Orofacial features include involvement of the masticatory, facial, ocular laryngeal, and pharyngeal muscles in late stages of disease. Motor nuclei of the medulla and often the pons and midbrain are involved. Lung hypoventilation, pneumonia, bronchopneumonia, and respiratory failure. The syndrome is transmitted as an X-linked trait but some cases are sporadic. Both Becker and Duchenne types are mapped to Xp21.3-p21.1.
Most mutations are deletions of one or several exons in the dystrophin gene.