In the neonatal period, hypotonia and muscle
weakness produce swallowing problems and weak cry; severe cases progressing
rapidly to respiratory failure are described. Motor development (walking) is
delayed. Muscle mass is thin; truncal and proximal muscles are most
affected, but distal limb, pharyngeal, and facial muscles can be involved.
The face is usually long with a high-arched palate, malocclusion,
prognathism, or micrognathia. Abnormal gait. Normal intelligence. Scoliosis
and intercostal muscle weakness produce severe restrictive lung disease.
Congenital heart disease or cardiomyopathy may be rarely present.