Interestingly,severe respiratory insufficiency can occur in Pompe disease with-out evidence for significant limb muscle weakness. For example,there is only a weak relationship between indices of respira-tory and locomotor function in adults with Pompe disease, andsevere respiratory insufficiency can be present without any evi-dence of limb girdle muscle weakness (Pellegrini et al., 2005). Thephysiological reasons for this observation are not clear, but couldrelate to increases in the metabolic activity of respiratory mus-cles and neurons as compared to other skeletal motor systems.In any case, it appears that the respiratory neuromuscular sys-tem is particularly susceptible to dysfunction in Pompe diseasewhich is a unique aspect compared to other forms of musculardystrophy in which loss of ambulation precedes ventilatory insuf-ficiency.