewed in [7–10]). The gene discussed is DES; the disease is myofibrillar myopathy.