The primary purpose of this study is to:

• Document the developmental outcomes of individuals with Pompe disease treated with long-term enzyme-replacement therapy (ERT) through school-age (ages 6-18) using measures of cognitive functioning, academic skills, and speech and language abilities.
• Investigate possible cognitive processing speed weaknesses using BrainBaseline neurocognitive assessment software.
• Investigate the relationship between behavior and other developmental factors including speech and language ability and cognitive ability.
• Explore if the use of selected iPad applications may help strengthen cognitive processing speed in children with Pompe disease

The study will last approximately 2-3 years. It includes 2-4 visits to Duke for developmental assessments. The baseline/year 1 visit may take place at Duke (may take 1-2 days) or remotely via iPad. The follow up 1/year 2 visit may take place at Duke (1-2 days) or remotely via an iPad, depending upon each child's particular situation.

Inclusion Criteria:

• Age range 6-18 years
• Diagnosis of classic Pompe disease by enzyme or molecular methods
• Patient, parent, or legal guardian is willing and able to give written informed consent
• English speaking child and care giver.

Exclusion Criteria:

This study is open to patients with classic Pompe disease.