Safety and Efficacy of Avalglucosidase Alfa in Patients With Non-classic Pompe Disease Aged ≥ 5 Years

Rationale: Not all patients with non-classic Pompe disease have a good response to current treatment with alglucosidase alfa. Therefore innovative enzyme replacement therapies are developed. The study drug avalglucosidase alfa has been tested in multiple clinical studies and will now be studied in a small population of patients that are unresponsive to alglucosidase alfa. Objective: To explore safety, tolerability and efficacy of avalglucosidase alfa in patients with non-classic Pompe disease aged ≥ 5 years of whom clinical condition deteriorates while on standard treatment with alglucosidase alfa. Study design: Single-center, open-label, repeated bi-weekly intravenous infusion study of avalglucosidase alfa in patients with non-classic Pompe disease patients aged ≥ 5 years, previously treated with alglucosidase alfa. Study population: Non-classic Pompe disease patients aged ≥ 5 years and ≤ 55 years previously treated ≥ 2 years with alglucosidase alfa, who deteriorate despite treatment with alglucosidase alfa at a dose of 20 or 40 mg/kg bi-weekly. Total number of patients = 6. Intervention: Avalglucosidase alfa. Sterile lyophilized powder administered by intravenous infusion following reconstitution and dilution. 20 mg/kg bi-weekly Main study parameters: * Safety * Assessment of adverse events / treatment-emergent adverse events, including infusion associated reactions (IARs) * Clinical laboratory evaluations including hematology, biochemistry, urinalysis * Immunogenicity assessments * Pharmacokinetics • Single and multiple dose estimates for Cmax, AUC, CL,. * Efficacy * Muscle strength: manual muscle testing (MMT), hand- held dynamometry (HHD). * Muscle function: Quick Motor Function test (QMFT), six Minute Walk Test (6MWT), timed tests. * Pulmonary function: (forced) vital capacity ((F)VC) in sitting and supine positions, Maximum Inspiratory Pressure (MIP), Maximum Expiratory Pressure (MEP). * 'PRO-measures': Rasch-build Pompe Activity scale (R- Pact), Quality of Life (QoL), modified Borg scale, Nature and extent of burden and risks associated with participation, benefit and group relatedness: Blood samples will be collected at 14 time points, the amount of blood will not exceed the maximum amount of 5 ML/kg over a period of 8 weeks. Patients will visit the hospital every other week to receive treatment. This treatment will last 4-6 hours. During every visit the vital signs of the patients will be checked and a physical examination is performed.