Muscular weakness is generally mild and
nonprogressive, but cardiac involvement has been described in some patients.
The cardiomyopathy can be congestive, hypertrophic, or restrictive,
sometimes requiring cardiac transplantation. Muscle weakness that begins in
infancy (“floppy baby”) is usually proximal, with hypotonia and decreased
muscle bulk. Ptosis and oculomotor palsy are sometimes observed. Motor
development is delayed, but intelligence is normal. Diaphragmatic
involvement can lead to hypoventilation during sleep.