The QMFT is an observer administered test to evaluate changes in motor function. QMFT comprises of 16 items specifically difficult for participants with Pompe disease. Each item is scored separately on a 5-point ordinal scale (ranged from 0 to 4, higher score indicated better outcome). Total QMFT score is obtained by adding the scores of all items and ranged from 0 (unable to perform motor function tests) to 64 (normal muscle function), higher score represented better outcome.

FVC is a standard pulmonary function test used to quantify respiratory muscle weakness. FVC is the volume of air (in liters) that can be forcibly blown out after full inspiration in the upright position, also tested in supine position. Percent of predicted FVC = (actual FVC measurement)/(predicted value of FVC) * 100.

Maximum Inspiratory Pressure (MIP) is a quick and non-invasive test to measure strength of inspiratory muscles, primarily diaphragm, and allows for assessment of ventilatory failure, restrictive lung disease and respiratory muscle strength. MIP refers to how much air pressure force an individual creates by inhaling through the mouth as hard as possible.

Maximum Expiratory Pressure (MEP) is a quick and non-invasive test to measure strength of expiratory muscles, primarily diaphragm, and allows for assessment of ventilatory failure, restrictive lung disease and respiratory muscle strength. MEP is the greater pressure generated during maximal expiration.

SF-12, a 12 item-questionnaire, used to assess health-related quality of life in participants aged >=18 years at screening/baseline. SF-12 consisted of 12 items, which were categorized into eight domains (subscales) of functioning and well-being: physical functioning, role-physical, role emotional, mental health, bodily pain, general health, vitality and social functioning, with each domain score ranged from 0 (poor health) to 100 (better health), higher scores indicated good health condition. These eight domains were further summarized into 2 summary scores, physical component summary (PCS) and mental component summary (MCS). The score range for each of these 2 summary scores was from 0 (poor health) to 100 (better health), higher scores indicated a better health-related quality of life.

The 24-hour recall PDSS (V1.1) is a self-administered questionnaires specifically designed to capture the symptoms impacts relevant to patients with LOPD. The PDSS includes 12 questions with responses on a scale from 0 (none) to 10 (as bad as I can imagine) The data from PDSS scale will be analyzed separately and as a composite with PDIS scale.

The 24-hour recall PDIS (V1.2) is a self-administered questionnaires specifically designed to capture disease impacts relevant to patients with LOPD. The PDIS includes 15 questions with varying scales implemented depending on question type. The data from PDIS scale will be analyzed separately and as a composite with PDSS scale.

The Pompe-PEDI consists of a Functional Skills Scale and a Caregiver Assistance Scale. Both scales have 3 domains: self-care; mobility; and social function. The Mobility Domain was selected to measure change in mobility secondary to changes in muscle strength. The domain consists of 160 mobility items.

The 23item PedsQL Generic Core Scale encompasses 4 subscales including physical, emotional, school, and social functionings. Scores are transformed to a 0-100 scale, higher scores indicate better HRQOL.

Infant scale will not be used since this is a scale for up to 24 months of age and patients are older now than that.

Left Ventricular Mass Index (LVMI) equivalent to mean age specific LVMI plus 2 standard deviations.