Defects in MYH2 are the cause of inclusion body myopathy type 3 (IBM3) [MIM:605637]. Hereditary inclusion body myopathies constitute a group of neuromuscular disorders characterized by slowly progressive distal and proximal weakness and a typical muscle pathology including rimmed vacuoles and filamentous inclusions. IBM3 is a variant of hereditary inclusion body myopathies and is characterized by autosomal dominant myopathy with joint contracture, ophthalmoplegia and rimmed vacuoles. Morphological analysis of muscle biopsies from patients indicate that the type 2A fibers frequently were abnormal, whereas other fiber types appeared normal.