Congenital myotonic form is more severe. Progression is slow, sometimes spanning 50 to 60 years. First affects muscles of eyelid and throat. Slow progression with swallowing problems common as disease progresses. Slow progression but not life-threatening.
Fukuyama form is more severe and involves mental functions.
Usually progresses rapidly with 3 to 5 year average survival. Autosomal dominant, autosomal recessive. Cannot sit up. Progresses very rapidly with early childhood death. Weakness in arms, legs, upper and lower torso, often with skeletal deformities.