- A severe form of the disease as defined as follows: a. Moderate to severe limb girdle muscle weakness requiring help for walking around (sticks, crutches, walking frame or wheelchair); and b. Symptoms of diaphragmatic dysfunction defined by at least 2 out of the 3 following criteria: orthopnea, vital capacity < 50%, paradoxical respiration detected in measurement of transdiaphragmatic pressure; and c. Use of invasive ventilation (defined by need for tracheotomy) or noninvasive ventilation (defined by utilization of assisted ventilation using a nasal or facial mask)day and night prescribed ≥ 12 hours/day;