Pompe disease has two forms, so it is important to check which one you are learning or reading about.
The two forms are infantile-onset Pompe disease and late-onset Pompe disease.
In the case of infantile-onset Pompe disease, patients do not express any GAA enzyme at all and develop symptoms very early in life, during the first months after birth. Symptoms consist of generalized muscle weakness, floppiness, swallowing difficulties, and respiratory and cardiac insufficiency. Cardiac problems are the most severe symptoms in these cases; if the patients are not treated, they could lead to death. Fortunately, enzymatic replacement, which is the standard for care treatment of this disease reverts cardiac problems extending the life of patients and leading to a variable degree of improvement in skeletal muscle weakness.
Late-onset Pompe disease patients present very heterogeneously, ranging from just isolated hyperCKemia (an increase in creatin-kinase levels in blood not associated with any symptom) to limb-girdle progressive muscle weakness. Most of the patients develop muscle weakness during their life that is variable in severity and tend to associate with respiratory involvement. Treatment with ERT has a positive impact on the disease, mainly slowing down disease progression, although muscle weakness could continue to progress despite the treatment.