A muscular dystrophy that is characterized by diminished muscle tone (hypotonia), progressive muscle weakness and degeneration (atrophy), abnormally fixed joints, spinal rigidity, and delays in reaching motor milestones such as sitting or standing unassisted. [ http://purl.obolibrary.org/obo/ECO_0007636 http://purl.obolibrary.org/obo/ECO_0007637 ]