Early-onset (or Classic infantile Pompe disease) is the result of complete or near-complete deficiency of the enzyme alpha-glucosidase.
Symptoms begin in the first months of life, with feeding problems, poor weight gain, muscle weakness, floppiness, and head lag.
Respiratory difficulties are often complicated by lung infections. The heart is grossly enlarged. More than half of all infants with Pompe disease also have enlarged tongues.
Without treatment within a few days of birth, most babies with Pompe disease die from cardiac or respiratory complications before their first birthday.