Types based on age of onset:
(1) severe neonatal
(2) mild congenital ("classic")
(3) childhood onset
(4) adult onset
Features of severe neonatal disease:
(1) presents at birth with severe muscle weakness and hypotonia
(2) respiratory insufficiency
(3) difficulty sucking and swallowing
(4) aspiration pneumonia
(5) rarely cardiomyopathy or arthrogryposis
(6) death common in early infancy
Features of mild to moderate congenital disease:
(1) onset at birth or during infancy
(2) hypotonia and weakness not as severe as that seen in the severe neonatal form
(3) feeding difficulty
(4) abnormal speech
(5) waddling gait and foot drop
(6) proximal and distal muscle weakness
(7) impaired respirations
(8) myopathic facies
(9) weak or absent deep tendon reflexes
(10) joint hypermobility
Features of childhood onset type:
(1) onset during childhood or adolescence
(2) may present with an abnormal gait associated with ankle weakness
(3) progressive proximal muscle weakness
(4) intestinal pseudo-obstruction
Features of adult onset type:
(1) may present with a cardiomyopathy
(2) impaired respiration
(3) slowly progressive proximal muscle weakness with or without distal muscle weakness
